026 races then dies

[rsk]

My stihl 026 has started playing up: the saw races when the throttle is off, and when the throttle is applied the revs dip and it dies. It's an old saw, but was repaired and tuned fairly recently so I'm pretty sure it's not a tuning issue.

Any ideas???

[agg221]

Sounds like it's running very lean, then when you pull the trigger it's so lean it won't even run. Those are symptoms of an air leak.

 

If it's recently repaired, I'd be looking at whether the carb boot was refitted properly and sealed at each end. I would then look over the boot thoroughly for cracks and splits. The other source of leaks is the crank case, through the gasket or the bearing seals, but testing that is trickier and unless you want to make a habit of it, I'd get someone else to.

 

Mine go to Spudulike on here for thorough diagnosis and testing - very thorough and makes a point of looking for things that are likely to go wrong in the future. Whereabouts are you?

 

Alec

[rsk]

Thanks for reply, I'm in Sheffield

[agg221]

Hmmm, Spudulike is in Baldock - not the closest. Afraid I don't know anyone up your way.

 

Alec

[spudulike]

Blimey Alec - you have been listening to me - spot on diagnosis - crank seals, impulse line or carb boot - running it this way may cause some damage to the cylinder and piston.

 

It is possible the fuel line is holed or the carb has some crap in it or a breather is blocked but I would start with a pressure check and go from there.

 

If you get stuck then parcels2go can get a saw to me for £6.50 which is a decent price - am not around next week but pick the spanners up again the week after:thumbup:

[agg221]

Blimey Alec - you have been listening to me

 

I know I may have a vacant look, but it's going in honestly I thought you'd gone already, otherwise I'd have left this to the master!

 

I reckon my money is on the carb boot. This is due to the combination of it being an older saw so more likely to be cracked or perished, having been worked on recently so more likely to have been disturbed and because it sounds like it came on suddenly and was immediately very extreme - suggests it didn't fail gradually while the engine was running which I would have expected of a bearing seal or crankcase seal. If it had come on gradually I would have expected it to have either been picked up as a climbing engine note, or not noticed resulting in seizure. For the same reasons, second choice from Spudulike's list would be blockage in the carb.

 

Be interesting to see if I'm right.

 

Alec

[spudulike]

The racing idle is a classic air leak symptom - and is usually a sign of a bad one and a split carb boot is high up on the usual suspects, more so than a crankshaft seal. Possible split impulse line, this can stop so much fuel getting in to the carb and cause similar problems but you are probably right.

 

If the saw makes a whoom whoom noise in the mid range and dies on mid to high revs then this is also typical - bit like a 3 series Husky before it has warmed for 15 seconds!

 

Hope the oiler on the 066 is now good - it was throwing it out when I ran it up and all fom the right place:thumbup: