Ben1098

Check the spark plug. Tells the fuel air mixture ratio. Tan color is what you want. A fouled plug....dark and or sooty will blow out (not spark) under heavy ignition energy requirement such as acceleration. Example was late night bed roll traveling H-D Sporty rider who wanted to "impress" me (sitting on a V65 Honda---V4 of grunt) while waiting on him so I could pull out after he went by. Yellow headlight......his regulator has croaked.....battery getting low on minimum ignition voltage level. Predictable cough stumble, and misfire instead of hearing his shorty pipes go by. Tailed him waiting for the death knoll. 6 miles later on a gradual uphill 3/8 mile long hill......he puked.....Naturally, I slowed for him to pull over and land so he could see with my headlight.......then give him a 1st gear 60MPH redline header romp. Now, that is what is what it should sound like. Gone. Lots of info in the above short story. Weak ignition will run ad idle but fail under load. Fouled spark plug. Ignition wiring rubbing on sharp metal edge and a partial insulation failure.....will only corona (ring of fire) under load. Fuel air mix.....BOTH a right mixture and lean mixture will foul a plug. Rich is obvious. Lean mix gives a misfire and UNBURNED fuel to wet down the plug and then fail. Mice.....remove air intake plumbing to give free air at the carb inlet. Check air box and all plumbing for mouse house. Fuel pump diaphragm getting hard....low fuel level in the carb bowl. Test bottle of gas for this test. Last...............bad pump gas...getting bad here over non-national gas station buyouts. My favorite station (always good gas for old Ford gas tractor and Grasshopper). Station bought out.....didn't know. Bought 8 cans of junk premium 93 and when used, the Grasshopper run OK for about a minute. Switched on the deck and died....hard to restart....pulled back to shed and drained slop.

I did a still frame of the little blue flash around 35/38 sec.......that is a problem......to get this, you have 2 problems going on. 1. Intake valve leaking or open-----bent (timing wrong and dinged the piston) or no valve clearance. Leak down test and listen for air whistle. 2. Intake leak in the casting area after the carb intake air boot. The lean air mixture "spit" will also cause the faster idle speed. Recheck the ign timing with the copper wire "feeler depth gauge" TDC piston location. Check that the cam lobes are pointed down-----valves closed and not on overlap and then paint dot the cam index point at 12 o'clock......the dimple is under the metal tab covering the flyweights. I posted a detailed instructions in an earlier post about the paint the cam trick. Recheck the valve clearance. Ensure you are not on the decompression pin for the exhaust valve adjustment.......rotate the flyweights to retract the decompression pin. The BLUE FLASH. Visual. By the size of the blue flash it has to be easy to spot.

Massimo badged HiSun clones has the diodehiding deep inside the wiring harness. Pass side of the machine, radiator side of the firewall. Look for a thick harness bundle run toward the pass side then turns downward.......the diode is DEEP inside the lump of cable going down.....were the wire color changes from the brn-??? IGN ON (HOT) to the black-red tracer going to the switch. AIN"T WORTH IT. Jump from the IGN ON HOT to the blk-red wire.....If you DO want the snuffer diode, insert at the new joint but have the diode band on the blk-red wire

If the new boot is a good fit and function, buy...... Cheaper than engine rebuild if you use on dusty trails. The boot might be petrified anyways. Down side is there might have been different jetting and/or a different spring constant----the stiffness of compressing the spring. The diaphragm slide spring selection is a calibration of spring stiffness, length, and the needle hanging out of the bottom of the slide. The slide position (air flow and fuel from the main jet) = engine RPM.... is determined by the difference in air pressures vs the spring pushing it back closed. These stupid "I need the more speed" wantabe racers have problems with the carb hop up kits like race and full race for crotch rockets-----which literally fouls the plugs when just idle cruising the WHIP. If the air boot modification changes the runability, simply disconnect and and plug---most noticeable when the air filter is starting to get clogged----restricted......changes the designed pressure difference at the slide porting. Try and see.

