HELP! MS 660 carb issue

[whybother]

I have an ms 660 I'm working on for a guy. While tuning the carb the low side tuned just fine, the high side is needs to basically be closed to get anywhere close to max rpm. You guys have any ideas why this would be?

I don't know the history of this thing and am wondering if someone may have drilled the low side jet or something similar. It idles and revs up normal just high side adjustment does not make sense to me.

Saw was not running when I received it. I put a new oem cylinder and piston on it along with new crank bearings, gaskets and seals. No performance mods just a muffler mod.

I'm stumped, any advice is appreciated. Thanks

 

[Dolkitafreak]

I have an ms 660 I'm working on for a guy. While tuning the carb the low side tuned just fine, the high side is needs to basically be closed to get anywhere close to max rpm. You guys have any ideas why this would be?

I don't know the history of this thing and am wondering if someone may have drilled the low side jet or something similar. It idles and revs up normal just high side adjustment does not make sense to me.

Saw was not running when I received it. I put a new oem cylinder and piston on it along with new crank bearings, gaskets and seals. No performance mods just a muffler mod.

I'm stumped, any advice is appreciated. Thanks

Is the metering lever set to the proper height?

 

[Woodwackr]

Rebuild the carb?

 

[whybother]

Is the metering lever set to the proper height?

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

Rebuild the carb?

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.

 

[Woodwackr]

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.

If you have a sonic tank, Disassemble including the needles and run in carb cleaner. I use Berrymans since they sell it in non-spray bottles...I get it by the case

 

[cus_deluxe]

are you sure metering side is put back together correctly? diaphrams in right order i mean

 

[Poleman]

Does the carb hold pressure? 7 lb? Could be a leaking Welch plug letting fuel by on the low side or nozzle could be bad. There’s extra fuel coming through the low side if you can close the High.

 

[whybother]

If you have a sonic tank, Disassemble including the needles and run in carb cleaner. I use Berrymans since they sell it in non-spray bottles...I get it by the case

No sonic tank yet, it's on the list though. I'll have to remember the Berrymans tip when I get one.

are you sure metering side is put back together correctly? diaphrams in right order i mean

I was 99% sure before, 100% sure now after I ripped it apart again to double check stuff.

Does the carb hold pressure? 7 lb? Could be a leaking Welch plug letting fuel by on the low side or nozzle could be bad. There’s extra fuel coming through the low side if you can close the High.

I thought of this too. It held 7 lb for 5 minutes. I don't think I have anything to measure the nozzle with.

 

[Poleman]

Good that it held pressure. Your nozzle should be good then. If you don’t have an Ultrasonic Cleaner break your carb down and put in a jar with fresh fuel and let it soak overnight. I have an US and when I can’t get a carb cleaned out that’s what I’ll do especially on older antique saws you can’t get anymore or a carbs that’s had a lot of corrosion in it.

I’m presuming this is an OEM carb. If it’s aftermarket a lot of those run way rich an/or are hard to get correct.

 

[whybother]

Yes it is an OEM carb. I got burned on an aftermarket one once, won't be doing that again...

Debating soaking in fresh fuel only or what my friend calls a Cass County cocktail (mix of Berrymans, seafoam,, marvels mystery oil, and mixed fuel).

@Mastermind is right chainsaws are dumb...

 

[av8or3]

I have a new OEM carb for that thing I’d like to re-home.

 

[drf256]

How does it tune without the airfilter installed?

What’s your altitude?

Have you checked the ignition timing?

Does the saw seem to have power in the cut?

 

[av8or3]

Very early on in my chainsaw experience I too had a 660 (066) that would not tune. I put a kit in the carb and no change. Replaced it with a new carb and “fixed”! I work a little harder on them these days, but then, not so much.

 

[whybother]

I have a new OEM carb for that thing I’d like to re-home.

I'll PM you, might need it if soaking for a couple days doesn't change this ones attitude.

Very early on in my chainsaw experience I too had a 660 (066) that would not tune. I put a kit in the carb and no change. Replaced it with a new carb and “fixed”! I work a little harder on them these days, but then, not so much.

I'm far from giving up on this carb. It's just testing my patience, I need this tuned and outta here...

 

[whybother]

How does it tune without the airfilter installed?

I did not try this, carb is soaking now. New air filter installed during rebuild

What’s your altitude?

1482 above sea level

Have you checked the ignition timing?

Key is new. pulled the flywheel nut and everything is where it should be yet.

Does the saw seem to have power in the cut?

Haven't cut with it, it's not tuning properly so I did not see a point in that I guess

 

[Chainmale]

If you have a sonic tank, Disassemble including the needles and run in carb cleaner. I use Berrymans since they sell it in non-spray bottles...I get it by the case

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

 

[whybother]

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?

 

[drf256]

Intake boot?

You’re not getting enough air somehow.

I’d pull the jug at this point.

 

[whybother]

Intake boot?

You’re not getting enough air somehow.

I’d pull the jug at this point.

OEM intake boot, I checked it throughly before reuse. No saying I didn't miss something... I have no problem pulling the jug. What am I looking for though? Thanks for the help and advice Doc.

 

[drf256]

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.