Stihl 024 AVS with strange symptoms

[ktpnw]

Hello chainsaw experts. I have a Stihl 024 AVS which is exhibiting strange and counterintuitive symptoms (by my understanding anyways). It has fresh crank seals and a freshly rebuilt OEM carb, which is set at factory settings.

The weird symptoms are:

- muffler gets HOT. Not red hot, but hot enough I can’t hold the handle without a glove on and it’s melting the top plastic. I know high heat indicates running lean.
- however at the same time the spark plug is black and sooty, and it smokes on throttle, which to me indicates rich condition.
- also it idles slightly higher when tipped on either side, which is why I replaced crank seals, but that did not improve anything.

Any ideas? I know two of these symptoms would be indicative of an air leak, but the third (sooty spark plug and smoke) seems to indicate the opposite. I’ve tried adjusting the carb a quarter turn or so from factory settings also, and wasn’t able to make any progress. Thanks in advance for any insights.

 

[L34]

Is the muffler blocked/full of carbon that is burning?

 

[ktpnw]

Not blocked, I did take it off and make sure the screen was clear/etc but could be full of carbon. I will give it a clean and see if that helps. I don’t see how that would explain the changing idle when tipped and sooty spark plug though?

 

[Bob Hedgecutter]

Did you pressure test AFTER installing the new seals?
You would not be the first person on Earth that had a mishap seating small oil seals and although new- they leak.
Did you pressure test to delete blame from any other possible leak points?
Are you 100% it has an 024 muffler on it and not something physically larger?

Then finally- when you removed the flywheel to do the seals- how did the key and keyway look? Were they aligned perfectly and holding nut torqued down well?
Firing at the incorrect timing can do wonders for the heat being created.

 

[SteveSr]

Hello chainsaw experts. I have a Stihl 024 AVS which is exhibiting strange and counterintuitive symptoms (by my understanding anyways). It has fresh crank seals and a freshly rebuilt OEM carb, which is set at factory settings.

The weird symptoms are:

- muffler gets HOT. Not red hot, but hot enough I can’t hold the handle without a glove on and it’s melting the top plastic. I know high heat indicates running lean.
- however at the same time the spark plug is black and sooty, and it smokes on throttle, which to me indicates rich condition.
- also it idles slightly higher when tipped on either side, which is why I replaced crank seals, but that did not improve anything.

Any ideas? I know two of these symptoms would be indicative of an air leak, but the third (sooty spark plug and smoke) seems to indicate the opposite. I’ve tried adjusting the carb a quarter turn or so from factory settings also, and wasn’t able to make any progress. Thanks in advance for any insights.

You likely have an ignition timing issue. I believe that retarded timing will increase the heat in the cylinder. I think that they used to do this on purpose in car engines to get them to warm up faster.

Check the FW and key. If these are correct the last possibilities are the ignition module or the wrong FW.

 

[ktpnw]

Excellent, thanks to everyone. I pulled the flywheel obviously to change the seals and everything looked normal (key was in place, everything came apart and went together smoothly) but I didn't give it a super close inspection, which I will do. It is an OEM Stihl flywheel so I will check the part number to make sure its correct.

I did not pressure test after installing the seals, that is a good call as well. Although again, it seems that an air leak would cause the opposite of smoky/sootiness. But I could have more than one issue of course.

To clarify on the smoke - there is both a large puff of smoke when I hit the throttle, and a general smoke emanating from the front of the saw after it warms up. The latter I think could be explained by carbon buildup in the muffler, which I will clean out and/or an overheating cylinder due to messed up timing as explained above. But the former seems to me to indicate rich condition, no?

 

[Mad Professor]

First are you sure you didn't make a mistake and put too much oil in the mix?

Are the gaskets in the carb installed in proper order? And some kits contain gaskets for several similar carbs, they need to be the right ones.

