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jdlmodelt

1988 Foreman 350D high compression question

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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

 

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Welcome to the forum. How does the spark plug look after running it? Did you do any re-jetting to it? I'm at a lower elevation but back in the day I was running a 12:1 in my 350 on pump gas without issues. Of course, back in the day we had better fuel also. 

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Check page 4-16 of the manual for high altitude operation 

Below 5K ft ASL use stock main jet #142

between 3K-8K ft ASL use #132.
I operate 3K-5K and use #138.

 

part number 99101-kpe1380

search for 99101-kpe and then whatever jet size like 132.5 will be 99101-kpe1325

 

dont know if that’s the cause of your ping but when my 450S and Ranchers were pinging turned out to be a dirty carb

 

 

 

590482D9-B352-47FC-BDFB-8727BC69BB45.jpeg

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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.

 

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Yup there’s a better explanation for the primary adjustment in the manual than what I could do. And it usually takes me a few trials to tune the carb—engine gets too hot for me to get the pilot screw the way i like it.

 

also—did you change the choke valve? Does the engine choke right away when you activate it? If so it’s probably ok

Edited by Goober

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3 hours ago, Goober said:

Yup there’s a better explanation for the primary adjustment in the manual than what I could do. And it usually takes me a few trials to tune the carb—engine gets too hot for me to get the pilot screw the way i like it.

 

also—did you change the choke valve? Does the engine choke right away when you activate it? If so it’s probably ok

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. 

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Be sure to wash your hands for 10 minutes after working on the Polaris. Don't get any poo on your Honda! 

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carb sounds like it’s set up pretty good; how’s your air filter—pretty old? If so, might be collapsing and restricting airflow.


Did you replace the header coppers? I put new on mine when i painted header with 2000F paint. Also Consider checking for an exhaust leak near the header joint. Usually these don’t make a ping sound, but could be worth a check.

7B05337E-1BD4-4646-A7D3-395B4D324701.jpeg

Edited by Goober

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18 hours ago, jdlmodelt said:

it makes what I would describe as a chirping sound.

 

 

I can't say I have heard it on a 350 but the early 300s was bad for a chirping sound at idle and it was the cranckcase breather tube that did that.

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