OFF....both the small tube and the bigger atom vent tube stay open. The tube out of the bottom of the carb fuel bowl is smaller in diameter. That is the gasoline overflow drain for the bowl. Look at the bowl's other side bottom and you might find a screw head, OR a boss pad that COULD be drilled-tapped for the screw. EPA restrictions and/or bean counters deleted the function. This screw (with a tapered end) lets gas will drain from the bowl when cracked open. The bowl drain hose should be open. The external nipple the hose is connected to goes inside the carb to an open ended vertical brass tube. Think of a standing drain pipe for a lake overflow. Function is to keep a flooding carb from filling to the point where raw gasoline runs into the engine cylinder----wash down. The atom vent hose bottom is an open drain. TRICK--------squirt some oil into the hose bottom but now fill to the "T". Blow excess for just a coating that keeps bugs from becoming a squatter. Q. for you. Picture is framed too low. You routed the atm vent thru the air boot molded mounting.......DID YOU FIND A SPOT to connect to WHERE THERE IS FILTERED AIR?

Open drain for dust and water to get in. High water will get sucked in by manifold vacuum if a bug calls the other end home. The vent inside the carb goes directly to the bowl. Water sits on the bottom, jets cannot flow with higher viscosity water and DEAD.

The T hose would be the CV carb's atmospheric vent. The problem with the open ended hose is bugs and dust. Bugs build nests and block off the vent. Dust ingestion is bad for the engine. Older motorcycles would have the open end routed to the INSIDE of the air box and it's own little filter. Yamaha 750/920 Virago vents went to a pair frame mounted steel tubes......open ended.......wasps loved these open ended tubes under the steering head.. Test hose assy by removing the tube at the carb (between the CV slide and the intake horn). Blow shop air thru the just removed tube and it should flow out both the ends. Install a clean tube to the carb and mouth blow air into the tube. You should have no resistance down to the carb bowl and and if blown hard enough, you can bubble gasoline up thru the fuel jets. Function......the fuel bowl has fuel sucked up thru the pilot jet (idle), main jet, and the fuel enrichment (choke cable on the left in the picture. For the fuel to flow, a pressure difference is required.......intake creates a vacuum relative to the bowl's ambient air pressure. Also, the CV carb needs the pressure difference to open the slide against the spring. For funnys, put your finger over the hose nipple and see how the engine stumbles. Now, I see on the air intake rubber tube it has a molded push in tube mount....very close to the end of the tube in your photo. Check around the air box......there might be a hose connector to connect to.

Compression release not lowering the fuel-air mix pressure. Start T/S with removing the spark plug. Put back on the boot and ground the threads away from the open plug hole. Crank over......if it cranks without stalling, the compression release is the culprit. Next, you need to remove both the valve adj lids and the round side of head cover for the cam gear. Rotate the crank and bring the piston to TDC....use a bare copper wire thru the plug hole to feel the TDC highest position of the piston dome. NOTE: there are 2 TWO TDC positions on a 4 stroke engine. OVERLAP.....Exhaust valve just closing and the Intake vale just opening. This not the one you want to mark the cam gear. Rotate the crank a full 360 deg and recheck the valves.......Both should be closed with the cam lobes facing away from the rocker slipper pads. White paint the top 12 o'clock position tooth. Next, check the intake and exhaust valves rockers for the spec clearance. Now for the good part.....the compression release cam within the cam center bore. I did a post a couple months back: T/S a no start with spark that ended up being the wrong Delphi ECM module....timing off by 90 deg. Find this series of posts and it explains the compression release mini cam......the small dime sized disk with the flyweights "pin coupled" at the very center of the cam gear face outside. In a nut shell, rotate the mini cam disk.... Sling weights moved out against the springs tension. The mini cam pushes up an internal pin against the exhaust rocker thus holding the exhaust valve for a short time to bleed off some compression and then the starter can spin over the motor. Things that go wrong: 1. Valve adjustment wrong. Rotate the crank/cam slightly off the pin or hand rotate the weights out to lower the pin and now be able to adjust the valve clearance. Now to check the operation of the decompression release pin rubbing the exhaust rocker. Rotate the crank backwards a couple of teeth on the cam gear. Rotate forward and watch the exhaust rocker. The rocker should hold the exhaust valve slightly open and then snap closed as the pin rotates past the rocker slipper pad. Repeat the reverse rotation and this time rotate the flyweights out to unload the pin.....the rocker should not snap back and have the spec clearance. 2. If the pin did not do anything....as in no compression release......you might have the "pin grove" gouged out of the slipper pad. The rocker shaft needs to be removed with a slide hammer. Check the rocker compression slipper pad....small tab vs. the much wider cam lobe slipper pad for inspection. The gouged out stripe will be obvious.

