Crapsman string trimmer stalling

[FergusonTO35]

That o-ring is a cheap and easy fix. Maybe try it before you call it totaled?

 

[Leafy]

Yeah. I'm going to measure it. I can buy a 50 pack off Amazon for what the shipping it for the actual part number.

 

[Fish]

It is a Ryobi/MTD trimmer.

 

[AVB]

Before going a lot more trouble check the cylinder condition or at least a compression test as you need at least 100 psi for it to run and closer to 120 for it to run right.

 

[Leafy]

Rings and cylinder look fine, from what I can see looking in both ports and looking up from the crank case. Its got plenty of power in between the misfires. If the oring doesnt fix it I'm just going to assume the crankshaft is bent or the flywheel hole is off center and thats causing a speed wobble that makes the magnet go far way from the coil only at high rpms.

 

[AVB]

Rings and cylinder look fine, from what I can see looking in both ports and looking up from the crank case. Its got plenty of power in between the misfires. If the oring doesnt fix it I'm just going to assume the crankshaft is bent or the flywheel hole is off center and thats causing a speed wobble that makes the magnet go far way from the coil only at high rpms.

All I know on misfires recently has been two srm225 Echos that the rings were max end gap and the cylinder plating worn through plus the piston minimum OD was below minimum spec. They ran fine at idle but miss fires at full throttle. Wasn't a coil as I had a coils from two other srm225 that had other problems from being left out in the rain. Just too piston wobble at full throttle. Just too costly to rebuild as Echo only offer short block for these when it get to the cylinder replacement.

Now bearings do go bad allowing the crankshaft to push on the seal opening the opposite seat which could cause a miss fire. And I have seen coils to do crazy timing of ignition at time as I had Homelite chainsaw that set the air filter on fire at times.

 

[FergusonTO35]

And I have seen coils to do crazy timing of ignition at time as I had Homelite chainsaw that set the air filter on fire at times.

Interesting, a Homelite Super XL spontaneously combusted on my dad when I was a kid. He never figured out what the cause was.

 

[smokey7]

Speaking of coils doing funny stuff i have one of my 2 homelite ranger 33 cc saws doing funny stuff. It will fireidle and rev fine. Then let it idle for a bit it will then idle lower then make a spuff sound and then run backwards. Swapped coils from saw to saw and the same problem followed the coil to the next saw.

 

[FergusonTO35]

Wow. I've known of engines that could be run backwards by design such as golf cart engines but I wouldn't think a coil alone could do that! Of course, you could make a Detroit 2 stroke diesel run backwards on accident too.

 

[AVB]

Actually any 2 cycle is capable of running backwards but most time modern coils will not fire in reverse. Now the engine has a problem that causes dieseling it can run backwards it get bump at the right time. And I have seen a 2 cycles running on gasoline/oil mix to diesel. Matter of fact I had a HS56 that was diesel after warm up so bad that even the coil's rpm limiter was shutting the spark completely down but when I returned to idle the coil took back over.

I had took it in for the dealer to fix under warranty and after 3 weeks they return it saying nothing was wrong with it. I ended up fixing it myself and charged customer under non-warranty repairs.

 

[Leafy]

On this trimmer, oring no fix. I'm thinking it's the bent pto or offset flywheel making it whip at high rpms and cause the magnet gap to open up. Like if I crank it rich to where it only revs to 6k and 4 strokes it runs fine, same if I have it tuned normal and only just crack the throttle. That puts this right in the *f-wordit bucket, not worth the effort for an 80 dollar string trimmer.