Help on a 372xp

[fin460]

A local friend got a great deal on a blown top end nonxtorq 372xp.

The saw is really low hour, and came with a lean seized A/M top end. I happened to have a take off OEM piston and cylinder.

I pressure and vac tested and found massive air leak where the intake boot seals at cylinder under clamp, decomp valve was leaking bad, and the spark plug was leaking but it was loose, probably wasn't part of the problem.

I checked the fuel line and it was in great shape. I pressure and vac tested through the impulse line.

I'm not sure what else to check on the fuel system, I need to learn more there.

Put the saw back together, new intake boot, sealed off the decomp, and new spark plug that sealed. passed a good pressure and vac test.

Walbro carb.

Saw started on third pull, idled and rev great. Finally got a chance to cut with it a couple days later, and I couldn't get it to richen up. I was against the H limiter. Went and got my tach, saw was turning upper 14k WOT Saw idled fine like there was no air leak, but I haven't ruled it out again.

I trimmed limiter tab and it wasn't enough. I finally trimmed the tab off all the way and went a full turn past the old limiter tab.

Saw finally then was 4 stroking running rich 9-10WOT, so I leaned out to 11,500WOT and was still burbling heavy but would clean up in heavy cut. I made several cuts checking the tach along the way.

Saw kept gaining RPMs, It finally climbed up to 13K WOT. I ran out of wood to cut, and noodled a couple pieces and decided to quit and pressure and vac test before I went further. Cylinder seemed warm, and when I shut the saw off the intake started making popping noises.

I am super green to working on saws, I sure enjoy it, but it makes me nervous to work on saws for other people, I want to be confident in the saw when I turn it back over.

Any conversation is helpful, I will pressure and vac test again, but is there anything that I'm doing wrong jumping out.

Thanks.

 

[RedFir Down]

Saw kept gaining RPMs, It finally climbed up to 13K WOT. I ran out of wood to cut, and noodled a couple pieces and decided to quit and pressure and vac test before I went further.

Was the saw gaining RPM because you were leaning it out? When a saw warms up it will run a bit leaner than when it is cold.

when I shut the saw off the intake started making popping noises.

Can you explain this a little more Justin?

 

[Mattyo]

Fin, you do a lot of pressure testing! ... one thought that comes to mind, if you notice or suspect an air leak in the vicinity of the intake, spray some carb cleaner on the intake boot while the saw is running... if it dies, you have found your leak. If you are questioning the seals, seems silly to me to chronically test for leaks when you have basically figured out that the seals are fine. ie, the problem lies elsewhere. too much air also means too little fuel.

it sounds like you are well on your way to getting this running reliably ...so I doubt I'm helping much...

 

[cus_deluxe]

My 288 was doing something similar. When held at WOT, it would hit 11,500, then continue to climb the longer i held the throttle. It would climb to 12,500 or more until i let off. Took carb off, removed jets, blasted all orifices with powerfoam, reassembled and problem solved. Thinking there was a bit of debris on end of hi jet that was obstructing flow. Not sure about the popping noises though...

 

[Chainsaw Jim]

The bearings can fool you. They can feel tight by hand but wobble under more pressure causing a slow climb in rpm at wot. The more they wobble the more the air can leak.
The popping noise may have been bearing related if a bad bearing can get hot enough to ignite left over fuel in the crank. I don't know if that's even possible, but my imagination seems to entertain the thought.

 

[fin460]

Was the saw gaining RPM because you were leaning it out? When a saw warms up it will run a bit leaner than when it is cold.


Can you explain this a little more Justin?

Like hot grease poppin, almost sizzling

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