COMMENT that Reverse works fine..........no bog down as in it revs up ok? See rev limiter posts to bypass at the ECM.......MC DOCTOR has good drawings.

This SERIES snubber diode is to BLOCK the reverse EMF (voltage spike) created when the power is interupted by the thermo fan switch (current stops and the magnetic field of the DC motor collapses). In industrial applications with the control voltage circuits using 24 VDC, the relays will have a SHUNT snubber diode across the coil relay terminals (cathode on the + 24 v terminal and the anode to the - side..........that is put in backwards. The PLC's electronic driver switch, hates to have a back hit from the relay coils turn off (- spike components of the waveform) EMF spike. 120 VAC control voltage circuits relays do not require the diode (would fry on power up). A good visual example is to take an old style Ignition coil and feed 12 Vdc to the + post with and the - or gnd post tied to the - side. Coils were actually 6-8 V and the resistance wire in the harness (GM) or the Chrysler ballast block dropped the voltage to 6 V. Touch and remove the +12 v feed wire....notice the reverse voltage arc flash.....better yet, for a shocking example of what NOT TO DO is grab a good ground and touch the bare wire end of the feed when opening the circuit....the hole in your finger tip will grow back. The magnetic field from the current flow is stored energy........cut the current flow.....the energy has to go somewhere (other than to the high voltage side of the coil. That is why points burn up with a pit and a mound. The size of the capacitor (condenser) is "matched" to the ignition coils "L". The capacitor value size above or below the "ideal match" value will result in the deposit (triangle mound) to be on the base contact or the movable arm contact. The worst thing to do to an old points ignition motor.....TUNE UP. New points and condenser. If the points had little deposit transfer, the capacitor was a good match.......long point service life......only to be thrown away and a new RANDOM value capacitor installed THAT NIGHT NOT BE A GOOD MATCH. Time to quit.

Surprise answer. The units are Yamaha Rhino clones. Yamaha put in a SERIES DIODE SNUBBER........ready for this.......inside the wiring harness. The Massimo 500 units have this diode on the passenger side wiring harness trunk line about half way down the vertical run of the wrapped harness bundle (buried inside the bundle to boot).....along with a wire color change at the diode. Let's make it easy here!!!!!!!!! Not worth digging and cutting the wrap for the diode. Feed is the ignition switch ON lead. When the diode OPENS, the circuit end at the diode. I would tie a wire to the IGN switch ON lug, fuse with a inline 10 A, and then to the itty bitty red/blk wire. Do this jack leg fix and then jumper the fan thermo switch to test....and don't look back.

Quick test. Sounds like the fuel pump is not keeping up with demand. After the 30 sec or so run time, and starts to die, give it a wiff of starter fluid and see if it recovers........fuel starved. Key OFF wait 5 sec or so....Key ON only------no start position. The fuel pump is turned on for about 5 sec to PRIME/PRESSURIZE fuel rail.....signal is from the ECM.......wait it out for time out......then start. Listen for the short prime time running. Start.....ECM should now keep the fuel pump full time. Put a test light on the pump connector (clamp to Gnd) and check for 12v. Then reverse the clamp connector from Ground to a hot +12v.....you can now check for a good ground at the connector.

HS800.....should be HS500. See Motorcycle Doctor store....has several units for the HiSun 500. While you are talking, confirm the flywheel P/N also. Talk about going 20 steps backwards...............been there as we usually ended up with the dogs after $$$$$$$$$$$$$$$$ wasted and they did NOT usually get the "good" parts back as there are no returns on electrical. My personal best was a Honda 350 ATV. Dead IGNITION. 3 H shops, 1 Independent. Shotgun parts. Had thick folder. From Chicago area. Drove down and stood in line a busy (pulled up front) Sat AM. Seen ALL parts for the IGN replaced shop WO parts list. Clue: Asked what he used it for. IDNR food plots. OH! Took clip lead and meter to his PU. T/S in the bed......first guess at the sales counter was right. Run. Boss didn't even know I left. He was charged for 7 minutes. MY take on the whole story...............exhaust cam wear and low compression was the initial killer. CHOW.....hope you finally win. BEN

