2008 Stihl 880 Runs like a dog

[Derrick Sawyer]

Hey Ya'll,
Buddy told me his stihl 880 was running weak. I checked it out, its a 2008 model, compression 150psi, piston looks fine, carb had some residue so I sonicated and rebuilt in same fashion as I always do with success, the carb is Tillotson HT10A, had a removable jet and also another bronze looking port that doesn't unscrew, shaped almost like the top of a round chimney, the hole is big, not a pinhole. I trimmed the limiter as well.

Vacuum and pressured tested fine.

Can't seem to get this cutting, was able to a little over 12K rpm before the coil cut in and messed up the tach reading. The setting for this was the high carb screw was only 1/2 out, which is the setting with the limiter, but usually is 1 turn out without limiter.

Made some cuts, was better, but still bogs with no pressure with 42" bar, and then dies. I can restart fine but still low power. I am hesitant to turn screw in more since I don't want to run lean, though at 1/2 out, plug is still tan colored.

Is that extra carb valve putting in extra gas mix?

I did expand the muffler port as much as I could within the deflector.

Frustrating since its a pain with such a big saw .

Any help? I read a lot of previous posts but i'm still confused

 

[Brian Carlson]

Might try new fuel lines. The line may be sucking in while your running and cutting fuel off or maybe the filter is stopped up.

 

[Derrick Sawyer]

Thanks for the reply, I did pressure check the fuel line, cleaned the air filter and tank vent, fuel filter is fine, and it starts, runs and revs great.

 

[Brian Carlson]

Might try a different carb and see if that helps. Just my gut telling me it's in the fuel system.

 

[kwhite87]

Is the saw four stroking at all when you are testing it? Before the cut, in the cut? For me bogging leads me to believe it's running rich. Is it being any smoke? I would lean it out a little to see if the performance improves

 

[Derrick Sawyer]

Yeah I'll see if i can swap a different carb in. Seemed to be 4-stroking when i leaned it out to just when the coil started to limit the revs. Does it need to be leaned out a fraction beyond that and then tested it in the cut, making sure it cleans up when cutting?

 

[67L36Driver]

The Stihl tec tells me it's 10,500 with a Tilly and 11,000 with the Walbro (or vice versa).

Personally I'd set it for 10,000 at most,

The 880 is not a high speed piss rev'er. Long stroke and heavy piston.

 

[Four Paws]

Tune it in the wood for maximum performance.

If it was running strong, but is no longer running strong (step change in performance) and has good compression but bogs/stalls in the cut, look at the intake tract for an air leak.

I know that you said it pressure/vacuum tests fine. My theory is you perform that test cold. When the saw is hot and crankcase vacuum under load is drawing in fresh charge, your saw is also managing to suck in some air from a leam, causing it to go lean and run out of power. I have seen it happen...saw had a normal idle and restarted great.

Good luck

 

[lone wolf]

Tune it in the wood for maximum performance.

If it was running strong, but is no longer running strong (step change in performance) and has good compression but bogs/stalls in the cut, look at the intake tract for an air leak.

I know that you said it pressure/vacuum tests fine. My theory is you perform that test cold. When the saw is hot and crankcase vacuum under load is drawing in fresh charge, your saw is also managing to suck in some air from a leam, causing it to go lean and run out of power. I have seen it happen...saw had a normal idle and restarted great.

Good luck

Or did he mean he pressure checked the fuel line not the engine?