I take each side of carb apart separately, and lay things out in the order and orientation they come off. When all is clean I match the gaskets with those in the carb kit

Did you change the metering needle in the carb, was the seat clean, and metering lever set?

 

[Bob Hedgecutter]

With the muffler off for cleaning- look in the exhaust port, the port itself and the face/top of the piston.
Are these also full of sooty carbon?
Could be- a weird and wonderful choice and mix ratio of oil has lead to a high carbon build up and it is causing your heat issues as it glows a nice red hot glow under running conditions.

 

[Bob Hedgecutter]

Excellent, thanks to everyone. I pulled the flywheel obviously to change the seals and everything looked normal (key was in place, everything came apart and went together smoothly) but I didn't give it a super close inspection, which I will do. It is an OEM Stihl flywheel so I will check the part number to make sure its correct.

I did not pressure test after installing the seals, that is a good call as well. Although again, it seems that an air leak would cause the opposite of smoky/sootiness. But I could have more than one issue of course.

To clarify on the smoke - there is both a large puff of smoke when I hit the throttle, and a general smoke emanating from the front of the saw after it warms up. The latter I think could be explained by carbon buildup in the muffler, which I will clean out and/or an overheating cylinder due to messed up timing as explained above. But the former seems to me to indicate rich condition, no?

You may well be rich- but you can also have bad timing and be rich.
As you say, you may have more than one issue. Hopefully we can work through them.
Photographs added of what you are looking at will be helpful- video of the saw running maybe?

 

[ktpnw]

First are you sure you didn't make a mistake and put too much oil in the mix?

Are the gaskets in the carb installed in proper order? And some kits contain gaskets for several similar carbs, they need to be the right ones.

I take each side of carb apart separately, and lay things out in the order and orientation they come off. When all is clean I match the gaskets with those in the carb kit

Did you change the metering needle in the carb, was the seat clean, and metering lever set?

Thanks for the reply. On the oil yes, it's Stihl oil mixed with non ethanol premium at the recommended ratio and it came from the same gas can I use in all my other two stroke machines (which all work great).

On carb gaskets yes, I matched them up to the ones I took out. I suppose it's not impossible that the ones I took out were also wrong (?) but all the holes and such seem to match up correctly.

I pulled and inspected the metering needle and seat. I did not change/check the lever height however, as I could not find the proper spec. This saw is (I believe) an early 024 AVS with a Marvel Schebler Tillotson carb, I could only find specs for the Walbro. So I left that alone. If anyone knows the correct metering lever height I can certainly check that.

Thanks again

 

[ktpnw]

With the muffler off for cleaning- look in the exhaust port, the port itself and the face/top of the piston.
Are these also full of sooty carbon?
Could be- a weird and wonderful choice and mix ratio of oil has lead to a high carbon build up and it is causing your heat issues as it glows a nice red hot glow under running conditions.

The exhaust port (between piston and muffler) is certainly also very sooty. I did not check the top of the piston, I will do that.

 

[ktpnw]

You may well be rich- but you can also have bad timing and be rich.
As you say, you may have more than one issue. Hopefully we can work through them.
Photographs added of what you are looking at will be helpful- video of the saw running maybe?

Thanks. I will try to get some photos/video whenever I have time to get back to the shop.

 

[SteveSr]

Thanks. I will try to get some photos/video whenever I have time to get back to the shop.

I don't recall if some of the 024s came with a points ignition or if they were all electronic. If there were some of both it could be possible that you have a mismatched FW from the other ignition type.

BTW, did this saw run before you started messing with it?

 

[ktpnw]

Hmm. I am 99% sure it has electronic ignition (the ignition module looks like all the other ignition modules I've seen, and it says "electronic quickstop" on the top panel). But I suppose if there was a points version I could have the wrong flywheel. I'll confirm.

I got this saw for $25 at a garage sale non running, and all I had to do to get it to run was blow out the impulse line. At that point it ran, but not well. (I did also replace the fuel lines and impulse line with new OEM parts btw). Rebuilding and adjusting the carb made it run better, although it still idled high when tipped on either side, thus the crank seal replacement. I would say everything I've done has made it run better, just not all the way there yet.