20 sec video. Hit play. Time bar slider moves. Any tap on the blank screen throws me into full screen. no audio, no video. Times out---done. UTube video. I see the white mark "flashing" at the 90 deg point (9 o'clock with 12 being the cast index in the head). Confirm the cam lobes are down (valves closed) when the white mark on cam gear is at the top (12 o'clock) position and piston is at the very top TDC. If you got that, you are timed mechanically. If that is correct, you have one of three things going on: 1. The flywheel buttons or tabs "missing or skip tab" is off relative to the flywheel center keyway....which is locked to the crankshaft. The TDC was confirmed with the Cu wire test touching the top of the piston. Inside, the 18 knuckle poles stator (3 Ph. gives 6 magnet pairs) are independent of tabs on the rim...charging only. 2. Wrong part # ECM (DElLPHI MT05).......The pin outs are all the same. Software maps and advance curves are what change per application.. OR 3. The MT05 is for a 90 deg V twin motor w/ dual coil outputs.......... example is the KAW and KOHLER engines used on high end Zero-Turn mowers. The MT05 has 2 coil output pins: COIL A is pin J1-10 w/ J1 is Grey and COIL B is Pin J2-01 w/ J2 is Black Prior techs swap the pins???? eBAY Store of MOTORCYCLE DOCTOR. He carries HiSun parts and P/N. You have 2 parts to check out. Seen he has helped others on this forum. BEN

Dimmed my monitor............I SEE......Your timing is out in the weeds like 90 deg at the cam=180 deg at the crank. Cam gear is upside down to the cam punch mark. Same as I saw in your still a couple posts back. Revisit the cam gear installation. Before taking the cam gear off, rotate the engine to the TDC (with painted cam gear at the casting mark) as before. The rockers should be up (valves closed). Look into the rocker valve adj lid hole at the rockers. The cam lobes (BOTH) should be down....no lift on the rocker and the valves closed. For this timing, you have to be in OVERLAP with the Exhaust going off and the Intake coming on at the second TDC of the 720 deg rotation per cycle. Ain't no 2 stroke. WARNING: This is sorta dangerous right now.......you got some spring energy wanting to eat your fingers if you remove the cam gear bolts. Rotate the crank until the cam lobes are down (COMPRESSION) and the valve springs are unloaded. Now safe to pull cam bolts. Check for the punch mark on the end of the cam.......should be pointing to the head casting timing mark. Match the cam gear, etc. BEN

Saw the UTube vids. Notice the "stall" and hard first crank turn over.............your compression release is NOT working.....starter is good and powering thru to get it spinning. I could not determine the flashes of the timing light from the video. Back to the Cu wire and finding the TDC mark. Degrease and put in a small white dot to mark (and be easier to quickly spot) just like the cam. Determine that this is still the case......no timing chain jump. Normally, RICE BURNER (old slang for the Japan Mfg, like LIMEY for British and CHINO is for HiSUN) machines cranks have 4 marks. TDC-----piston is at the top and rocks up and down as this timing mark is rocked back and forth with the crank. Cam gear dimple (now painted) will be at the cast notch at the top. F line......static timing line for low RPM (and cranking).......the ignition spark time......around 8 deg BTDC....have to manually turn backwards to this line from TDC. FULL ADVANCE spark line (dual parallel lines). The reason for the 2 lines close together......the high RPM advance is say 28 deg BTDC but there is some tolerance so the one mark might be 26 deg and the other 30 deg. Your cam gear has 46 teeth. Crank gear has 23 teeth........the 2:1 ratio required for the cam to run at 1/2 the crank RPM. Knowing this, you can do some quick math and determine each tooth at the cam is close to 7.8 deg each of the cam.....and close to 16 deg of the crank. The static (idle=8 deg) timing mark will have the cam gear rotate backwards about only 1/2 tooth at the cast head timing mark. The double parallel lines (FULL advance at 28 deg crank) would be close to the 2nd tooth back.................was used to check if the spark advanced as RPM increased to say 2200 RPM. You are describing the TDC single line and after you rotate backward the 0.50" the double lines.........STATIC (8 deg BTDC advance) timing mark.....about 1/2 tooth on the cam. Leave the spark plug out (pull the fuel pump connector) and repeat the timing light test-----will only have the plug hole whistle. WHAT LIGHTS UP and WHERE???? SHOULD have the cam's white dot move slightly BTDC....and of course the wasted spark. Do it in reduced light so the mark pops out on the video so I can see where the ECM is firing the IGNITION. BEN

