I fixed it, sort of.... carb question?

[kayaklogger]

In a fit of frustration I tore into both of the used 066's I recently bought, both advertized as low hours saws, both were clearly not. Seeing as how I've always viewed the internal combustion engine as a magic box that only people that grew up as rednecks understand, I'm pretty proud of myself for figuring out not one, but both dead saws. One had a loose spark plug that killed the compression, the other had some misaligned parts in the handle trigger assembly. So, got them both running but there is a big difference, the older one runs at what I think are normal carb settings, one full turn to the left on both screws and then a little tweaking. The other saw, however, only ran if I richened the low speed screw about two turns to the left and then turned the idle all the way up. Anyone know what's going on here? Maybe I don't quite understand where those screws should be set? can someone help me? The stihl manual says to start 1/4 turn from max lean, (thats all the way to the right and then back 1/4 turn right?)

I'm at sea level, can someone get me in the ball park on the screws so I can at least get it to pop again, I lost the adjustment I made this afternoon and now it won't fire at all. Got spark.

 

[wigglesworth]

In a fit of frustration I tore into both of the used 066's I recently bought, both advertized as low hours saws, both were clearly not. Seeing as how I've always viewed the internal combustion engine as a magic box that only people that grew up as rednecks understand,

As one who grew up a redneck, I dont know if I should be offended or proud. LOL

The other saw, however, only ran if I richened the low speed screw about two turns to the left and then turned the idle all the way up. Anyone know what's going on here?

You my friend hava an air leak. Do not run the saw until it is fixed. You will toast it, if you already havent. Check the simple things first, intake boot could be torn, impulse line could be torn, fuel line torn, carb loose, cylinder bolts loose etc. etc, and if that doesnt get ya, it could be time for crank seals. But if it wont run now, take the muffler off and have a look in that cylinder for damage.

 

[Brmorgan]

Glad you made some progress. It's satisfying to figure out a problem on your own and realize things aren't as bad as once thought, eh?

Two turns out on the Low and all the way in on the idle are really good signs of an air leak somewhere, and most likely your impulse line or intake-to-carb gasket, since it's more prevalent at low RPMs - those would cause a racing idle followed by a stall or almost stall, and a very difficult throttle response. You're having to richen up the mixture coming from the carb in order to offset the extra raw air being drawn into the case from elsewhere. I was running into this issue with the 031AV I just built, turned out the impulse line had a significant hole; I was surprised it would run at all like that.

If your idle is all over the place and the saw leans out noticeably at WOT, you may have a hole in the main fuel line, which allows air to get into all parts of the carb and can lean out the mixture throughout the throttle range, and is a really good way to demolish a piston if held at high RPM.

Check all of these first, if none fix the problem it could be the crank bearings / seals, or the cylinder base gasket. Only way to test the crank is with some vacuum / pressure testing equipment.

 

[LAndrews]

Could also be gunk in the carb passages. Always worth the half-hour to download the carb manual and rebuild it carefully. Carb's gotta come out to check the manifold anyway...and that's at least as likely as the carby.

hth, la

 

[BobL]

I agree with the others, it sounds like you have an air leak - investigate that before you do anything else.

The stihl manual says to start 1/4 turn from max lean, (thats all the way to the right and then back 1/4 turn right?) I'm at sea level, can someone get me in the ball park on the screws so I can at least get it to pop again, I lost the adjustment I made this afternoon and now it won't fire at all. Got spark.

My 660 manual says

If the carburetor has to be adjusted from scratch, carefully screw both adjusting screws clock-
wise down onto their seats to obtain a starting point for fine tuning.
Then make the following adjustments:
High speed adjusting screw H: back off 1 full turn
Low speed adjusting screw L: back off 1 full turn

The saw must be run with the basic carburetor setting (H = 1, L = 1) if an accurate tachometer is not available for checking the engine's maximum speed.