084 Av Stihl Nightmare

[Max Gilbert]

Hello All!
I have been lurking on this site for over a year now and have never had a problem that was not already addressed elsewhere, but I do now!
I have a Stihl 084 that I'm working on for a customer that has me completely stumped. It is currently firing and running a few seconds and quitting but won't stay running. I have to this point replaced a semi firing coil with a 066 coil, changed the flywheel slot to b as well. (Thanks to the thread about that) Image cleaned the carb twice with an ultrasonic and rebuilt I have set the metering lever flush with the bottom of the carb it's a tillotson ht7a. The impulse line is good as well as the fuel lines. The saw has every indication of running very rich, white thick smoke, wet plug, and a muffler full of condensed gas and vapor after pulling a few times. I have checked the metering lever many times and adjusted the mixture screws to one turn out each and still no luck. I have fiddled with the mixture screws to no avail. The cylinder and piston is good and clean and I'm completely stumped and well over 12 hours in. Any ideas? I promise infinite good karma and an imaginary case of your favorite adult beverage for anyone who can help solve this nightmare.

 

[Brandon Bondeson]

Does it seem to bog out before it dies?


Sent from my iPad using Tapatalk

 

[Brandon Bondeson]

Had the same problem with a 272xp turned out the oil pump quit making the bar&chain overheat and seize which resulted in the saw bogging out and quitting after a few minutes of running


Sent from my iPad using Tapatalk

 

[Max Gilbert]

This one won't idle for more than a few seconds before dying. It will rev up a little blowing plenty of smoke and then quitting. it's wet fouling the plug. Although I can't be sure if that's the whole problem. I'm getting a lot of mixed signals from this saw. These tillotson carbs give me problems every time Stihl saws especially. I just don't work on enough of them I suppose. I can't find any service info on the ht series either.

 

[67L36Driver]

Gasket and diaphragm in correct order on metering side of carb?

Gasket first against carb body.

 

[pioneerguy600]

Any idea of the compression on the saw and if the mufflers screen is still in or not, clean and open or stuffed up with carbon?

 

[pioneerguy600]

This one won't idle for more than a few seconds before dying. It will rev up a little blowing plenty of smoke and then quitting. it's wet fouling the plug. Although I can't be sure if that's the whole problem. I'm getting a lot of mixed signals from this saw. These tillotson carbs give me problems every time Stihl saws especially. I just don't work on enough of them I suppose. I can't find any service info on the ht series either.

The ht carb does have a problematic part in it but I will wait til I hear back from my post above. I don`t like jumping to conclusions.

 

[Max Gilbert]

Yes I double checked the gasket diaphragm order just to make sure. I removed the spark screen so it wouldn't be a factor. The compression gauge reads 92 psi.

 

[pioneerguy600]

If 92 psi is the correct compression reading then that is really low. Is the rings free moving in the piston lands.?

 

[Max Gilbert]

What is the proper way to check the compression on this saw? I screwed in the gauge and pulled it three times with the decompression button pulled up. (Sealed) It was difficult to pull, could I be pulling it too slowly or is this one dead in the water?

 

[Brandon Bondeson]

Wow I didn't think a saw would even start with 92psi compression


Sent from my iPad using Tapatalk

 

[pioneerguy600]

To get a true compression reading one must keep pulling the saw over until the comp gauge stops increasing, even 20 or more pulls on some saws.

 

[Max Gilbert]

Good to know. I usually dont use a comp gauge on a saw. I pulled it 10 or so times more and the gauge stopped at 120 for the last 4 or so pulls.

 

[Brandon Bondeson]

120 is still extremely low I would say you to get new rings at least if not a full rebuild would be necessary but 120psi just won't cut it for a chainsaw


Sent from my iPad using Tapatalk

 

[Max Gilbert]

Thanks for the help. I managed to get it to 140 after more pulling and cussing. So, new rings it is then. I'll call my local Stihl dealer in the morning and order them.

 

[pioneerguy600]

Thanks for the help. I managed to get it to 140 after more pulling and cussing. So, new rings it is then. I'll call my local Stihl dealer in the morning and order them.

Some more compression certainly would help. Did you just get it up to 140 lbs? If it made 140 it will run fairly well.

There is a check nozzle in the Tillotson HT-7A carbs, when it fails it will flood out the saw and it will need replacing or they can be removed and soldered shut, put back in. What they do, when working correctly, is to act as a governor to prevent over rev in big saw engines. They activate from vibrations, when an engine reaches a pre determined RPM it makes the correct vibrations to cause the ,check valve to open and add fuel,enriching the mix enough to slow the engine. Tillotson part number, 363-600.

 

[Ikeholt]

Order a new carb while you're at. 140 Compression isn't that bad to cause it to stall, especially with that long hose you have on the gauge. Compression check a good running saw around there and see what it reads. If it wasn't frustrating, it would get boring.

 

[Max Gilbert]

Yes it got up to 140. I've got the carb apart where is the check valve. I'm looking at the metering side there is a removable jet that says .90mm is that it?

 

[pioneerguy600]

Look in the carb bore or venturi, should be a round brass looking tube just sticking up out of the carb wall, they press out and in, no threads.

 

[a. palmer jr.]

I had a similar problem on my 038 and replacing that old troublesome Tillotson carb did the trick. If the saw has 140 compression it should run, of course more is better.