WHOA THERE!!!!!!!!!!!!!!!!!!!!!!! Yes, I can do UTube vids. The pics of timing looks weird. You need another paint mark on the cam gear.......................the FIRE mark on the flywheel at the notch location transferred to the cam gear.. The flywheel in the first pics looks right with all the pick up coil buttons or tabs. You need to locate the "F" mark on the flywheel. Timing on most motors are in the 8-14 deg BTDC area.......the static timing mark at idle. As the engine RPM increases, the flame front cannot be at the same position away from the piston.....it takes time....very short time....for the flame front to reach the piston dome. The timing has to start sooner so the ADVANCE CURVE (caused by flyweights in the old points engines) or a Map in ECM units...........will slide from the idle of say 8 deg to something like 28 deg BTDC. Back to the flywheel. Hand turn the flywheel to the TDC mark used for cam timing. Now, slowly rotate the crank BACKWARDS. About 8 deg back, you should see a line with an F.....the idle fire timing mark. Mark the cam gear a second time at the head casting arrow. This will be the point where the timing light will flash at idle. Rotate backwards even more until you see 2 lines.......this if the full advance point of say 28 deg. This will slide into view when getting above say 2200 RPM. Not needed now. Repeat the timing light at the cam......your new or 2nd paint mark should be at the casting arrow.

HiSun may have changed the little mini cam rod profile shape so that the now NOT fully CCW disk rotation allows the pin to drop back into the shaft and not affect the decompression function. 5 years ago that was a bad batch of flyweights. Running Engr Changes are a problem out in the field. This engine has run before BUT it probably has had many hands in the soup. With these shop jumpers, sometimes you had to go back 20 steps just to get back to GROUND ZERO. How did a timing light check out? HINT: You can just shine the timing light on the cam and watch the paints at the cam.....BUT you will have a spark at the painted cam timing mark AND an "extra" flash when the cam is 180 out on the other gear mounting bolt. Anyways, your timing appears to be correct. You have good compression numbers. Lets drop back and check the spark plug. After cranking is the plug wet with fuel? These machines hate Chumpion plugs. Go with a new NGK....nothing fancy........ $$$$ tips not req'd. There were 2 versions of the injectors----the slobbering 2 hole and the spray 3 holer. Fuel pump pressure should be around 40 PSI. Exhaust restriction....like did mud dobbers make a summer home in the muffler? Mouse house in the air box and/or plumbing? Need good air flow in and out. Strip it back to just the basic engine. Pull the fuel pump connector.....removes possible fuel rich condition and ECM control of fuel management. Good known new dry spark plug.....use compressed air to dry the top of the piston and combustion chamber if flooded or wet down. Remove the air box to TB plumbing rubber tube.........just the throttle body and without any fuel. Manually turn the engine over until the exhaust valve is opened fully. Blow air into the spark plug hole like you are doing a leak down test. Does the air come out of the muffler with a clean unrestricted rush of air? Motor is just an air pump---has to have a good flow. Rotate engine until intake valve is open....same test cannot be done here as the MAP sensor doesn't like that. Open the throttle body (gas pedal) and direct the air at the spark plug hole....hear a good flow backwards out the TB? Combustion chamber has no residual fuel. Crank. Did it try to start? Shouldn't. Give the intake TB a short shot of starter fluid. You should at least get a try to fire and run.....dies after go juice used up......if the engine is solid, Start adding parts back to the system. Connect the air box rubber tube to the TB. TEST. Add back the air box with the lid removed. TEST Crank and supply the go juice as fuel to the air filter body. Give it longer bursts of go juice to see if engine will run for say 3-5 sec and die. Connect the fuel pump connector. KOn (key on) 2 -3 sec pump run to pressurize the fuel rail/tubing. Pull the fuel pump connector again. What this does is give the ECM a chance to fire it over BUT if a problem like too rich, it will not be "spoiled" again after the fuel rail pressure drops back....i.e. no more fuel. Should have a short fun and die. Short burst of go juice at air filter....same start and die? Looking for same results from before with longer bursts of go juice. Reconnect the fuel pump connector....KOn......TEST. Short burst of go juice. Fire up and continue to run or die? Need this info to go further. Try these things first............gets you to the big Y in the road..................you might not like the one path as it gets into Delphi MT05 ECM and it's inputs. Tell you what. The Delphi unit has GOOD online information and gives the I/O pinouts on a diagram. Look further back past the front section Engr Secs and look for the BLACK and GREY CONNECTOR drawings AND the full connection "wiring diagram" page....great if you also own a KAW lawn mower engine---uses the same basic module.

