Stihl Echo SRM-225 backfire, won't start

cobra2411

LawnSite Member
Location
Honey Brook Pa
I have a Stihl SRM-225 trimmer that I'm trying to fix for a friend. He does commercial landscaping with a small crew. One of his guys was using it and said it just shut off and wouldn't restart.
I verified a no-start condition with high impedance on the coil. 35k or so from the high tension lead to the head. I pulled the coil and cleaned the connections. The resistance once off the trimmer was 2.7k.

I rest the air-gap, put it back together and as soon as I tried to start it it popped through the carb. I rechecked everything again, pulled the muffler in case it was clogged and same thing. As soon as I try it pops through the intake.

I suspect it sheared the key on the flywheel.

Am I missing anything?

Thanks,
David
 
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cobra2411

LawnSite Member
Location
Honey Brook Pa
In my haste to get dinner on does anyone see what I did wrong?

Anyway I fixed my mistake and I have a nice blue spark and no back firing. I also have no running. I tried a very quick whiff of starting fluid and nothing.


I'm going to get a new plug for it, but I did see a nice blue spark.

My reasoning says it should have at least popped with the starter fluid.

Give me any old 4-stroke any day... I apparently don't speak 2-stroke very well. It feels like it has compression, it has spark and it has a fuel that should burn. I Tried choke on, choke off, throttle closed / open and variations. Not a single pop.

At least with a pop I would move onto the carb. Could it have low compression?

Thanks
 

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cobra2411

LawnSite Member
Location
Honey Brook Pa
Ok.
~80psi compression
No spark on the spark gap tester. I tested it on my backpack blower and another trimmer and both jumped the gap. I also tried straight to ground vs to the plug and with the other trimmer it still jumped the gap but not the 225.

I guess I'm looking at a coil. Air gap is .010" and all connections are clean with no oxidation. To me a 2.7k ohm resistance is good but I guess not.

The magnets on the flywheel still work but I have no way to test if they're strong or not, just that the screw driver sticks to it.

Oh, I tested the stop switch and I also pulled the stop wire from the coil just in case. No spark.
 
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cobra2411

LawnSite Member
Location
Honey Brook Pa
Ok, I think I was right the first time. I thought I had put the coil on backwards and that was causing the pop. The parts diagram shows it with the high tension lead on the carb side and the ground on the exhaust side.

Anyway, I figured out how to get the clutch off. Shove some rope down the spark plug hole and jam the motor then take some big pliers and unscrew it. Key is fine.

Has to be a bad coil. I did see a spark at the plug but I guess it's too weak to fire under compression.
 

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