MS660 Dies under load

[AaronB]

My MS660 started dying when it touched the log or you put it at full throttle, it will always start right up and idle just fine. I had a neighbor put a new carb on it for me, it started right up again, I made about 5 cuts with it and no problems.

I set the saw down for about 15-20 minutes and again it started right up, but when I went to cut the next log it died as soon as it hit the wood, started it again and same thing, started it again and pulled the throttle to full and it would die. Idles just fine, starts just fine.

This is the second time this has happened, both times a new carb was put on, both times it worked for about 5-6 cuts then starts dying under load.

What's the next thing to check? I may just end up taking it to a shop to get it straightened out.
Thanks

 

[Chainsaw Jim]

Replace the fuel filter and fuel tank vent and make sure the air filter is clean.
Avoid ethanol fuel and make sure your fuel is fresh.

 

[rd35]

Put a new spark plug in it. This happened to me on two different saws. Plug gets hot under load and gets a ground fault internally. Easy thing to try. Put a new spark plug in it and give it a try....I bet you will be pleasantly surprised!!!!!!

 

[bacon K5]

Agree with what Jim said, but I'll add to check your impulse line/fittings for cuts or blockages. If it is blocked or cut, most saws will start and idle just fine but will die when the throttle is opened. It's possible that if it was a small cut or blockage, it may take a little time for it to lean out to the point of stalling. You could also check the metering lever for proper adjustment, but that seems like a stretch.

 

[AaronB]

Replace the fuel filter and fuel tank vent and make sure the air filter is clean.
Avoid ethanol fuel and make sure your fuel is fresh.

The fuel filter "looks" fine and neighbor thought so too, but I have another one I can put in.

I did buy ethanol free gas this year so I know it's good.

I'll have to look for and get a fuel tank vent, not real familiar with the saw yet so I don't know where it is our how to replace but will research it.

I just find it weird that it works for 5 cuts then starts acting up, guess it hearing up can cause the filter or vent to start acting up?

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[Adirondackstihl]

Just went through the EXACT issue with a 346.

Plug was loose enough for the gasket/washer to dance around while the saw was running.
Snugged the plug and all good

 

[blsnelling]

Tank vent.

 

[rd35]

.......spark plug........

 

[grizz55chev]

Coil!

 

[Gugi47]

I have to say tank vent.
But can be the plug to.

 

[AaronB]

I went and bought tank vent, spark plug, and filter. I replaced only the vent, started right up like normal and I ran it full throttle up and down and it didn't die.

I ran it up and down the throttle for a few minutes then let it sit for 15 minutes, restarted it and it went to full throttle without dying, so that's better than what it was doing, just needed to male some cuts to really test it.

Hopefully it will last to mill the last log of the season with the Alaskan. If it acts up again then I will try spark plug next, just trying to narrow down the cause rather than changing everything at once and not knowing what fixed it.

Now see other thread for 361 issues.

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[o8f150]

first thing i would do is pull the muffler and check the p/c and run a compression test

 

[rd35]

Well, sound like you are on the right track.

If it acts up again then I will try spark plug next, just trying to narrow down the cause rather than changing everything at once and not knowing what fixed it.

AaronB, I like your approach to diagnosing a problem. You will get to the bottom of it in a hurry this way!

 

[AaronB]

Btw, what does the tank vent do and how does it get messed up that it needs replaced?

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[Chainsaw Jim]

It allows the fuel to flow from a sealed container without going guckle guckle guckle. Lol
If you bought a new fuel filter then don't wait for the old one to act up, just change it now.