Stihl MS192 TC Bogs/Stalls when Cold

[BSS]

Alright, attempted to retune the saw again yesterday and had some interesting results. I'm not really sure what to make of this, because following the manual's instructions had the saw bogging every time I pressed the throttle. Only after noodling with the L jet by little increments was I able to get the saw to rev. After that I adjusted the H jet and was able to hit ~13,500 RPM, with decent responsiveness. After that, the saw actually seemed surprisingly normal! I can't help but feel like it's still slightly under-powered, but again, I might just be subconsciously comparing it to my 372XP, which is about 4x as much horsepower. I've attached a little test-cut video I uploaded, sorry about the bad framing - I'm not very good at this. The close-up was supposed to show the tach numbers, which were hitting 13,300-13,600 highs and ~3k on lows. Seems to be pretty stable, but the jury is still out until next time I start it cold Does anyone think this seems bad/slow for a cut this size?



After I ran the saw for about 5-10 minutes, I could see more smoke occasionally on the muffler. Looking more closely at the saw, I noticed pooling oil on the bar cover, just above the muffler. Anyone have any idea why it would be kicking oil back here? I feel like something is amiss, but I'm not really sure where to start trouble-shooting this one. See picture near where my finger is pointing. Earlier on, there was a bit of a pool forming around that area, and near the top holes of the mesh:

 

[cookies]

It sounds too lean on the H needle, try aiming for 13k or 12800 rpm so that it slightly fuel bogs until you start cutting with it. Sharpen the chain, they make little dogs for them. They seem to really shine with a 12" bar

 

[BSS]

It sounds too lean on the H needle, try aiming for 13k or 12800 rpm so that it slightly fuel bogs until you start cutting with it. Sharpen the chain, they make little dogs for them. They seem to really shine with a 12" bar

Haha, this was after I did a 3-4 stroke pass with a file. I guess I can try again, not sure if I really got it sharp enough, maybe it needs a few more passes. As for the RPMs, that's interesting, the Technical overview said "permissible max speed with bar and chain: 13,500 RPM" so I figured that was the goal. But now that I read it, it does make it sound like you never want to go beyond that.
I just did a quick cold test-run again 5 minutes ago and it started fine, but bogged as soon as I pressed the throttle - @$&%! I don't know what the hell is going on with this thing now. After I feathered it up to high RPMs 2-3 times, it seemed to run ok, so that at least is an improvement over past attempts. However, I was watching the tach again and it started cold at 2,800 RPM. After revving a few times, it was idling at 3,400, slowly dropping back to 3,100 after about 20 seconds. Tilting angles had no effect on RPMs, but still seemed odd I'd have this much variance. I did a couple more dry revs and it went up to 13,800 and touched 14,000! But then the next rev it was back to 13,500 - What the hell? I'm not really sure what else to check on this thing, unless the replacement carb I got is also a dud somehow! Gah, this is getting old. . .

 

[mountainlake]

Your chain is REALLY dull. Steve

 

[cookies]

+ or - 200 rpm is normal, adjust the carb as I suggested and see if it calms down some, if not you may have a dud. If your chains chisels are sharp then your rakers are too high.

 

[BSS]

+ or - 200 rpm is normal, adjust the carb as I suggested and see if it calms down some, if not you may have a dud. If your chains chisels are sharp then your rakers are too high.

Thanks for the reply, I'll give it a shot! I'll hit the rakers a few times as well and see if that helps!

 

[lone wolf]

Can you do a compression test on that saw?

 

[BSS]

Can you do a compression test on that saw?

I don't currently have a compression tester, but if you guys think that's the next thing to check, I guess I'll have to decide if I want to throw more money at this learning experience, haha. Thing is, the rings looked great (as far as I could tell, anyway). Is there anything else that could be causing bad compression?

Carb (or something else) is still giving me bog issues when it's cold, can't seem to get it to rev at all if I fully depress the throttle. . .
I've been looking over the service manual again, and assuming the carb isn't to blame, it seems like the remaining things to check are:
1. Fuel filter clogging - seems unlikely since I've replaced it, though the replacement wasn't 'new' but didn't look bad. Could try replacing again.
2. Clogged tank vent - also seems unlikely since I replaced that as well, but could try to clean it again.
3. Dirty air filter - could try taking it off when running just to see if it makes any difference.
4. Leaking fuel line to carb - unlikely as I've replaced & done a poor man's pressure test on it and it seemed fine, but could try swapping with original again.
Anything else I've missed? Impulse line is new and everything else seems carb-related. Weird thing about this issue is once I feather the throttle a few times, it is fine and revs more or less normally. This makes me think it is a carb problem, but it just seems so odd. I guess I could just have two bad carbs, but given they both exhibit the exact same behavior, I suspect there's something wrong with the saw that I'm missing. . .

 

[cookies]

Low compression also means low vacuum, compression testing is a key tool in providing valuable information.
Saw carbs drain back into the fuel tank, it can take 5-7 seconds or even a little longer to get all the air out of the fuel line and carb. If compression/vacuum is weak it will make that time even longer.

 

[BSS]

Didn't mean to kill this thread, but I ended up going on a family trip and lost some steam on this project. Finally picked it up again last week with my dad (who is an old car mechanic) and he helped me do a backwoods poor man's compression test (with the finger over the hole). We compared the compression on the Stihl to my other saw (Husqvarna 372xp). While the xp is obviously a much beefier saw, the difference was night and day. The xp blew our fingers off the hole while the Stihl barely pushed it at all. I don't have any actual numbers here, but it defintely seems like poor compression is a likely candidate for my issues. That kind of sucks because that would mean sinking another ~$50 or so on a new engine assembly, and I'm not really sure it's worth it for me to throw more money at this thing anymore. Lesson learned, $20 garage sale saws are full of surprises. At least it was a great learning experience. . .