2-stroke won't rev. Thinking carbon/exhaust port?

[sd455dan]

When my SRM 300 wouldn't rev it was always carbon on the spark arrestor screen...

Yes- but he stated he already removed and cleaned the mufller and the spark arrestor said they are clean Post 11

 

[ultrarunner]

Not sure how I would clean my muffler because it does not come apart...

What about testing it without the muffler/spark arrestor?

 

[sd455dan]

yeah , never tried to clean the actual muffler on any saw or spin trim either- and the spark arrestor only 2 times since the trimmer was new in the 1980s .
these Echos seem to last a very long time- ours only major failure has been one magneto coil, and it WAS a little pricey...other than that it has been pretty bullet proof :thumbsup:

 

[ultrarunner]

Mine is down right now... fuel tank is bad and no longer available.

Echo said they phased out parts for all the non-carb compliant stuff and I'm in California...

One of these days I will fab up a replacement.

 

[Welshman]

Not sure how I would clean my muffler because it does not come apart...

What about testing it without the muffler/spark arrestor?

This happens to me every couple of years, and my muffler/spark arrestor doesn't come apart either. I submerge mine in lacquer thinner for a few days and it's like new. I drain it and set it out in the sun for a while to make sure there is no lacquer thinner left in it.

For the style that comes apart, just burn the carbon off the screen with a propane torch.

 

[canucklehead]

I clean spark arrestor with a wire brush. Muffler I remove and spray brake cleaner than bang it around and knock out loose any crud. I also blow compressed air thru it.

how do I remove the string holder part? I can remove the entire head. is it okay to rev it up while the shaft is flopping around with nothing connected to it?

I still have the guard and it keeps the string at the proper length as the metal piece will clip spinning string.

 

[sd455dan]

IIRC you remove the clamp bolt that tightens down on the exterior shaft , then the drive cable should slide out of the centrifugal clutch housing . unless mine is different or i am not remembering correctly- the drive cable should slide out of the clutch unit if pulled on...leaving only the electrical connection (on/off) and throttle control.
If the engine can be started and revved up (it won't have the flywheel effect of the driveshaft/ trimmer head) and will accelerate much quicker, you can be fairly sure that the grease and other lube is to viscous causing to much load and keeping the engine from reaching full rpm, if it cannot be revved up then there must be some problem with the engine itself but it will eliminate the driven part of the trimmer.
if ours had not acted identically to the symptoms you described i wouldn't have you test the engine with the drive disconnected

 

[canucklehead]

oh, so you're suggesting disconnecting drive cable at top of engine vs. the bottom?

 

[sd455dan]

oh, so you're suggesting disconnecting drive cable at top of engine vs. the bottom?

Yes i believe the main shaft clamp bolt can be loosened, then the flexible drive line pulled out of the centrifugal clutch. The on off switch and throttle will still be attached to the shaft and trimmer end. Holding the engine on a table or other support start the engine and if it will rev you will know that friction in the bearing and gears do to thick grease and oil is to blame... Now-
If it won't rev the engine itself has the problem, but this test should confirm or eliminate the driven end as the problem.