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.
Since I've seen some questions on this I took some pictures and will provide instructions on a valve adjustment for the UT400. This should be the same for the 550's and other various Coleman/Hisun single cylinder models with the cylinder slanted aft.
I have seen several people ask of it is really necessary, and read several reports of valves being out of adjustment from the factory. My valves were .004" intake, and .010" exhaust with about 5 hrs on the machine. I've seen different numbers thrown around for factory spec, but I decided to go with 0.005".
This is called valve lash. What is is is a gap between the rocker arm and the valve then the camshaft isnt opening the valve. Why does it matter? If it's too large the valve doesn't open all the way, if it's too small the valve dosent close. This can cause valve damage (overheating) as well as loss of engine power (burned fuel is going out exhaust rather than pushing the piston dow).
Tools required : 5MM Allen wrench, 10MM box wrench, needle nose pliers, flat feeler gauge set, rags
First you need to remove the fan cover on the passenger side. There is a cooling vent hose on the back side, remove the hose clamp and slide it off. From there there are 4x 10mm bolts holding the cover. The forward ones can be accessed from under the seat.
Next remove the spark plug from the drivers side. Carefully wiggle the spark plug wire off. Grip it as low as possible and give it a little twisting motion as you pull it off to help free it. Its a tight fit for a socket, but there is a sheet metal wrench in the toolkit that fits it. Unscrew the plug and set it aside. This allows you to spin the motor over freely with no compression to fight. When you reassemble this is a good opportunity to switch to an NGK iridium plug for better performance/less fouling DR8EIX)
Next you need to remove the intake and exhaust valve covers. The intake us the forward one. There are 3x 5MM Allen screws to remove. The Exhaust is the rear with 2x 5MM Allen bolts. Both covers have O-Rings instead of gaskets and are reusable. When you remove the rear be careful and use your rags as there will be oil that drips out.
Next up we need to spin the motor over to top dead center. Grab each rocker arm and give em a little wiggle up and down. Spin the engine over by grabbing the fan with your other hand. Spin the engine over until both rockers have some wiggle and are loose.
Once both rockers are loose slide the feeler gauge in like shown above. Try different feelers as needed to determine your starting spec. You should feel some drag but still be able to move the feeler without too much force.
If you need to adjust, use the 10MM wrench to slightly loosen the locknut, then with the correct feeler gauge in place, tighten the top square nut while wiggling the feeler in and out. Once you have it right you need to tighten the 10mm lock nut without moving the square head bolt. Once the lock nut is tight recheck the clearance.
That's it, button everything back up and make sure you have it all reassembled before running it again.
If you find this helpful give me a thumbs up or comment. If you have any questions or need more help let me know. If there's interest maybe I'll do some more of these
By Tim Barbero
I left my 2020 axis 500 UTV parked under the carport for about 6 months and when I went to start it recently a squirrel has built a nest under the throttle body and chewed through the efi harness. I stripped all the wires back and reconnected them with waterproof butt connectors. The problem I have is there is one blue wire with a red stripe coming from the main harness this wire has 5 volts dc showing on my multimeter but there are two blue wires with a red stripe coming from 2 different sensors on the throttle body. I looked through all of the bits and pieces of wiring left behind and there’s no indication that the three wires of the same color were all tied together. Any help with this issue would be greatly appreciated.