jdlmodelt

the compression new on these is 181-210psi. I think you indicated you have from 60-80psi?

The numbers you posted for compression are pretty low for hot or cold. The carburetor isn't making your compression go down when the engine is hot. There is something mechanical that causes your compression to drop when hot. It's either as someone else indicated, decompression mechanism holding the exhaust valve(s) open, or scoring on your cylinder wall and piston, or some other mechanical issue with your valves. At this point, you would spend less time if you just pulled the top end off unless you are able to determine the decompression mechanism is the culprit.

Does this model have the fuel pump that ticks when its pumping? My fuel pump is fairly audible and It was a semi continuous to semi random ticking rythm. The decompression interfering while warm/hot makes sense with regards to the compression. The only other thing I can think of is do a top end overhaul. Sounds like you'll see things in there that you can't see right now. Mine had cupped rockers where they ride on the cam. Cam was fine. My top (intake) side of piston and cylinder were scored due to overheating or lack of lubrication. Now, new rockers, bored out 0.5mm and new Wiseco 10:1 piston and she runs.

it makes what I would describe as a chirping sound.

Haha! Agreed. I've never been much of a Polaris fan.

The choke works great. This engine starts in single digit F temperatures great. I did notice I've lost a slight bit of my power after that adjustment I did on the metering rod to butterfly valve, so, I will play with that some more. I had to put my own project aside to work on a guy's 2002 polaris 500 ATV. It acted like it had jumped a tooth on the cam chain. It was lacking some compression and backfiring when attempting to start. It ran fine when last parked. Turns out the spark plug threads in the head were down to 2 or 3 threads and the spark plug was just wobbling around in the socket area. I'll need to do a helicoil repair on that one next week. Then I have to rebuild the top end on Dad's Hisun 500. That UTV has been a total POS. But we keep it limping along.

Does this model have the fuel pump that ticks when its pumping? My fuel pump is fairly audible and It was a semi continuous to semi random ticking rythm.

This was the case with my 88 TRX350D Foreman. Rocker surfaces that ride on the cam were so worn they were cupped. I was fortunate that everything else was still within spec. I replaced rockers and installed a new piston 0.5mm oversized and it runs like a champ now. And it was super noisy no matter what I did to adjust the rocker lash. Now its super quiet.

So I picked up a 135 as that was what the shop had in their assortment of jets. I get home. pull mine out and observe with a magnifying glass and wouldn't you know. Mine already has a 132! Lol! I did readjust the jet metering tube synchronization with the butterfly valve so the metering tube is resting on the metering jet at idle. When I adjusted the synchronization with the idle screw all the way off while overhauling the carbureator, I had the two opening at the exact same time, however, after installing, the idle screw has to be advanced a few turns to get to engine idle, and consequently, lifts the jet meter tube allowing more fuel. This may have been the contributor to the plug running rich and mostly at idle which should only be getting fuel through the air/idle adjustment screw? It's my understanding the meter jet and rod are the acceleration and high idle fuel supply? Hope I'm making sense.

Hello, I recently had my 88 Foreman 350D bored out 0.5mm and installed a Wiseco 10.25:1 piston. I'm running 91 octane fuel as that's the best I can get here in Colorado. I live at 6400 fee elevation. There is what I would describe as a chirpping sound at low rpm loads. I'm wondering if this is engine pinging and if anyone has determined a way to adjust the spark timing as this is my machinist's recommendation? Other than the chirpping sound, the engine is super torquey and strong. Thanks, James