357xp air leak at throttle screw?

[edrrt]

So my 357xp starts and ran well but just sounded a little leaner than it should at idle and I couldn't tune it out. Dripping carb cleaner on the throttle screw. A few drops and it will bog down and a direct spray and it will quit.



I took the carb about and I'm wondering where do I start to try and fix this. Do you just take the butterfly valve out and is there an o-ring in there or something?



This saw got straight gassed by my dad. I swapped the top end for a Chinese one first with the intention of putting an oem on it if all was well. It seems all was not well. I guess I should buy a vac tester... or a 372 lol.

The compression is still 152psi... but I see marks. At least it's only a 30 dollar top end.

I will order a vac tester. Where do I start with the carb?

 

[sean donato]

Toss it and buy a new one. Shaft or bore is worn on it.

 

[SteveSr]

So my 357xp starts and ran well but just sounded a little leaner than it should at idle and I couldn't tune it out. Dripping carb cleaner on the throttle screw. A few drops and it will bog down and a direct spray and it will quit.

View attachment 891107

I took the carb about and I'm wondering where do I start to try and fix this. Do you just take the butterfly valve out and is there an o-ring in there or something?

View attachment 891108

This saw got straight gassed by my dad. I swapped the top end for a Chinese one first with the intention of putting an oem on it if all was well. It seems all was not well. I guess I should buy a vac tester... or a 372 lol.

The compression is still 152psi... but I see marks. At least it's only a 30 dollar top end. View attachment 891109

I will order a vac tester. Where do I start with the carb?

ALL carbs will leak slightly at the throttle and choke shafts. Usually not a big deal unless excessive. Sounds like you have another air leak somewhere else...

 

[J D]

Check the impulse line, I've seen several with pin holes in them & it's right below where you're spraying. They're also prone to leaking where the boot attaches to the cylinder, does it have the updated metal clamp?

 

[edrrt]

Check the impulse line, I've seen several with pin holes in them & it's right below where you're spraying. They're also prone to leaking where the boot attaches to the cylinder, does it have the updated metal clamp?

It had a bigger air leak. Foolishly the carb diaphragm/ gaskets were not installed correctly. That was the first leak I found. After correcting that the saw still sounded lean.

Spraying around the cylinder base, intake boot, impulse line, carb... nothing.

Dripping on the throttle screw definitely bogs it down. Spraying it stalls it. Is that normal?

It could sound off just because the piston is damaged from the diaphragm gasket leak. I have an extra hyway piston I could try. Amazon sent me two last time by accident.

I'd just like to get it right this time.

Is there anything else I should check? Would you normally be able to stall a saw spraying the throttle screw? I guess I could try it on one of the other saws.

 

[edrrt]

I just checked the 346xp and it does the same thing so I guess that is normal.

Maybe it was just the top of the carb not being sealed right. Diaphram upside-down, no gasket. Ran all out for 2 days straight like that pretty well.

Anything else to check or just put it back together and do a vacuum test?

 

[J D]

Auto decomp was a problem on the earlier ones, if it previously had one the line back to the crankcase may not be properly sealed. Check inlet boot for the updated metal clamp (plastic ones came loose & leaked). When you put a gasket in the carb make sure it has the hole to allow the outside of the diaphragm to vent back to the inlet. In those carbs the metering is biased by inlet pressure not atmosphere. That system has it's own issues but I'd worry about any possible air leak (ie vac/pressure test) before delving into that

 

[Huskitoter]

Some aerosol may have been sucked into the intake during your test.

Did you put an AM carb kit in it?

 

[cuinrearview]

I see a decomp button in your pic so the automatic setup is ruled out. The other known leak area is the plastic intake clamp. Is yours this style I can't quite tell in the pics?

 

[edrrt]

That's a good video thank you for that.

It has the metal clip.

I'm going to put the old OEM cylinder back on cleaned up with a new extra piston that I have to test it.

Vacuum tester should arrive on Wednesday. How do I connect it to the saw to pull a vacuum? The impulse line?

 

[J D]

How do I connect it to the saw to pull a vacuum? The impulse line?

Correct.
A piece of inner tube between the muffler/cylinder & carb/boot is a good way to seal it.
Spray bottle of soapy water will help you find any leaks. Check around the plug & decomp first as they often don't seal perfectly. Teflon tape on the plug works well & a bit of grease in the decomp or pulling on it while testing

 

[edrrt]

That's a good video thank you for that.

It has the metal clip.

I'm going to put the old OEM cylinder back on cleaned up with a new extra piston that I have to test it.

Vacuum tester should arrive on Wednesday. How do I connect it to the saw to pull a vacuum? The impulse line?

Correct.
A piece of inner tube between the muffler/cylinder & carb/boot is a good way to seal it.
Spray bottle of soapy water will help you find any leaks. Check around the plug & decomp first as they often don't seal perfectly. Teflon tape on the plug works well & a bit of grease in the decomp or pulling on it while testing

I put it all back together and a little bit of carb cleaner down by the impulse line will still stall it. I have taken the boot off and inspected it, check the impulse line carefully, I don't see any source of the leak. Is there anything else I can do. If you spray soapy water around the area while it's running will you see it being drawn in or bubbles being pushed out?

 

[edrrt]

I found it.

There's a large sucking noise and soapy Bubbles when moving the piston coming out between the nipple for the impulse line and the rubber intake boot.

 

[edrrt]

I found it.

There's a large sucking noise and soapy Bubbles when moving the piston coming out between the nipple for the impulse line and the rubber intake boot.


Looks like then boot where the impulse line enters wasn't seated in the cylinder right. Ant tips for seeing it does?

 

[cuinrearview]

Mount it to the cylinder before putting the cylinder on.

 

[edrrt]

Mount it to the cylinder before putting the cylinder on.

Done.

Runs normal finally.

Something I was curious about but couldn't find any first-hand reports of is whether there was a REAL performance difference between the 47mm after market cylinder VS the OEM.

After swapping between them just now... YES. HUGE.

The OEM feels like 2x the saw. Much zippier. Def worth it.

 

[pbilly]

mod the muffler its like a totally different saw after

 

[edrrt]

mod the muffler its like a totally different saw after

So I got the vacuum tester and I had a very slight leak. Maybe about 2 lb per minute. I checked the decompression valve with a little carb cleaner and it stalls. Is it normal for the decompression valve to do that or does that indicate that it's likely bad?

 

[Huskitoter]

You can try putting the valve in a vice and give the mushroom a couple good taps with a hammer.

Someone posted the hammer trick a while back, and it worked for me on one that I had replaced because it was leaking. I felt less compression when pulling the cord when it leaked but it would seal if I pushed the valve in and rotated it.

 

[sean donato]

It's a 50cc saw, block the decomp off. Never had a need for it on my 346 or 359.