I assume the new latest pics are the new cam and head assy????? It has a problem. Poor mfg process information (instructions and drawings) never really go away. They always pop back up like the turd they are. I was flown to Mexico for multiple "mistakes" and to T/S with a "fix and rework"---clean up the build information----and only to find the same problem pop up again 6 months later from the sister supplier, This problem was on both Yamaha Rhino and Hisun cam assys a good 5 years ago. We had Massimo. Another shop had Yamaha. They chased a mystery problem to the cam assy. My new cam assy arrived (with the same runability problem) in the new uncrated unit.. I did the carbide burr air tool hand mill job on both sets. EXCESS WELDED WEIGHT GONE. Other shop has same problem. His flyweights had all the same machining, stamping marks...with welds identical.....the same sub supplier. My reworked flyweights were given away to fix the Rhino. Since you have the old cam, mark the flyweights to MATCH their wear "home" location. Remove and you should see the rub marks where the little disc hits the rear welded/attached weights. For the fun part: 1. Hold the whole cam assy and put the button head pin that sticks thru further to the inside by the exhaust cam lobe DOWN. Gravity is your friend. 2. Put your thumb on the button-----should push in below the cam "shaft" profile----as in not the lobes profile----Rotate the disk and the mini cam will push up the button. 3. Reverse and the button will retract again into the cam shaft area. See how the system works. 4. Pull out the small disk with the 2 flyweight engagement pins. 5. The "rod" attached (with the dogleg bend) is the minicam within the cam----used to push up the button pin that hits the extra tab on the exhaust side of the big valve cam. 6. With this pin out, the button can now fall into the hollow main cam center. Gravity----set down cam button down. If it falls to the center, no big loss. Just a pain to reinsert it into hits hole....ship in a bottle syndrome. 7. You should now see why the your adjustment is wrong. Rotation of the of the flyweights, rotates the small dime sized disk, which rotates the dogleg rod inside the hollow cam. 8. YUP, the end of the dog leg is what pushed the pin out further to engage the cam. BUT. if the small disk cannot fully rotate backwards, the button protrudes out too much and now does a compression release. 9. Your thinking now, why not just make the disc smaller in diameter........NOPE, not enough meat left for the pin hole wall thickness. BEN EXTRA correct operation Engine stopped. The springs pull the sling flyweights back. The mini cam (all you can see is the disk with the 2 pins) will push the button up and hold the exhaust valve slightly open.....only while the rocker's extra "tab"-----not the cam lobe------ is on the button.......after which time the regular exhaust cam lobe will them rub it's normal slipper pad. The is the decompression release. You don't want all fuel/air to escape.....only to unload the stalling hit the starter would take if it was not there. After the starter gets it spinning good, the "slightly open" time is less and less.....now almost up to full compression. Hint: It takes time for the fuel/air being compressed to leak off out the slightly open exhaust valve. Rotate faster and faster, less can get away every rotation with the same amount of cam button lift. Hope that makes sense. Rotation of the cam (faster than crank speed at some point) will sling the the weights out and the small disk will rotate (against the weak springs) via the 2 pins and retract the small pin........the full time run compression position. The disk has to rotate say some 90 deg between run (retracted pin button) and dead crank start positions. The extra metal limits the guessed 90 deg to say only 45 deg. Look at the last or lowest pic. Notice the 2 pins are NOT in the bottom of the V. If they were, the timing punch mark in the small disk would almost be covered as the disk rotated CCW some more. Look at the lower flyweight (easiest to see in the pic but both are excess material) and see the welded metal flyweight tab is rubbing the small disc. This tab needs to have the same profile of the main body stamped flyweight part. Not placed correctly in the jig when welded. I just scrolled back to your original post about the cam timing. The old flyweights looked off also but not as bad. With the pin constantly rubbing the it's rocker "tab", it would eventually grind out the softer tab and make a grove cut and then the compression release didn't work. Take this assy and do a thumb on the button test and rotate the small disk back and........the button should extend out of the cam and retract full below the shaft profile. They were stinkers. Cheap grease in the rear end. Heads not torqued down....head gasket leak......push out anti-freeze...some toasted or cracked the head. Purging the air after head work. Gasket maker drying out (got hard) and not sealing the rear facing drive shaft. Always feel the hoses for hot ones (means you have coolant flow). Stupid mini fuel tank...puked on hard steep hill climbs. Buried series snubber diode (opens=no fan=very BAD) buried in the wiring harness for the radiator fan. Soft 4WD diff lock up you never shift on the fly. Replacement cylinders the cam chain rubbed the Al inside the chain chute. Heat shields not deburred that cut into the O2 sensor heater wire and kills engine only in FWD gears....REV runs just fine. BTW, I own one. Bought a swimmer left by drunks at the river so they would not get a DWI----of course they was kind enough to leave the keys in the IGN overnight. I figured I knew all the bad stuff, so it was my entry level SXS. Never bought a vehicle that wasn't SICK. Old farm boy....fixed our own stuff. Gotta go.

