2010 Massimo HS500 (carb model) Help

[matthejl]

Quick history:

Bought it about a month ago and when I test drove it, it ran good. Loaded it up and took it home. Owner said it had been sitting for a long time, but was "just serviced". It only has 500 miles on it total. Drove it around and found out the charging system wasnt working...so had to charge the battery once every week and a half or so. One day my daughter was driving it and it died. I couldnt get it to start again and I noticed there was no fuel in the filter...I first checked pulse/vacuum line to make sure it was sucking and it was. So I replaced the fuel pump with one I found local...which is for a large riding lawn mower...and it worked. Engine started and ran, but struggled at low speed immediately following running it at higher speed. It would bog when decelerating. I have also noticed now that it will backfire some on decell and die.

 

In the meantime, I went ahead and installed new stator and trigger coil assembly to get the charging system working again (that was an issue because it would not start at all after that...but eventually found that the trigger coil was wired backwards in the plug from the factory). I have also set valves, but I set them to .005 (intake) and .007 (exhaust)...per the manual. But what is weird is the manual states its mainly for the 700 series, but "can" be used on other models. On the front it says 500/600/700. I have noticed that the most common setting seems to be .005.

 

Anyways it still has the issue to me that seems like its running lean. Not full power now, struggles immediately running it faster, and will die and pop some on deceleration.

 

My main problem now is that it wont get to higher rpms as fast as it did when I first bought it. It struggles on deceleration after running near top speed.

 

Things I have done:

changed fuel pump

replaced stator / pickup coil

thoroughly cleaned carb (twice)

set valves to .005 and .007 (is .007 too loose for exhaust?)

 

anyways it seems to have a lean problem, and wondering if you have any suggestions on what to check.

 

Thanks

[Ben1098]

Pull spark plug and check the tip color.  If it is lean, it will be WHITE after a run.  Correct F/A mix will be a light rusty tan color.  Too rich F/A mixture will be fuzzy black (Wet fuzzy if real bad and fouls easily). Too lean will be a blistered white tip....bad for engine.   Start here...read the plug.

Do a compression check.  Compression gauge is nice but a simple finger covering the spark plug hole while cranking (WOT) tells the tale.  Your finger will "blow off" with a nice pop (might even get an air flow burn-heat up fingertip) with good enough compression.

A shot of starter fluid will "help" overcome a lean burn starvation problem.  Pull airbox lid and give a short burst to the air intake (filter).  If lean, engine should recover with the extra fuel source.

 

You have the hanging fuel box that is just a gravity feed fuel supply.  People forever hook them up wrong with the 2 fuel and single crankcase pulse lines.  There is an excellent post (color) on this forum that shows the diagram for the tubing connections.  The fuel pump has the pulse line that moves the diaphragm that pumps the fuel thru the internal check valve flaps.  The other 2 ports are IN (from fuel tank) and OUT (to the hanging fuel box).

The hanging fuel box has an IN (from fuel pump), and 2 OUT ports.  The excess fuel is returned to the unit's under seat fuel tank and holds the fuel level in the hanging tank to about HALF FULL.  The other OUT is the fuel line to the carb.  The height of the fuel level ABOVE the carb bowl is what creates, by gravity, the pressure required to fill the carb bowl.  I never liked this system as it worked fine on level ground but climbing out of a wash, the tank "height above the carb=pressure" is reduced as the machine is tilted to the sky on climb out......exactly when your fuel demand is the highest......fuel in the carb bowl drops resulting in a lean powerless hard climb out of the wash or steep up hill grades.  I would sub a low pressure electric fuel pump on units and golf carts and have the added BONUS of having a "filled" carb at startup.......none of this crank.crank.crank.crank to finally get fresh fuel after a heat soak or sitting for a day or 3.

Procure (bike shop sale item) or make a "test tank".  It is just a plastic bottle/ shut off valve/fuel line hose that is hung above the carb and looks like an drip (medical) IV......without the infusion pump.  Gets around any fuel delivery problems from diesel "mix", water slop from phase separation in OH fuel, all the way to the carb fuel nipple. 

Another problem is fuel line/tubing "crumbs" that break off on pulling and reinstalling old hose can clog or "restrict" the flow also.  Blockage being between the carb fuel IN nipple and the float assy internals.   EXAMPLE:  A person bought a new plastic gas can....did NOT look inside before using.  Ford 2000 could run all day BUT only last 3 minutes with a little 5' Bushhog.  He let it "cool down" and it would restart only to repeat the death throes.  He had $$$$$$$$$$$ in fixing the electrical system only to find out it fixed nothing with using the Bushhog.  Plastic drill pigtails from the drilling of the gas can's vent hole (old style can) was poured in to the Ford's fuel tank (gravity feed system) and restricted the fuel flow at the water bowl filter.  OUCH!!!!!!!!

Happy Hunting.