Chainsaw won't idle after wot

[Rx7man]

Perhaps you can spray something like carb cleaner around the intake, etc while it's running to see if that changes it's characteristics.

It seems the symptoms have changed..
I'd check for pinholes in the fuel hose (I know you said you checked it twice).. You probably won't notice an air bubble at WOT, but at idle it can really mess things up.. worst part about them is sometimes they won't leak fuel out to show you where it is... Metering lever would be something I'd look at again, maybe raise it a smidge

 

[67L36Driver]

Typically 'dies after WOT' is a lean idle mixture.

Open the low side 1/4 turn and check.

 

[jdvsn83]

Perhaps you can spray something like carb cleaner around the intake, etc while it's running to see if that changes it's characteristics.

It seems the symptoms have changed..
I'd check for pinholes in the fuel hose (I know you said you checked it twice).. You probably won't notice an air bubble at WOT, but at idle it can really mess things up.. worst part about them is sometimes they won't leak fuel out to show you where it is... Metering lever would be something I'd look at again, maybe raise it a smidge

I'll check the fuel hose with a vacuum/pressure pump too. Sprayed carb cleaner around the intake: the speed didn't change.

 

[jdvsn83]

Typically 'dies after WOT' is a lean idle mixture.

Open the low side 1/4 turn and check.

Hmm nope, I tried opening low side from lean to rich (lots of smoke at idle) and then it started to rev when hot. I'll vacuum and pressure test the engine, lines and tank and will post the results here.

Thank you all!

 

[jdvsn83]

Guys, vacuum and pressure test done. Crank seals and cylinder gasket are perfect. I did the test cranking the engine too.

Impulse line and fuel line vacuum and pressure tested and both are ok.

Fuel tank/breather tested the same way. It holds pressure and won't develop vacuum.

I'm afraid it has a crack somewhere and it will show only when hot...

 

[Chris-PA]

What carb is on it?

I'm wondering if a bad check valve is giving a inconsistent seal. Every time you go to WOT the valve must open, and close again each time you return to idle. If it sometimes does not seal the idle may be a problem.

 

[jdvsn83]

What carb is on it?

I'm wondering if a bad check valve is giving a inconsistent seal. Every time you go to WOT the valve must open, and close again each time you return to idle. If it sometimes does not seal the idle may be a problem.

Walbro WT782A JAPAN

 

[SEAM]

Did you check the fuel tank breather? Sounds like a vacuum building up in the fuel tank during use... Try opening the tank lid next time it dies - if you hear a swishing sound (air going into the tank) you found the problem.

Another possible cause: A bad primer bulb valve (if any). After priming the fuel in the return hose could be drawn back into the carb followed by air from the tank after some time.

 

[jdvsn83]

Did you check the fuel tank breather? Sounds like a vacuum building up in the fuel tank during use... Try opening the tank lid next time it dies - if you hear a swishing sound (air going into the tank) you found the problem.

Another possible cause: A bad primer bulb valve (if any). After priming the fuel in the return hose could be drawn back into the carb followed by air from the tank after some time.

Thank you! No primer in this Walbro carb. I vacuum and pressure tested fuel tank and breather.

 

[jdvsn83]

Ok, I did some cuts today and the problem didn't show up. I shortened the fuel line in the tank side because it was too long. Filter didn't get stuck before shortening it, but maybe the line collapsed intermittently when running the saw.

Or maybe the air leak stopped after reassembling the entire saw... Who knows... Crank seals and cylinder gasket are in perfect shape.

I'll try it at work and will post the results.

Thank you all for your help.

 

[jdvsn83]

After some heavy work I can say the problem was solved. No more erratic idle and it idles after WOT too.

Maybe an air leak in some part i couldn't test with the pressure/vacuum gauge...

Thank you guys.

 

[Shedge]

Hello guys,

This is my first post. I am trying resurrecting this thread because I have exactly the same problem described by the OP, and can't find any way to solve it.

I see he solved the problem but it's not quite clear to me how exactly he managed to get it working.

Like him, I tried pretty much anything and carb & engine seem OK. The same goes for tuning. If I lean the Low the problem is less severe, but I get also sag during acceleration. It's definitely not a problem with tuning.

Any ideas?
Than you

 

[Pioneer]

I have had the same problem with some saws, and it's usually too rich on the high side that causes it. What happens is the saw will run at WOT but as soon as you release the throttle you now have a crankcase that is loaded up with that rich mixture and it dies at idle before it can clear itself. Pulling it through a few times usually clears it and it starts. With a proper WOT mixture the saw should drop just slightly below it's normal idle speed after the throttle is cut, and then pick up a bit and settle into a normal idle.

 

[jdvsn83]

I have had the same problem with some saws, and it's usually too rich on the high side that causes it. What happens is the saw will run at WOT but as soon as you release the throttle you now have a crankcase that is loaded up with that rich mixture and it dies at idle before it can clear itself. Pulling it through a few times usually clears it and it starts. With a proper WOT mixture the saw should drop just slightly below it's normal idle speed after the throttle is cut, and then pick up a bit and settle into a normal idle.

Yes, that's true. Not on this particular saw/case, but it happens sometimes with too rich high speed condition.

 

[jdvsn83]

Hello guys,

This is my first post. I am trying resurrecting this thread because I have exactly the same problem described by the OP, and can't find any way to solve it.

I see he solved the problem but it's not quite clear to me how exactly he managed to get it working.

Like him, I tried pretty much anything and carb & engine seem OK. The same goes for tuning. If I lean the Low the problem is less severe, but I get also sag during acceleration. It's definitely not a problem with tuning.

Any ideas?
Than you

Check your inbox for details. Finally it was solved with a different metering diaphragm.

 

[diesel&coffee]

I have had the same problem with some saws, and it's usually too rich on the high side that causes it. What happens is the saw will run at WOT but as soon as you release the throttle you now have a crankcase that is loaded up with that rich mixture and it dies at idle before it can clear itself. Pulling it through a few times usually clears it and it starts. With a proper WOT mixture the saw should drop just slightly below it's normal idle speed after the throttle is cut, and then pick up a bit and settle into a normal idle.

THANKS. I have a MS660 ( yes new to tuning chainsaws ) and was wondering that very thing today. Was simply revving / and a few cuts / and when cutting throttle it would drop / bog for 3 - 5++ secs and come back to idle. This answers a basic question.