HELP! MS 660 carb issue

[av8or3]

OK fellas an update. Original carb was soaking until today. put it back together and it does the same thing no rpm until high jet is closed.
I received the new carb I got from av8or3 (Thank you sir!) today also so i thought I'd swap it in and try it. Same exact outcome as the old carb. Pressure/vac double check is next for it. Anyone have any other ideas of what to check?

I’m so sorry to hear that. Could it be missing the “wedding ring” that holds the intake boot open behind the carb? I think the 066 has that. Not sure. Could a gasket have slipped over a transfer? Or into the intake somehow?

 

[cus_deluxe]

sounds like the carb isnt the issue if a brand new oem acts the same. is choke linkage working properly?

 

[av8or3]

You know it’s not related really. But I went down in flames to the Left magneto on a TSIO520 Wednesday afternoon. I could not get that thing timed to the engine to save my life. This is something I have done hundreds of times , maybe even thousand. Takes me 20 min. Usually. I’m into this thing for HOURS. It’s just not working. Quarter after 5:00 I throw in the towel. I got the next day off, I’m done. The next morning I thought of something I hadn’t tried the day before. I jumped in the truck and drove to the airport and my idea worked. I had it going in 21 minutes. The rest of my day off was much better. If there’s a moral to the story here, it’s one I have to remind myself of from time to time, it will get fixed, one way or another, nothing stays broke unless we allow it.
It will get fixed.

 

[whybother]

I really have no idea. Sometimes when things get really strange, it’s best to go back to basics. Inspect everything from the ground up.

I had a buddy who was very precise and clean who left a piece of paper towel in a port once. You put a new oem jug on the saw, so I can’t see it being a piston issue.

There was an issue with the older 661 boots. A rubber washer was stuck in one. Is the intake boot soft enough to be collapsing?

I have seen too big of a muffler mod cause a lack of rpm as well.

Intake boot is supple but not soft if you know what I mean.

I didn't go nuts on the MM, removed the baffle and opened up side port as much as I could retaining the stock deflector. This one does have the stock dual port though. I think I have a stock muffler, I'll swap it and see if that makes a difference. If not she's coming apart.

 

[whybother]

I’m so sorry to hear that. Could it be missing the “wedding ring” that holds the intake boot open behind the carb? I think the 066 has that. Not sure. Could a gasket have slipped over a transfer? Or into the intake somehow?

Wedding ring is there yes. Unless the base gasket moved I don't know how. It looked good and went together easy. Something I learned from my Father and Grandfathers if it doesn't slip together easily something it wrong. Holds true no matter what you are working on. No carb or intake gaskets on it, intake boot does all the work.

sounds like the carb isnt the issue if a brand new oem acts the same. is choke linkage working properly?

Yes sir, That lever drops down and isn't even close to carb lever when choke is off. It snaps out of half choke perfectly also.

You know it’s not related really. But I went down in flames to the Left magneto on a TSIO520 Wednesday afternoon. I could not get that thing timed to the engine to save my life. This is something I have done hundreds of times , maybe even thousand. Takes me 20 min. Usually. I’m into this thing for HOURS. It’s just not working. Quarter after 5:00 I throw in the towel. I got the next day off, I’m done. The next morning I thought of something I hadn’t tried the day before. I jumped in the truck and drove to the airport and my idea worked. I had it going in 21 minutes. The rest of my day off was much better. If there’s a moral to the story here, it’s one I have to remind myself of from time to time, it will get fixed, one way or another, nothing stays broke unless we allow it.
It will get fixed.

Yep, it will get fixed. Some things just take a little longer than others...

 

[Woodwackr]

How do you find using carb cleaner over petrol in the ultrasonic?

Seems to work. I haven't tried gas. My theory is the carb cleaner does a good job of getting any tiny bits of crud as well as dissolving any old gas shellac.

