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ms660 idle issues

zeroskater58

zeroskater58

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hey guys, new to the forum, been learning a lot reading all of everyones posts, just cant seem to find the info im looking for....maybe i havent dug enough. i want to prefeace by saying i am new to this, but very mechanically inclined....so i picked up an ms660, intention is to mill some timber on my homestead, used that had a scored piston and cylinder, looked like it had been run lean. still started and ran for the time it was demoed. i replaced the cylinder and piston with a big bore kit from ebay that was used and said to have low hours, figured sure since it should already be broken in. i opened up the outlet on the muffler as well. i have the service manual for the saw and followed the directions to replace the piston and cylinder. it started just fine after the replacement, but wouldnt idle right. i get it to a place where it sounds right, and holds idle when i tip it on its side as well, but if i leave it alone, the idle will slowly go down, and the saw will die. if i give it a little gas it will sometimes race after letting the throttle off and the chain will keep spinning. i say sometimes because sometimes it would settle to idle just fine. i know that the decompression valve is leaking, have a new one on the way. when i looked in the fuel tank there was a little saw dust, but the filter visually looked fine. would a bad fuel filter do this? it just seems like the saw slowly gets less and less gas at idle and dies, but the there are times it seems to randomly go lean and race. always starts back up just fine when it dies. havent checked the impulse line at this point. any suggestions on where i should turn my attention? as another note. there is no play in the crank that i can feel.

on another not, the bar oil at full throttle seems to not get to the bar, but comes out of the clutch cover, thinking the pump has a bad seal, am i on the right track? thanks for all your help and advice!

-danny
 
zeroskater58

zeroskater58

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Sure and leaks can come from other places.
any common places off the top of your head? i know i should check the impulse line, and the decomp valve is having gas pushed out, so maybe thats just it, we shall see i guess. any thoughts on why the oil would be coming out of te clutch cover and not getting to the bar? thanks!
 
zeroskater58

zeroskater58

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open the carb up at the fuel pump end
and look for clogged screen
checked the screen, its clear. im thinking its the decomp valve...i started it up today and afterwards there was the gas oil mix being pushed out from around the valve, not the threads, but the valve itself. thinking it might be losing compression a little to keep it from idling? read that these saws need good compression to idle. we shall see, part comes in tomorrow
 
lone wolf

lone wolf

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checked the screen, its clear. im thinking its the decomp valve...i started it up today and afterwards there was the gas oil mix being pushed out from around the valve, not the threads, but the valve itself. thinking it might be losing compression a little to keep it from idling? read that these saws need good compression to idle. we shall see, part comes in tomorrow
Lets hope so.
 
zeroskater58

zeroskater58

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been thinking about this, decomp valve is delayed because of memorial day, but if the cylinder does have a leak, would i be able to put a little motoseal on the gasket and bolt it up to seal it, or would that effect timing negatively?
 
zeroskater58

zeroskater58

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so update: replaced the decomp valve, pulled the cylinder again, and the mating surface looked a little scratched, so i put a little motoseal on both sides of the metal gasket, painted it on with a little brush. bolted it back up and let it set. started it today, it started 2nd pull, and seemed to be running much better. started to tune it after it warmed, and it started surging a little, not a crazy amount, but enough to hear and see the chain start to move and then stop, and then it shut off on me, and wouldnt start up again. i pulled the air filter off and pulled the fuel supply hose off the carb, and there was no fuel coming out. every other time ive pulled it and there is fuel in the tank, gas has come out. so i plugged the hose back in, turned the saw on its side, opened the gas tank and jiggled the fuel line. pulled off the fuel hose at the carb, and gas was coming out. thought okay cool, but the saw still wouldnt start. noticed that the wire coming through the grommet had been wrapped with electrical tape, so there might be a messed up wire there, but im not sure if its the spark or the kill switch. any ideas what it could be, or what i should check? thinking its a carb issue or fuel filter/line clogged..or maybe no spark? am i on the right track? thanks!
 
zeroskater58

zeroskater58

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well, cant get it started at all anymore. can pull and pull and nothing happens. pulled the spark plug, and its wet so i figure its getting gas. rested the spark plug against the cylinder and pulled, seems to have spark, but its not a fat spark like a cars would be,is this normal, or do i have a weak spark?
 
Tim Gordon

Tim Gordon

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I just had an Similar issue with my 044 where I had a vacuum leak between the carb and the intake manifold/boot
Sprayed some brake cleaner at the suspected area and the saw died
I put a new intake and I threw in a carb kit while I was there and that cured the problem
Being that the carb is attached to the fuel tank assembly and the intake gets stretched when using the saw it would cause a vacuum leak from time to time
Not saying that’s your problem but might be something to look at
I am no chainsaw expert but this helps
 
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zeroskater58

zeroskater58

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I just had an Similar issue with my 044 where I had a vacuum leak between the carb and the intake manifold/boot
Sprayed some brake cleaner at the suspected area and the saw died
I put a new intake and I threw in a carb kit while I was there and that cured the problem
Being that the carb is attached to the fuel tank assembly and the intake gets stretched when using the saw it would cause a vacuum leak from time to time
Not saying that’s your problem but might be something to look at
I am no chainsaw expert but this helps
thanks for the tip, man. intake boot looks in good shape to me, but i did notice that the saw is missing the little metal sleeve that goes in the boot, so maybe thats whats doing it. ill find out soon enough, got it on order.
 

stihl86

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You have to develop a more methodical approach You‘re all over the place, just chasing your tail.
You should establish if you have an air leak first. That’s done with a vac/pressure test.
Special tools are needed.
And there shouldn’t be ANY saw dust anywhere when you’re replacing a cylinder.
 
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