Stihl 025,air problem?

[shadycon]

Hi everyone, As you see I just registered. I was looking for an answer to my problem and this site kept popping up. So a little history: Saw is about 20 yrs. old. 2 yrs. ago it just would not wind up and barely would run. Took it to the shop and they replaced the carb. and crank seals. Ran good until about 2 mo. ago. Now it starts fine. Runs like it should until it warms up, then it wants to run wide open, It will slow down after a few seconds and shut off. Now it will not start until it is cold again. It seems the common opinion is it is sucking air. I do not have anyway to do vac. test. What would be a good place to start looking for the problem?

[joe_indi]

I would look at the simplest reason that could cause this problem, which is the pickup body (fuel filter in the tank). A partially blocked pickup body would cause this.
Also have a look at the air vent on the tank. In the case of your 025 it should be a small bit of tube with a screw in it, located on the left side of the air filter

[shadycon]

Thank you for your reply; I have checked fuel system and vent, carb is tight, air cleaner is clean. I guess it's time to look deeper.

[joe_indi]

Engine Pan screw(s) could be loose
Impulse hose might be loose on its nipple on the handle housing
Impulse hose might be blocked
Strainer in the carb  might be blocked
Manifold might be torn
A seal might have dislodged partially
A leak in the fuel hose
If its none of the above, you will need to do a pressure test (not compression) followed by a vacuum test

[Al_Smith]

Sounds to me like a seal going out .What happens is the seal does okay when it's cold but heats up the more the engine runs eventually causing a massive air leak which in effect starves the cylinder for fuel .

Usually it's the clutch side seal .It's the one that can collect fine saw dust which eventually works on the seal combined with bar oil which acts in a way like valve grinding compound .

One way to check is remove the clutch,fire the saw up and give it just a tiny shot of starting fluid around the shaft .Just a tiny little poof not a big squirt else you could cook the cylinder .Might not be a bad idea just to change it  seals aren't that expensive

[shadycon]

Thank you for your suggestions. I will try/check items mentioned.

[joe_indi]

Al's suggestion on seals got me thinking of yet another possibility.
Stihl has a different type of oil seal (easy fit) for most of their clam shells (short blocks).
These oil seals do not require the engine pan to be loosened for seal replacement. You use an oil seal puller to get the old seals out and just press in the easy fit seals.
These seals need to be installed inside out. The shape of the inner part is different as well as the outer edge, which is tapered.
If by chance the easy fit seals are installed normally (inside in not inside out), chances are they would leak, when warm, hot or at random.
These seals have the inner portion colored a dark brown instead of the usual deep blue

[shadycon]

Well the temp got up to 50* today so I took the saw apart. The impulse line and intake boot are still good. Cleaned all the old grease/oil /sawdust and dirt out and put it back together. Seals were replaced 2 yrs. ago. Could not find anything wrong. Started it up and very carefully readjusted the carb., It idles and has good throttle response. I'll see what happens next time I use it. ;)

[shadycon]

I tried it out yesterday; Results are, runs better, has a little surging at low speed, not over reving like it was, But still won't start when hot. I'll play with carb. adj. a little more. My guess it's getting old like me!