HELP! MS 660 carb issue

[whybother]

I'll try to get some video when I get back to it this week.

 

[drf256]

There is a low base and a high base cyl for the 066/660. I cannot remember the particular applications but I wonder if they could be mistakenly switched, and still run somewhat?

I’m not sure on this. Do you mean thick vs thin base? The only thin base jugs I know of were 52mm 064. The 52mm 650 and all 54mm 066/660 jugs I’ve seen are thick.

 

[whybother]

There is a low base and a high base cyl for the 066/660. I cannot remember the particular applications but I wonder if they could be mistakenly switched, and still run somewhat?

I’m not sure on this. Do you mean thick vs thin base? The only thin base jugs I know of were 52mm 064. The 52mm 650 and all 54mm 066/660 jugs I’ve seen are thick.

I had a minute to look at this and with the jug bolted down getting a good base measurement is not easy...
However measured it every way could think of and tried to do the same with the trashed jug on a flat surface. They are identical as far as I can tell.

 

[whybother]

So I finally got to mess with this again. New intake boot made no change. Swapped to stock muffler, no change. Swapped coil, now the high jet can be turned out about 1/2 a turn. Still not right IMO. This one has a poly flywheel if that makes any difference.

 

[drf256]

I know it sounds absurd, but did you change the plug? What about the lead wire from the coil?

We are now at the “it’s gonna be something dumb” stage. The fact that a coil changed it means something.

I spent $100’s on a Honda engine that was the $2 spark plug. Plug only failed when the engine got hot. Now it’s my first move.

Had an 036 that would run OK and then stop. Was a tiny crack at the neck of the oem fuel filter. Could barely see it. I found it after I threw my hands in the air and split the case, redid it all.

 

[Wonkydonkey]

I'm Looking at your jug & slug pics, ?

you cleaned the slug ?

Is that a bit of detonation I see on the front pto side .?

 

[drf256]

Do you have another flywheel to swap in? I have heard of the ring on the poly flywheels slipping and throwing off the timing. See if you could pop one off another saw and try it. Many of us should have one lying around if you need one.

 

[stihl #1]

Just saw this thread. If the H screw is not adjusting and you can close it and the saw runs at wide open throttle, then the carb is leaking fuel internally making the saw run rich. Too much fuel. An air leak in the crankcase, or low impulse signal. or restricted fuel delivery will cause lean running, not rich.


Try tuning with the air filter off and see if it makes a difference. I have had that happen where a pleated filter looks clean but it in fact restricted. If the big welch plug is leaking that can cause this but it usually causes rich running at idle. Older carbs had a sealant around the welch plug and ethanol fuel will dissolve it. As someone posted earlier, if the main nozzle check valve is leaking this won't cause rich WOT but just messes up the idle. To test the metering chamber for leaks at either check valve and the welch plug a vacuum must be pulled on the metering chamber with some special tools. I can post more about that if you need me to.

 

[whybother]

I know it sounds absurd, but did you change the plug? Yes, sapped it with a new E3. What about the lead wire from the coil? Yes, swapped a complete known good coil, lead and boot in.

We are now at the “it’s gonna be something dumb” stage. The fact that a coil changed it means something. Agreed, it's something simple.

I'm Looking at your jug & slug pics, ?

you cleaned the slug ? I wiped the oil of the skirt for better pics, I did nothing to the top of the piston. It's brand new oem with less than an hour run time on it.

Is that a bit of detonation I see on the front pto side .? I did not see anything suspicious al though it does kind of look like it in the pic. Probably caused my ny potato phone.

Do you have another flywheel to swap in? I have heard of the ring on the poly flywheels slipping and throwing off the timing. See if you could pop one off another saw and try it. Many of us should have one lying around if you need one. No I don't have a spare flywheel. If someone has they one they would get rid of message me please. Will the poly and aluminum flywheels interchange? I'd prefer an aluminum one, not a fan of plastic in this application.

Just saw this thread. If the H screw is not adjusting and you can close it and the saw runs at wide open throttle, then the carb is leaking fuel internally making the saw run rich. Too much fuel. An air leak in the crankcase, or low impulse signal. or restricted fuel delivery will cause lean running, not rich. Yes it's running rich. I swapped in a brand new carb and it didn't change anything.


Try tuning with the air filter off and see if it makes a difference. I have had that happen where a pleated filter looks clean but it in fact restricted. If the big welch plug is leaking that can cause this but it usually causes rich running at idle. Older carbs had a sealant around the welch plug and ethanol fuel will dissolve it. As someone posted earlier, if the main nozzle check valve is leaking this won't cause rich WOT but just messes up the idle. To test the metering chamber for leaks at either check valve and the welch plug a vacuum must be pulled on the metering chamber with some special tools. I can post more about that if you need me to. I will try tuning with the filter off. It is running a Max Flow filter system and I cleaned and re-oiled it before starting this little adventure. Please post up about how to vac test the metering chamber. That info might come in useful.

Responses in red. Thank you everyone!

 

[Dolkitafreak]

Responses in red. Thank you everyone!

E3 are hot garbage, try another plug even if not the solution…doing yourself a huge favor!

 

[EFSM]

E3 are hot garbage, try another plug even if not the solution…doing yourself a huge favor!

Amen!

 

[whybother]

E3 are hot garbage, try another plug even if not the solution…doing yourself a huge favor!

Amen!

Any plug recommendations? As long as it's not NGK I'll try it.

 

[Dolkitafreak]

Any plug recommendations? As long as it's not NGK I'll try it.

NGK makes quality plugs, beware counterfeit are a thing now…thanks chyna.

I like NGK, Bosch, and Autolite, champion work.

 

[stihl #1]

I checked it with a straight edge, it looked correct. I'll double check it with the proper tool.


Cleaned it and put a kit in it while i had the saw apart. Didn't see anything unusually dirty or plugged up. I'll pull it apart and double check it.

Trying to think of a situation that would only cause rich running at WOT, and I just can't recall ever being there with a carb fault. Other than a clogged air filter. You mentioned the metering lever. On a WJ it is not flush with the gasket surface but is slightly lower. The walbro gauge on the left has a tab, in the middle, that is used to check it.

If the lever is too high then the carb will flood as soon as you put the cover and dia on. I suppose it could be higher than it should but not high enough to flood, and possibly cause what you are seeing. Also be sure the gasket is on the carb body and the dia next to the cover.

 

[Fleethirte]

this may be silly suggestion, but is your throttle linkage bent and preventing max RPM?

i had to replace one once

 

[whybother]

Trying to think of a situation that would only cause rich running at WOT, and I just can't recall ever being there with a carb fault. Other than a clogged air filter. You mentioned the metering lever. On a WJ it is not flush with the gasket surface but is slightly lower. The walbro gauge on the left has a tab, in the middle, that is used to check it.View attachment 426422
View attachment 426423
If the lever is too high then the carb will flood as soon as you put the cover and dia on. I suppose it could be higher than it should but not high enough to flood, and possibly cause what you are seeing. Also be sure the gasket is on the carb body and the dia next to the cover.

I have the Walbro and Zama gauges and even used when I tore the apart the second time. It was spot on no adjustment needed. Yes gasket and Dia are in correct location.

 

[whybother]

this may be silly suggestion, but is your throttle linkage bent and preventing max RPM?

i had to replace one once

You know, I hook up the linkage and hit it to make sure it's working. I've never had a reason to question it being bent before.
This one was apart when it was dropped off. Whoever took it apart could have easily bent it if they got rough with it. I'll definitely check it out.