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Peak Industries


stihl ms660 won’t start

LetTheChipsFly

LetTheChipsFly

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gday from Australia fellas

righto my problem started a couple days ago saw ran fine for about an hour and when it got hot it wouldn’t start up i’ve been through the basic stuff seems to be getting spark fine cleaned the carby although when pulled fuel floods out of the muffler i’ve taken a few photos of the piston what’s your thoughts
 

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president

president

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Check the inlet needle ,and passage in the metering chamber
1 turn out for both high&low ,richer on high if muffler modded
mabey choke plate sticking closed?
 
brock1994

brock1994

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Straight gas would be my first guess. Then running to lean would be my second.

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rmh3481

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Its hard to tell sometimes by looking thru the exhaust port. Ive seen worse run well. A scuff on the skirt that doesnt run up through the ring lands is usually nothing to worry about. I do see other marks around the top of the piston, so at this point its about the cylinder. Has it been rebuilt before? Chin Parts? I think you should run a compression test (psi) on it and then go from there. If its new to you and had an offshore piston put in it for sale, I think you know whats up.
 
brock1994

brock1994

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Maybe it was running to rich and excess carbon build up fell off the combustion chamber and caused the scoring on the piston. Like everyone said I would pressure and vac test and then go from there. Definitely needs new piston and rings at very least. Good luck hopefully you figure it out.

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drf255

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Chi-wan-Eeze Cylinder?

Your missing some plating there. I woulda thought your piston was ok to run, honestly.

It’s good you tore it down.

If the saw still had plenty of compression, I was gonna say to check the coil after changing the spark plug. No spark will flood a saw up as well.
 
Ando81

Ando81

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Hi mate, another Aussie here trying to share some things I’ve learnt. Is the cylinder stamped with Stihl on it somewhere? I’ve heard that Chinese cylinders can have a sharp edge on them at the ports and can cause them to grab the ring on the way past if the carby leans out. Saying that, I bought my Jonsered 2165 with piston damage like this and it wouldn’t start. I pulled it down and cleaned the piston, rings & cylinder up so it was free of aluminium again. It now runs fine and hasn’t let me down yet. My saw had more damage on the piston to the extent that the ring was stuck to the side of the piston and had to be persuaded to come free from the piston. I’d try cleaning it up carefully first and assemble it to do a compression test, making sure that the ring gap isn’t lined up on the skirt like in your photo. I’ve heard that it’s not ideal to have the ring gap in line with the skirt. Good luck mate
 
LetTheChipsFly

LetTheChipsFly

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Chi-wan-Eeze Cylinder?

Your missing some plating there. I woulda thought your piston was ok to run, honestly.

It’s good you tore it down.

If the saw still had plenty of compression, I was gonna say to check the coil after changing the spark plug. No spark will flood a saw up as well.
yeh after having a good look at it the cylinder definetly isn’t OEM ive binned it and ordered a genuine one already along with a new spark plug coil and a new walbro carby i picked it up dirt cheap so expected some issues only thing i never did was run a compression test before pulling it all apart so hopefully there’s no other dramas
 
Ando81

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Yeah it’s probably going to be a lot more reliable to have high quality parts put back into it. I’d rather do it right the first time than always be doubting its reliability.
 
LetTheChipsFly

LetTheChipsFly

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Yeah it’s probably going to be a lot more reliable to have high quality parts put back into it. I’d rather do it right the first time than always be doubting its reliability.
yeh mate don’t wanna stuff around with crap parts i don’t run any on all of my saws old mate i picked it up from said he had the cylinder and piston replaced not long before i picked it up off him so im still not 100% sure it’s the main issue i got it cheap so either way at the end of the day it’s gunna be a reliable saw that doesn’t owe me more than it should
 
Ando81

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I’d be making the carb run a bit richer to be safe as a starting point. Don’t want to risk a new piston if someone has set the carb to run lean
 
Gord404

Gord404

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Fixed a 660 a while back, gas flooding when hot and yours probably got good and hot, because of the tank breather that is one way in and won't let pressure out your carb has to hold the pressor back and if its getting past the needle, well floods the engine, at the least it needs a carb rebuild and a new top end and a vac- press test when all is said and done.
 
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