MS 660 Bogs Down When Warm?

Philbert · Apr 11, 2012

I know a guy with a well used 660 that he says cuts well when the saw is cold, but starts 'bogging down' when its been running for a while and warms up. The saw is used fairly regularly in a tree service.

Is this a symptom that could point to a specific fix?

One guy suggested that it might be worn rings?

Thanks.

Philbert

gsg · Apr 11, 2012

I had one that did that, it had a some what scored jug. When it got hot it would quit.

Adirondackstihl · Apr 11, 2012

Coil or tank vent are the 1st things that come to mind

Beer Gut · Apr 11, 2012

My fathers 029 did that, there was a small crack in the fuel line.

nmurph · Apr 11, 2012

The test for a vent is to crack the fuel cap when it starts this, and if it is the vent, the problem will resolve immediately.
Coils usually won't restart when hot, but seem to work ok when running. They do brown out when hot sometimes.
I would start with the checking the piston.

Philbert · Apr 11, 2012

Adirondackstihl said:
Coil or tank vent are the 1st things that come to mind

nmurph said:
Coils usually won't restart when hot, but seem to work ok when running. . . I would start with the checking the piston.

Fuel lines are fairly easy to replace. Vents are easy to check.

Is there anyway to check a coil other than swapping it out?

What would you check for on a piston? Are we talking about scoring or just compression?

Thanks guys.

Philbert

watsonr · Apr 11, 2012

Philbert said:
Fuel lines are fairly easy to replace. Vents are easy to check.

Is there anyway to check a coil other than swapping it out?

What would you check for on a piston? Are we talking about scoring or just compression?

Thanks guys.

Philbert

Your on the right track.... check it all just as you discribed.

nmurph · Apr 11, 2012

I have seen saws with cracked fuel lines not want to make full power, but I don't think I have seen one where the operating temp of the saw mattered.

Yes, look for scoring.

How long does the saw need to run bf the symptoms start?

Compression can cause hard or non-starting, but I would think that once a saw is running performance wouldn't change. The drop in compression from the motor warming up happens within a minute or so of start-up.

Philbert · Apr 11, 2012

nmurph said:
How long does the saw need to run bf the symptoms start?

Not sure of the specifics, but told him that I would attempt to gather some wisdom from the Oracles of A.S. and share that with him.

Philbert

albert · Apr 11, 2012

Fuel filter, clogged spark screen, fuel hose, too lean, piston/ring damage, dirty carb. A saw tuned right will be alittle rich on the first cut or two until it reaches full operating temp.

Philbert · Apr 13, 2012

Any other thoughts?

Any ideas on checking a coil?

Thanks guys.

Philbert

D&B Mack · Apr 13, 2012

I would check the tune first, could be near lean when cold then leaning out further when hot.

HEAVY FUEL · Apr 13, 2012

Never know, Is the bar getting oil????

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