346xp lean running problem

[Simpsonsawshop]

This is a customers saw. About a year ago, I did a mild port job, muffler mod, base gasket delete, and new ring. The saw ran awesome for about 3 months then started acting like it had an air leak. Quick and dirty test with some carb cleaner indicated a leak in the inake boot area so I tore it back down and replaced the intake boot, pulse line, and factory metal pinch clamp with a worm clamp. Fast forward to now. It is doing the same thing, carb clean test shows a leak in the intake area but it passes a pressure and vac test with flying colors which suggests to me that the carb isn't sealing to the intake and my rubber block off is sealing it up.
What gives here? Is there a common problem that I dont know about? Warped plastic divider maybe? Gimme some ideas guys. This guy is an arborist and needs his saw back asap.

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[ucm931]

Sounds like you've got the the issue narrowed down to the boot and divider, just need to isolate it.
I'd remove the carb, seal the mouth of the intake boot with gorilla tape, then pressure and vac test again. The source of the leak should rear its head.

my .015 worth

 

[huskihl]

Is the little brass diffuser ring in place? Sometimes the boot can suck itself together if not. Or the plastic piece that the bolts thread into is warped

 

[beaglebriar]

Ya hafta be careful how much you tighten the carb bolts on them. Also check for binding around where the "worm clamp" was installed. Anything that's impeding movement/flex or is too wide could cause a tear. That's why the OEM metal clamp or a 385/390 clamp is the safest way to go IMO.

I'm building a 357 at the moment that had the intake updated at some point but whoever did it wasn't intelligent enough to clock the clamp left or right. The clasp was dead center on the bottom and caused an air leak at the cylinder base from hitting the crankcase which held the cylinder up just enough to make it leak a nut hair.

 

[cuinrearview]

While I've never had an issue, sometimes seating the cylinder seems like the flange on the partition could get wonky where it meets the ridge in the carb box. Maybe even on the wrong side of it.

 

[Stump Shot]

First thing that came to mind was what @beaglebriar said about the carb bolts. Once you've checked for damage, all they need is snugged up.

 

[Simpsonsawshop]

Ok, maybe I'm over tightening things. I will give it another go.

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[Ryan Browne]

I had one with loose carb bolts recently. Ran good, but with if you pulled up on the handlebar with the top of the bar against wood it would lean out.

 

[andyshine77]

Is she starving for fuel after it's been running at WOT, or the normal air leak idle issues?

 

[Simpsonsawshop]

It actually idles fine. It acts super lean at higher rpm and bogs bad on transition from idle to high rpm. I was 4.5 turns out on the H screw before I got any four stroking at all so something is obviously wrong.

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[Mattyo]

out of curiosity, have you tried a different carb?

 

[andyshine77]

OK you may have a tank vent issues. In fact there was even a production run that had fuel tanks that weren't drill out properly. So I'd drain the tank pull the fuel pickup and see if the van holds any vacuum, the if it holds any vacuum at all that may be your problem. Some actually open up the hole in the fuel tank behind the vent just to be sure. Others have added a separate vent like the one Echo uses.

And last but not least I've seen a few of these saws do this in the only fix was to use a different carburetor.

IMHO unless there is a large enough leak that idle is all goofy, using spray around the carb where it seals to the boot, will always have some effect on how the saw runs. At least this is what I have found. Either because the solvent is so thin it still makes its way past the sealing surfaces, or some is still getting in through the carburetor. matter what.

 

[popopboat]

Is it zama carb?
I had almost the same issue with my 359 and its H screw.
Turned out that its like that by the factory, so i replaced H nozzle jet and it fourstrokes like an old tractor.

 

[Mattyo]

if it did run fine, but now its not, sounds like a gunked carb to me.... I've chased all kinds of leaks before only to find its a gunked carb.

 

[Simpsonsawshop]

OK you may have a tank vent issues. In fact there was even a production run that had fuel tanks that weren't drill out properly. So I'd drain the tank pull the fuel pickup and see if the van holds any vacuum, the if it holds any vacuum at all that may be your problem. Some actually open up the hole in the fuel tank behind the vent just to be sure. Others have added a separate vent like the one Echo uses.

And last but not least I've seen a few of these saws do this in the only fix was to use a different carburetor.

IMHO unless there is a large enough leak that idle is all goofy, using spray around the carb where it seals to the boot, will always have some effect on how the saw runs. At least this is what I have found. Either because the solvent is so thin it still makes its way past the sealing surfaces, or some is still getting in through the carburetor. matter what.

I never even thought of the tank vent. This saw has a primer bulb and then the small white vent fitting with a hose routed up to the air filter elbow. Wondering if the vent is messed up now.

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[huskyboy]

Run the saw with the fuel cap cracked open and see if it runs any differently.

 

[Fullkip]

Have you pressure tested the carb and purge line. Fuel line also...

 

[av8or3]

I had a customers 346 drive me crazy. I kept checking it out and sending it out and he kept sending it back. A new case fixed the saw. Here’s what I EVENTUALLY found. I swear it didn’t leak or blow bubbles when I pressure/vac tested it. It would even idle great most of the time.

 

[Fullkip]

Glad you figured it out..I've been down that street on a 562. It was a sometimes leak . The bearings have seals in them, this saw was leaking between the race and crank. It only leaked when it was warm. I was pulling my hair out.
Saw tuggers are hard on bearing pockets I've had some 372s with bad pto pockets.

 

[av8or3]

It never occurred to me that that was what caused it. I figured they just let it cool down a bunch with a tight chain. It’s a tree service saw. Judging by other saws from the same company they ride em hard and put em up wet.