 

[Bob Hedgecutter]

Hmm. I am 99% sure it has electronic ignition (the ignition module looks like all the other ignition modules I've seen, and it says "electronic quickstop" on the top panel). But I suppose if there was a points version I could have the wrong flywheel. I'll confirm.

I got this saw for $25 at a garage sale non running, and all I had to do to get it to run was blow out the impulse line. At that point it ran, but not well. (I did also replace the fuel lines and impulse line with new OEM parts btw). Rebuilding and adjusting the carb made it run better, although it still idled high when tipped on either side, thus the crank seal replacement. I would say everything I've done has made it run better, just not all the way there yet.

If it says electronic or electronic quick stop and the cover is original to the saw- not points ignition.
But, if you work on, have worked on several saws, like older saws, like a bargain you can fix up- you are a perfect candidate for a Mityvac 8500 (or cheaper lesser brand named one) as your next tool purchase- they just save SO much guessing.

 

[ktpnw]

If it says electronic or electronic quick stop and the cover is original to the saw- not points ignition.
But, if you work on, have worked on several saws, like older saws, like a bargain you can fix up- you are a perfect candidate for a Mityvac 8500 (or cheaper lesser brand named one) as your next tool purchase- they just save SO much guessing.

Yep, I have one! Just need to find the time to scrounge the rubber bits and do a pressure test. Hopefully next few days I'll be able to make it happen.

 

[Bob Hedgecutter]

Yep, I have one! Just need to find the time to scrounge the rubber bits and do a pressure test. Hopefully next few days I'll be able to make it happen.

Do you have a tyre shop close by- or better yet a commercial/tractor tyre shop?
One damaged tractor inner tube will last you a lifetime for simple saws like the 024- just use the carb and muffler to clamp the rubber in place- test through the impulse line.
You do not need all the fancy Stihl adapters to do the test.

 

[SteveSr]

Hmm. I am 99% sure it has electronic ignition (the ignition module looks like all the other ignition modules I've seen, and it says "electronic quickstop" on the top panel). But I suppose if there was a points version I could have the wrong flywheel. I'll confirm.

I got this saw for $25 at a garage sale non running, and all I had to do to get it to run was blow out the impulse line. At that point it ran, but not well. (I did also replace the fuel lines and impulse line with new OEM parts btw). Rebuilding and adjusting the carb made it run better, although it still idled high when tipped on either side, thus the crank seal replacement. I would say everything I've done has made it run better, just not all the way there yet.

Check your PMs for some extra reading material.

It looks like the 024 uses the generic 0000-400-1300 ignition coil or at least superseded to. These should be readily available used on Ebay. Avoid Chicom stuff.

BTW, what is the part number on the existing coil?

 

[ktpnw]

So I just did some work. The main things I did were clean the muffler and clean off/ readjust the coil - it appears to have solved the smoke, and excessive heat - hurrah! It’s running decent now. However the racing idle when tipped on its side is still there.

I went to attempt a pressure test (I have plenty of bicycle inner tube) but I couldn’t figure out how to access the impulse line with the carb installed, nor could I find another way to clamp the tube over the inlet port without a fair amount of work making/buying an adapter. The carb has a barb that goes straight into the impulse line, so it is fully covered when the carb is installed. Am I missing something?

Below is a link to a video showing how it is currently running. I’m thinking I had two problems, I solved one, and now I just have to track down an air leak?

 

[ktpnw]

Check your PMs for some extra reading material.

It looks like the 024 uses the generic 0000-400-1300 ignition coil or at least superseded to. These should be readily available used on Ebay. Avoid Chicom stuff.

BTW, what is the part number on the existing coil?

Thanks so much! I’ve got some reading to do. Not sure about the part number on the coil but per my previous post, that part of the problem may be solved.