I assume the new latest pics are the new cam and head assy????? It has a problem!!!!!!!!!!. Poor mfg process information (instructions and drawings) never really go away. They always pop back up like the turd they are. I was flown to Mexico for multiple "mistakes" and to T/S with a "fix and rework"---clean up the build information----and only to find the same problem pop up again 6 months later from the sister supplier, This problem was on both Yamaha Rhino and Hisun cam assys a good 5 years ago. We had Massimo. Another shop had Yamaha. They chased a mystery problem to the cam assy. My new cam assy arrived (with the same runability problem) in the newly uncrated unit.. I did the carbide burr air tool hand mill job on both sets. EXCESS WELDED WEIGHT GONE. Other shop has same problem. His flyweights had all the same machining, stamping marks...with welds identical.....the same sub supplier. My reworked flyweights were given away to fix the Rhino. Since you have the old cam, mark the flyweights to MATCH their wear "home" location. Remove and you should see the rub marks where the little disc hits the rear welded/attached weights. For the fun part: you can do it. 1. Hold the whole cam assy and put the button head pin that sticks thru further to the inside by the exhaust cam lobe DOWN. Gravity is your friend. 2. Put your thumb on the button-----should push in below the cam "shaft" profile----as in not the lobes profile----Rotate the disk and the mini cam will push up the button. 3. Reverse and the button will retract again into the cam shaft area. See how the system works. Flyweights pulled in by springs...sling out with rotation speed.....disengage the decompression pin.....at engine stop, the springs retract the weights but cannot due to the excess welded weight material profile rub with the small disk. 4. Pull out the small disk with the 2 flyweight engagement pins. 5. The "rod" attached (with the dogleg bend) is the minicam within the cam----used to push up the button pin that hits the extra tab on the exhaust side of the big valve cam. 6. With this pin out, the button can now fall into the hollow main cam center. Gravity----set down cam button down. If it falls to the center, no big loss. Just a pain to reinsert it into hits hole....ship in a bottle syndrome. 7. You should now see why the your adjustment is wrong. Rotation of the of the flyweights, rotates the small dime sized disk, which rotates the dogleg rod inside the hollow cam. 8. YUP, the end of the dog leg is what pushed the pin out further to engage the cam. BUT. if the small disk cannot fully rotate backwards, the button protrudes out too much and now does a compression release. 9. Your thinking now, why not just make the disc smaller in diameter........NOPE, not enough meat left for the pin hole wall thickness. 10. Reassy is just pushing back in the dogleg rod (with the decompression button facing down) and the punch mark up as used in the timing mark. BTW, use a small 6 inch scale to use as a straight edge to line up the cam bolts, alignment dimple and the cast timing mark in the head. BEN

You added some more info while I was typing, You have one of the flyweight sets that do not retract fully. This is an old problem form 5 years ago. Look at the 2 pins on the dime sized disk...........Notice the flywheel pin notches are slightly open.....not sitting in the bottom of the "v" groves. The flyweights are made of 2 parts.....the outer notched plate and the extra welded on weight tabs underneath. The small disk is holding the welded on weights about half open....inside circle is RUBBING against the dime sized disk on it's outer diameter. You need to grind out the excess material for the new one you bought. Storm front line coming. Making it short.......look at the used old flyweights.....check clearance/rub are.....if better trade the flyweights....later.

