Echo CS-4600 - Saw dies when hot

[BDH]

I have an echo CS-4600 that dies and has a difficult time restarting after getting hot. I only get about 1-2 minutes of use before it starts this behavior. Once I get it restarted after it gets hot, the motor bogs/dies when throttle is applied. Additionally, the saw will die when idling after it warms up. One interesting observation is that I could get the saw to run okay enough for 10-15 minutes if I ran it at 3/4 to 1/2 choke. But eventually, this would not work.

I've read forum posts on this site related to this behavior and I've tried the following:

1. Took the carb apart and cleaned it out. The seals and diaphragm still looked good and there were no noticeable wear or tears.
2. Replaced the spark plug and checked for spark. Seems to be okay.
3. Checked for leaks in the fuel line and crank case pressure line. Seems to be okay.
4. Cleaned out the tank vent. (Actually tried removing it to check if it made a difference but no change.)
5. Checked the compression using an Innova compression tester from Advanced Auto Parts. I did ten pulls with the throttle open when cold. I got anywhere between 130 and 150 PSI. The factory service manual says 130 PSI. I redid the compression tests after the saw warmed up and the compression test yielded nearly the identical pressure reading. I checked the pressure gauge against my air compressor and got within 5psi, so I'm fairly confident that the gauge is fairly accurate.
6. Inspected the piston and 2 rings via the exhaust port. There is some scoring on the piston but the rings are still free and not seized to the piston.

I'm a little leery of the compression test. The first pull it goes to about 90psi and by the fourth pull it's at 150psi. Subsequent pulls do not change the pressure. I'm not sure why I'm showing a higher pressure then the factory manual. I'm not sure about the history of this saw, it was given to my dad by my uncle who owns a small engine repair business about 10 years ago.

Any insight would be much appreciated. My next steps would be to buy a carb rebuilt kit and then pull the cylinder and inspect it more closely.

Cheers!

 

[J D]

After what you've done & from what you're describing I'd be doing a vac/pressure test on it.

 

[medalist]

Also, run it with a neon spark tester in line to rule out a hot ignition component issue.

 

[lone wolf]

After what you've done & from what you're describing I'd be doing a vac/pressure test on it.

And then replace the coil if that passes.

 

[J D]

Agreed, sometimes a coil will become problematic as it warms up... Running a richer mixture (ie, choke partly out) could delay the onset of symptoms as the richer mixture doesn't require the coil to "work" as hard to create a spark.

 

[J D]

If you can't access a pressure/vac or inline spark tester you could run the saw till the problem presents then immediately plug the lead on to a spare known good spark plug, ground against cylinder & check condition of spark. Gapping the plug a bit wider (~0.8mm) should make any issues more apparent.

 

[BDH]

JD, thanks for the suggestion. Looking into it, seems like the endeavor.

I might try out the neon spark tester first since it looks easier to do.