038 driving me nuts.

[stretch5881]

I've been working on a buddy's 038. Symptoms are, it starts and idles fine. When I would tag the gas, it would almost die. I changed the fuel line, filter, impulse line, intake boot and rebuilt the carb. Same result. I put a new carb on and it ran great for 10 minutes, and we are back to the original symptoms. I run it on it's side with the fuel cap loose, same result. I changed the coil and spark plug, same result. Try without the air filter, same result.
Any suggestions?

 

[sixonetonoffun]

I'd recheck the impulse and choke first. Maybe a new spark plug just to eliminate that too.

 

[stretch5881]

I'd recheck the impulse and choke first. Maybe a new spark plug just to eliminate that too.

Nope, same result. Thanks.

 

[Nutball]

How about a video so we can hear it. Does it need more fuel during the transition? Does it reach full throttle? Does it idle after the issue occurs? Maybe richen the idle?

 

[stretch5881]

I wouldn't know how to do a video. It idles great both before and after trying to accelerate. It sounds like it starves for fuel when I tag the gas. It never gets close to wot. I have richened both high and low with no difference in acceleration.

 

[Nutball]

If it never gets close to full rpm, maybe there's a plugged spark screen in the muffler? I assume you have seen that the intake side of the piston is intact right? Being an old saw it may have seen enough use to wear down and break off a chunk of the piston skirt ruining the intake timing. I doubt it though.

I wonder if dirt has gotten into the check valve in the main nozzle.

 

[ChipsFlyin]

Did you do the welsh plug and screen when you did the carb? Crap gets in there.

 

[stretch5881]

If it never gets close to full rpm, maybe there's a plugged spark screen in the muffler? I assume you have seen that the intake side of the piston is intact right? Being an old saw it may have seen enough use to wear down and break off a chunk of the piston skirt ruining the intake timing. I doubt it though.

I wonder if dirt has gotten into the check valve in the main nozzle.

Muffler screen is clear. Piston is intact. I will disassemble the carb tomorrow. It wouldn't be the first time I found machining waste in a new carb.

 

[stretch5881]

Did you do the welsh plug and screen when you did the carb? Crap gets in there.

It's a new carb.

 

[Stem]

fuel tank vent? did you use OEM hoses & filter?

 

[drf256]

Check the crank key to make sure it didn’t shear-costs you nothing.

Did you vacuum test the saw?

Take a look at the carb, but 10 min of “normal” makes no sense for that.

Try different fuel mix. I’ve been burned by that myself. Change plug, again. What does current plug look like? Could it be fouled?

Check intake boot fit up, especially if you went AM on it. The 038 has that weird 90* intake and any lip there can catch fuel and cause a bog when you goose it, especially if you have a vac leak and need to run the saw fatter at idle.

Last but not least, pull the jug and see if the intake skirt of the piston is chewed up or has excessive clearance.

When they get like this, sometimes there is no choice but to rip them apart fully. You eventually find the culprit.

 

[stretch5881]

fuel tank vent? did you use OEM hoses & filter?

I had checked the tank vent and also ran the saw on its side with the tank cap loose and had the same result.

 

[stretch5881]

Check the crank key to make sure it didn’t shear-costs you nothing.

Did you vacuum test the saw?

Take a look at the carb, but 10 min of “normal” makes no sense for that.

Try different fuel mix. I’ve been burned by that myself. Change plug, again. What does current plug look like? Could it be fouled?

Check intake boot fit up, especially if you went AM on it. The 038 has that weird 90* intake and any lip there can catch fuel and cause a bog when you goose it, especially if you have a vac leak and need to run the saw fatter at idle.

Last but not least, pull the jug and see if the intake skirt of the piston is chewed up or has excessive clearance.

When they get like this, sometimes there is no choice but to rip them apart fully. You eventually find the culprit.

I will recheck all your suggestions. I will blow out the carb first and vacuum test. If no change, then it is a complete teardown again.

 

[stihl_head1982]

Is the choke on this saw's air filter -- a flap inside the air filter? If the filter is old the spring could be weak, or it could be the spring is off the mechanism that
makes the choke operate. Several Stihl saws have this flap/choke mechanism built into the filter. Sometime the flap inside the filter can malfunction and cause a
problem.

 

[stretch5881]

Is the choke on this saw's air filter -- a flap inside the air filter? If the filter is old the spring could be weak, or it could be the spring is off the mechanism that
makes the choke operate. Several Stihl saws have this flap/choke mechanism built into the filter. Sometime the flap inside the filter can malfunction and cause a
problem.

Problem remains with air filter removed.

 

[stretch5881]

OK, here we go. I did all the normal diagnostics. All checks out good. EXCEPT while doing the vacuum test, when it got to about 3 in. vacuum, the new intake boot sucked flat.
I have never payed attention to the intake boot during vacuum testing because I never had this issue before. I don't know if that's normal. The boot is new AF.

 

[Moparmyway]

Get an OEM boot

 

[Moparmyway]

I've been working on a buddy's 038. Symptoms are, it starts and idles fine. When I would tag the gas, it would almost die. I changed the fuel line, filter, impulse line, intake boot and rebuilt the carb. Same result. I put a new carb on and it ran great for 10 minutes, and we are back to the original symptoms. I run it on it's side with the fuel cap loose, same result. I changed the coil and spark plug, same result. Try without the air filter, same result.
Any suggestions?

Stretch,
You have been here since Dec 2017.
How many times, in how many threads, have you seen members try to overcome the "AfterMarket blues" ?
I have seen it over and over, both here, and on saws that I get through my place. Aftermarket sucks. I will only use them kinds of parts in a hard pinch. OEM is worth the wait for the quality and performance they offer over the aftermarket. Now, there MIGHT be an arguement here or there where AM parts are OK to use ................. but I will leave that discussion for those who have more time on their hands. I know where I stand.

What OEM parts did you use, and what AM parts did you use ?

 

[drf256]

OK, here we go. I did all the normal diagnostics. All checks out good. EXCEPT while doing the vacuum test, when it got to about 3 in. vacuum, the new intake boot sucked flat.
I have never payed attention to the intake boot during vacuum testing because I never had this issue before. I don't know if that's normal. The boot is new AF.

That’s not normal. Sounds like the saw gets warm and the already too soft AM boot gets softer. Probably comes off WOT to closed throttle plate and sucks boot closed.

Not sure if OEM are NLA.

 

[stretch5881]

Stretch,
You have been here since Dec 2017.
How many times, in how many threads, have you seen members try to overcome the "AfterMarket blues" ?
I have seen it over and over, both here, and on saws that I get through my place. Aftermarket sucks. I will only use them kinds of parts in a hard pinch. OEM is worth the wait for the quality and performance they offer over the aftermarket. Now, there MIGHT be an arguement here or there where AM parts are OK to use ................. but I will leave that discussion for those who have more time on their hands. I know where I stand.

What OEM parts did you use, and what AM parts did you use ?

Carburetor, fuel and impulse lines and carburetor boot are aftermarket. Seals are oem. The only problems I have had with AM have been seals and the occasional carburetor. AM pistons, I only use Meteor with Caber rings.
The guys I work for are usually in their 70s and 80s. They can't afford oem. They just need their saw running for firewood.