 

[Woodwackr]

I know you swapped the fuel line but check it for any weak spot. I had a new, oe line that was defective with a thin spot that collapsed when throttle was engaged. (070) Saw idled fine...pull the trigger and wouldn't spool up.
I would try another filter as well.

 

[EFSM]

Good that it held pressure. Your nozzle should be good then

Not that this is all that pertinent anymore, but pressure testing the inlet does not test the main jet nozzle check valve, only the pump diaphragm and needle valve. Am I understanding the quote properly?

 

[whybother]

I know you swapped the fuel line but check it for any weak spot. I had a new, oe line that was defective with a thin spot that collapsed when throttle was engaged. (070) Saw idled fine...pull the trigger and wouldn't spool up.
I would try another filter as well.

Yep, all fuel lines and filter are new oem. I have another set of them. I will inspect both and see if I can find anything...

 

[drf256]

He’s getting too much fuel, not too little. A new OEM carb didn’t fix the issue. It doesn’t seem like it’s the fuel system.

A nozzle check valve issue will cause idle problems, not high speed ones. The check valve is there to stop the metering side from pulling air (and not fuel) back in. When the fuel is used, it causes negative pressure to pull the diaphragm up and open the needle. If the main nozzle is wide open, it would pull air instead. At high speed, the nozzle is pulling fuel via Venturi effect and the wet side can only fill itself with fuel via the needle.

So your boot has the inner AND outer surround? You’re 100% right on the fit together easy part.

By the way, did you get an RPM on the saw wide open with the H screwed in?

At this point, I’d pull the jug and boot, inspect everything, possible change boot (even to AM temporarily) and try it. If that doesn’t work, I’d try another coil. If it’s a 660, any “dummy” coil should work.

 

[whybother]

So your boot has the inner AND outer surround? You’re 100% right on the fit together easy part.

Yes both of the metal rings are in place.

By the way, did you get an RPM on the saw wide open with the H screwed in?

11500-12000 service manual says 13500 max. I am aiming for 13000 for break in period.

At this point, I’d pull the jug and boot, inspect everything, possible change boot (even to AM temporarily) and try it. If that doesn’t work, I’d try another coil. If it’s a 660, any “dummy” coil should work.

I'm going to pull it apart. I do have an AM boot, it felt the same as the stock one so stock was reused. It won't hurt to try the AM one.
I can swipe a coil off something if needed for testing.

Thank you to everyone that's chimed in. This one is really testing my patience...

 

[av8or3]

This too, shall pass……

 

[whybother]

So I pulled it apart, I don't see anything out of the ordinary... A couple marks on the intake side of the piston I can't feel them but I see them. I changed the intake boot to the new AM one. I slid it back together using motoseal instead of a base gasket (squish was .050 so plenty of room).
Now I wait until tomorrow afternoon and see what happens...

 

[bigbadbob]

Just for the giggles check your impulse port/hose as well.
seen some weird stuff with blocked one and cracked one

 

[whybother]

Just for the giggles check your impulse port/hose as well.
seen some weird stuff with blocked one and cracked one

Hit the new impulse hose with air gun before installing, and hit impulse nipple with air while it was split. I will recheck before reassembly though.

 

[cus_deluxe]

honestly at this point it seems like all bases have been covered. id love to see a video.

 

[cus_deluxe]

View attachment 425242View attachment 425243View attachment 425244View attachment 425245View attachment 425246
So I pulled it apart, I don't see anything out of the ordinary... A couple marks on the intake side of the piston I can't feel them but I see them. I changed the intake boot to the new AM one. I slid it back together using motoseal instead of a base gasket (squish was .050 so plenty of room).
Now I wait until tomorrow afternoon and see what happens...

that mfer looks dry

 

[av8or3]

that mfer looks dry

Hadn’t noticed that. You’re correct , it ain’t wet. At least it looks that way.

 

[av8or3]

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?

 

[whybother]

that mfer looks dry

I wiped it out for the pics.

Hadn’t noticed that. You’re correct , it ain’t wet. At least it looks that way.

See above..

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'll have to look into this. Thanks