stihl 660 trouble

[wildwoodford]

saw runs great untill it gets warmed up. Then it looses power slowely, and eventually just dies. Starts right back up, runs good for about a minute, and then proceeds to slow down and die again. Has a new cylinder, piston, and rings in it. Air breather is clean. spark plug is gaped, with no signs of excessive oil mix, or corrosion problems. Any body have any thoughts or helpful pointers? might be a husky man yet if this foolishness keeps up.

 

[Wood Butcher]

My first 2 thoughts are to check the fuel filter in the tank and also the ignition module. If you can cut some wood by an air compressor, and then when it starts acting up spend 1/2 a minute bowing off the module with compressed air to cool it down and see if that makes a difference.

 

[pioneerguy600]

Give the tank vent a close inspection, the fuel tank may be getting airlocked.

 

[tallfarmboy]

Fuel tank vent as said, or possibly a coil that is failing when hot.
Sounds like a bad coil to me, possibly.
TFB

 

[twoclones]

How does one test a coil? Measure resistance?

 

[tallfarmboy]

When the coil is failing in that manner, it is almost easiest to find another saw and swap coils. Do you have access to another saw with the same coil?

 

[AKDoug]

It shares the ignition module with 046, 066 and 460 if you know someone with one of those.

 

[fearofpavement]

If the saw is slowly dying, it probably isn't an ignition problem. When the ignition gets hot and cuts out the saw will usually quit like you hit the off switch.

On a new rebuild, make sure the piston isn't too tight in the bore. Is it hard to pull over after it quits or does it feel normal?

Otherwise I vote with the fuel flow crowd. (try a new filter in the tank, check the fuel hoses for leaks, check the fine screen in the carb for fuzz, try running it with the fuel cap loose, etc)