Throughly confused...

Soooo...

I was blowing lawn mowing residue from the driveway and the engine out of nowhere, decided to quit. Not even like it ran out of gas, just kinda wound down sputtered and spit and stopped running. Huh...

It acted like when you shear the flywheel key in a mower and lose timing and the only sign of life is a backfire.
Average 25cc 2-stroke engine.
Checked the flywheel for sheared key, fine. It's one of those cast in place ones.
Took the carb apart, both sides and the needle and it was clean.
Fuel lines intact, filter good, getting fuel.
Spark looked weak so I threw a $15 coil at it, spark looks better I guess.
New plug (2)
Disconnected the kill switch, then removed it entirely in case a wire was being pinched.

Normal start procedure, don't push the primer, close the choke, pull the cord and the only thing it does is backfire after a few pulls, then absolutely nothing other than a wet spark plug.

I do not remember for certain if I put a $10 ebay special carb in it, but I think I did about a year or so ago and about to throw another one at it out of frustration.
I went so far as to shoot some ether in it just to hear it run and nothing.

The backfire is what's really messing with me, if you've got anything I might be missing I'd appreciate it cause i'm stumped ATM.

I'm going to go do something else for a while and maybe I'll have an epiphany or something.

 

If ether doesn’t make it pop off its already flooded or you have a spark issue.

I assume it's a 2 stroke blower?

 

yes 2-stroke, at this point fairly positive i've eliminated everything else, so I guess fuel delivery it is. I'll have to close the needles off and try yet again, maybe that will get me somewhere. Tired of looking at it today, on to other things.

 

If you have fuel and spark then it must be a compression issue...or maybe crank seals...pull the muffler and get a look at the piston.

 

It's still got compression, had the motor out a few times now and took a look in the plug hole.

Pretty clean actually, not a ton of carbon buildup and nothing visibly apparent. The old plug almost looked like it came out of a 4-stroke, some residue buildup but no hard carbon.

Also pulled the backplate looking for clues and be sure o-ring hadn't sprung a leak. Everything seems normal, but obviously something is amiss.

I have to get a upper wisdom tooth out tomorrow early AM, decided to come out sideways at a 45deg angle so not sure i'll mess with it or not.

 

Spark arrestor plugged? Would think that would show up slower and not all at once though.

 

Three components, fuel, spark and air. Have you removed the air filter and tried starting it? Pull on the trigger so it's wide open and pull it some. I had it happen on a lawnmower recently where the filter clogged and it would not restart. New filter and we were good again.

 

That backfiring to me sounds like the spark is going off when the piston is not at top dead center, like it somehow lost ignition timing. Almost like there's something up between the flywheel and the stator, and its sending the signal to the coil at the wrong time.

 

Checked that also.

 

Hey fellers, I'm short on time this AM please re-read OP. PS; I bought a $14 ebay carb so it should be here in a few. Used to re-build them until the kit price and time involved exceeded buying a whole new one.

 

If it were me, I'd be pulling the muffler to have a peek at the piston and ring. Can you perform a compression test?

 

Cracked ring comes to mind. Just a spit ball though.

 

I got fed up with mine and got a battery unit. Good enough for what time I want to spend leaf-blowing.

 

Have not pulled the muffler yet, however from messing with it and putting in the new coil, along with pulling the rope, it does not feel any different that it has ever been.

 

I started messing with small engines when I was about 10 years old, with a Cox .049 (that spiraled out of control for decades!)
Been messing with all sorts from big to small, gas, diesel, and propane ever since.

The little weedie engines are reliable, strong, and last a long long time with preventative maintenance.

Right ATM I just haven't looked in the right place yet, but when I do I'll just be that much smarter. (IMO)

 

I think I looked in the right place...

So digging deeper I pulled the jug off, and despite my previous accolades, the piston is indeed a carbon fouled mess.

Ring was stuck tighter than a frog's butt, and careful wiggling with applied ATF and/or "carbon cleaner" did little to unstuck it. So I did the right thing and forced it, which of course broke the ring, and yet still refused to come out in anything more than in 1/2" pieces.

All is not lost though, I bought a two-pack of rings on good ol' fleabay for $10.

Had I bought only one ring, you KNOW I'd break it installing, so I got two for a couple bucks more. lol

I always choose "closest first"and provided their not lying about the shipping location I might have it in a couple days. Sleazebay likes to lie about shipping in order to prop up sellers from California, leads to weeks long delays going to the other coast where I am. They need the same lawsuit that is being leveled at scamazon brought against them (IMO)

The carburetor I bought said it was shipping from NJ when I bought it, and when I got the shipped conformation, it is now coming from ...you guessed it... California which means I won't see that until next week now.

 

Probably don't need the carb anyway?

 

Likely at this point.

The (first) one I bought on sleazebay was cancelled by the seller stating "shipping address problem" which is impossible because I use paypal.

Come to find out he jacked the price $5 after I purchased, so it's obvious he cancelled the order because he didn't want to sell it at the price I paid.

 

Still thoroughly confused...

Put the new ring in, new carb showed up early so why not, new coil, new plug.
Coil .010 spark plug .025
Cylinder looks good enough, I know what it looks like when the chrome decides to leave the building.
Key is intact on fly wheel indicating it cannot be out of time. Magnets pass coil right around TDC seems about right..
All appropriate gaskets/O-rings in place.
Plastic backplate not cracked or broken.

Pull pull pull, nothing. Got sick of pulling and hooked up one of my drills to the nut on the crankshaft holding the fan on, still nothing. Oh wait ...I'm an idiot... fuel lines backwards.

Finally starts hesitantly and weak, will only keep going at low partial throttle and any needle adjustments make it quit. Swap to old carb, same result and I notice it gets hot, too hot fast. All symptomatic of timing or too lean, but both carbs act the same.

Fine... I completely disassemble again, this time I knock the crankshaft out and find there is zero possibility that the counterweight to output shaft relation can move, which would throw off the flywheel keyway.

I notice the crank seal is kinda not the best and getting stiff, but not real bad either, fine... for $6 I'll toss one of them at it too.

Other than that there's not much else to replace.

On the other end of the spectrum, I found a Echo SRM-230 straight shaft string trimmer in the dump that needed, well nothing really except gas.
Didn't want to start so gave it shot in the carb and it fired right up. Tank smelled like old, really really old gas and the primer didn't want to work from gumming residue.

I kept pressing it to wash fuel through, started it and I had to balance the choke to throttle until enough gas washed through to get the passageways back open, and it runs great COOL!

Of course the primer bulb gave up and split, but I ran it long enough to make sure everything worked like it should before ordering parts. Tune up kit with spark plug, fuel, air filters. A new primer bulb and rubber gas tank grommet that the fuel lines pass through, and the engine cover is discolored so for $8 I got one of those too.

Now I need to find a Echo leaf blower.

 

Did you do a pressure vacuum test?
I see you only did 50% of the crank seals.