The inner bonded magnets are for the charging system. Nothing to do with the ignition unless the AC signal is used as a check by ECM to see if the engine is rotating. The outer metal tabs are just that....metal (steel) tabs for the pick up coil's internal magnet. Think of the keeper bar for a kids toy horseshoe magnet. The steel tabs react with the magnet inside the coil...sorta a make break for the magnetic flux.. The changing magnetic flux (starting with a change at the leading edge and a reverse at the trailing edge) generate the + and - pulse spikes. Your screw driver has some residual magnetism....it will probably pick up small screws. Try another tool. The ignition is a wasted spark system. The crank turn over 2 times per full stroke......since it doesn't have a cam sensor, just like an B & S lawnmower engine with points just run of the crankshaft....spark every rotation of the crank.....be it COMPRESSION or EXHAUST. Spin over with a timing light and check the painted timing mark (close to TDC). Coil resistance is in the ball park. At least it is not an open circuit. My old computer video player cannot play your videos....my bad I guess. I cannot view for a guess what is going on. Only set the timing marks per earlier reply. They will run a couple of teeth off, but poorly. You written description makes me think the exhaust valve is not adjusted correctly. This can happen if the valve was adjusted on the compression release button location....... and was out. This will result in the valve adjustment being wrong. Turn the engine over slowly by hand and bring the piston to TDC on Compression (both valves closed). Check for valve clearance. The decompression pin will be holding the valve slightly open. Turn backwards and feel for the valve to close again....this takes the load off the decompression cam actuator. Push the flyweights on the cam to the run position (rotates the small dime sized inner disk) and hold open while rotating to TDC AGAIN. This is what happens after the cranking speed increases after firing up and rotating to the idle speed. Check your clearance at the TDC this time. Adj if off. If you release the flyweights, they will sorta "stay" in the open position. The flyweight springs cannot physically push the exhaust valve open for decompression. There is a small inner cam that pushes the actual pin out before the valve rocker hits this decompression pin. Slowly rotate the engine backwards and the flyweights will fully retract. Slowly rotate forward and the exhaust halve will slightly open this time......lowering the compression pressure. These flyweights should "held" by the valve train pressure. Do a compression test again.......Should be at least 120 PSI with a correct compression gauge. Hope this explains better the decompression system.

Your pics are of the outer rim of the flywheel. The tabs in your pics are for the pick up coil......ECU senses the + and - pulses as the square buttons pass under the "face" of the PU coil. You have a "Missing Pulse" set up here. Others machines, like 4 wheelers, will only have a Single tab for a single cylinder and a V engine will have 2 with it's marks line up for IT'S TDC when they pass under the coil face. The pick up coil has a round bar magnet inside and wire wound around the bar magnet. Take the PU coil and put a small blade screw driver on the face...feel the pull of the PU coil internal magnet. MAGNETS Not shown in your pictures.......they are on the inside of the flywheel. They will be blocks (sometimes glued to the inside walls. Some had failures with unbonding but it will destroy the stator knuckles......these are used for charging the battery using the regulator....3 Phase......thus, these are the 3 yellow (white) wires that go to the Regulator. These have nothing to do with the timing tabs on the outer rim. Test the magnet(s) inside by taking say a 3/8" extension and roll around the inside.....will pull/stick at the gaps in the magnet bodies. You can see if the bonding has a crack.

Past experience for a random (as in your heat soak cycle-----engine hot and will come back to life again with some cooling) is the pick up coil. Next is the ignition coil. Use a spark gap tester and watch the spark quality and/or hit and miss or dead. The really OLD timing lights (60's) used just a dim neon tube. A weak spark would result in a really dim or non flash. Also, Snap-On sold a handheld spark voltage tester with flashing LED indicators and a thumb wheel voltage trip point selector. Lab scopes give a visual check if you know a friend who has one with the spark pick up clamp. STORY: I have had some pick up coils that would take forever to fail and then heal BEFORE you could pull the connector and connect an ohm meter to check for an open coil instead of the spec'd resistance. That one was solved by using a DPDT switch to check the resistance right as it died......could watch it "heal" again in less than 5 seconds. It had been thru a bunch of shops before me.