Echo SRM-251E troubleshooting

[Tyler Davis]

I picked up this Echo (gray) SRM-251E string trimmer second hand about 5 years ago, in very good condition. Used it for a year, then sat half full of gas for two years. Began effort to revive it with a repower kit and fuel line kit.
So new spark plug, air filter, fuel filter, fuel lines. Dumped old fuel and refilled with chainsaw mix (93 octane plus Stihl 50:1 oil) Got it started! Yes! Seemed to run OK, bogs a bit under throttle, twiddled with carb jets. Ran for about 20 minutes, at times it sounded healthy, other times it bogged under throttle. Then started cutting out on idle, only running on partial choke etc. Did some research, removed the muffler and cleaned the spark arrestor screen (very little carbon). Got it to restart intermittently, but dies after a few strokes.

What's the next step? Seafoam in the carb? Just buy a new carb and replace it? Tear down carb and rebuild kit? It is a Zama, not sure of the model number


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[Conquistador3]

If it were a Walbro, Tillotson or TK I'd say just soak it in pure acetone, dry with compressed air, fit new membranes and run it, but Zama's are notoriously a shot in the dark when it comes to rebuilds.
If you can find a cheap enough new carburetor, genuine Zama or Chinese clone, it would your best bet.

 

[Tyler Davis]

The owner's manual just lists "Zama diaphragm model w/ purge pump" - what is a good replacement part number?

I also see it calls for 89 octane gas. I have been using the highest octance I can find at the pump (usually 93?) because I was told it minimizes the harmful effects of ethanol. The 93 works fine in my chainsaw; is there a chance it is too rich for this weed whacker?

 

[Conquistador3]

Original carburetor is a Zama C1U-K81A.
It should be pretty easy, not to mention cheap, to obtain a C1U clone from China.

 

[Tyler Davis]

thanks for the part number. Once I replace this carb, should I switch to using racing gas or premix? My Stihl chainsaw doesn't seem to have a problem being stored with ethanol gas, but this Echo has been a royal PITA

 

[Conquistador3]

All my Echo equipment runs on regular fuel because 1)it's the only one we get here 2)I am cheap.
So far I haven't had a single fuel related problem.

 

[ANewSawyer]

Just don't leave the gas in it!

 

[Tyler Davis]

OK, got my genuine Zama replacement carburetor and installed it today. Good news is I got my trimmer started. First problem is that "idle" is now more like "half throttle" due to the fact that the throttle plate is depressed without even touching the idle screw. It's like the cable is too short, but I'm not sure how that could happen since the carb is an exact replacement. Once I get that figured out, I'll try to tune it

 

[Tyler Davis]

so it occurred to me while eating my lunch that there is an adjustment screw on the back of the throttle post that I can use to adjust the throw length. Duh.
Next question - do I install the limiter caps when tuning the carb? Is there any way to determine how many "counter clockwise turns" the screws were set to at the factory?

 

[GlynnC]

I would personally never reinstall the limiter caps. While running WOT (with string to proper length, set high speed jet by closing (clockwise) until engine slows, then open (counter clockwise) until engine slows, then back until full speed is achieved. While idling, set low speed for smooth idle and no hesitation going to full throttle. Adjust idle speed so that string head is not turning at all!!

 

[Tyler Davis]

OK, I got the throttle cable adjusted. Head does not spin at idle. I played with a screws a bit, trying to find the optimal point based on the sound and how fast it responded to the throttle. So it's running "fine" but I'm wondering if it can be improved. Would it be worth the effort to borrow a tachometer and use that to fine-tune the high-speed screw?

 

[GlynnC]

Do not set to highest rpm--2-cycle engines run fastest when set a little lean. If you use a tach, richer it up a little after finding the fastest rpm. I've set many trimmers being used commercially using the method previously described.