Echo SRM 266, Im stumped.

[scmoose]

I'm at a loss with this trimmer. Sounds as though it has a miss, or backfire at WOT and will not reach top speed. Starts and idles fine. Started when my son bought the unit, ran fine for a day, he stopped it, replaced cutting string on the head, when he restarted the unit is when it showed this symptom. What I've done.

-Replaced coil no change. cheap amazon version
-Replaced Carb no change. cheap amazon version
-Replaced plug and fuel lines and filters.
-Compression 140
-Checked flywheel key
-Pulled cylinder inspected for damage to piston, ring and walls, all look good. Small amount of carbon on top of piston, cleaned it off.
-Inspected pass through ports in cylinder, no buildup.
-Removed exhaust screen, inspected exhaust port, ran with muffler, same symptom.
-Removed kill switch wire from coil pack, no change.
-checked for leaking gaskets around carb by spraying starter fluid around the carb while running.
-several tanks for fresh fuel, pre-mix, and self 50:1 mix.

 

[redneckhillbilly]

fresh fuel? did you try getting some new stuff yet
maybe a magnet on the flywheel has a crack.

 

[scmoose]

fresh fuel? did you try getting some new stuff yet
maybe a magnet on the flywheel has a crack.

Yes, several tanks of fresh fuel, premix, and self-mix. I didn't pay attention to the magnets on the flywheel other than rubbing a piece of scotch Brite over them. Ill remove the cover and look closer at them.

 

[David Young]

when you replaced the coil was the plug lead included? possibly worn through and shorting out? Color of plug? is it not getting enough fuel? run without air filter, with out muffler. Gravity/bottle feed fuel. run in the dark and see if it is shorting out somewhere.
try removing as many variables as possible

 

[hacskaroly]

Replaced coil no change. cheap amazon version

Does the coil have the correct gap (either with feeler gauge or business card)?

 

[scmoose]

when you replaced the coil was the plug lead included? possibly worn through and shorting out? Color of plug? is it not getting enough fuel? run without air filter, with out muffler. Gravity/bottle feed fuel. run in the dark and see if it is shorting out somewhere.
try removing as many variables as possible

Yes, the coil came with its own plug lead attached. I've run without air filter and muffler. I haven't gravity fed. I wish I could post a video here to show what it sounds like when running. I will pull plug and post a picture of it.

 

[scmoose]

Does the coil have the correct gap (either with feeler gauge or business card)?

I set the gap with a business card. I have removed the Amazon coil, that exhibited the same exact symptoms as the OEM coil and returned it since I didn't feel that was the issue since it did the same exact thing.

 

[hacskaroly]

I set the gap with a business card.

Good to know, I figured you did, just wanted to eliminate one more thing that it wasn't. Yeah, this one is a stumper!!

 

[scmoose]

fresh fuel? did you try getting some new stuff yet
maybe a magnet on the flywheel has a crack.

Just looked at the flywheel magnets, no discernable damage or loose magnets.

 

[scmoose]

I've already brought it to one small engine guy, who also came up with nothing. I did stop him short of tearing it completely apart want to avoid higher service fees than what the unit is worth. Still cost me 50.00 for him not to be able to figure it out, he had it for 3 weeks, not that he worked on it that long. He did tell me that he had compression at 90 psi, but my set of gauges had it much higher at 140.

 

[David Young]

I've already brought it to one small engine guy, who also came up with nothing. I did stop him short of tearing it completely apart want to avoid higher service fees than what the unit is worth. Still cost me 50.00 for him not to be able to figure it out, he had it for 3 weeks, not that he worked on it that long. He did tell me that he had compression at 90 psi, but my set of gauges had it much higher at 140.

Does the piston look good?

 

[scmoose]

I felt it did. Little bit of carbon but it cleaned off fine. There is a small hole, not through in the top center of it, but looking at pictures that's part of the casting.

 

[EFSM]

Could you post a video of it?

 

[EFSM]

I suppose it could be both the original and Amazon coil are bad.

 

[Firewood Hoarder]

Does the cutting head and shaft spin freely? It seems strange that the problem would come up after reloading the head with line. Is it possible that the head is binding up?

 

[beaglebriar]

Have you pulled the flywheel? Is the key in good shape?