I have fixed dozens of 2 stroke motors but this one has me baffled (#1, model: 358.794941). I happen to have a very similar one that I just fixed (#2, MODEL#: 358.797550). #1 Won't start, but it does have a big spark. If I switch #1 carb to #2, it works fine on #2, so it's not the Zama carb. Same for the spark plugs, they both work on #2, but not on #1. I never get a hint of firing on #1. I took the muffler off, no impact. I can blow through the muffler, it's not restricted. I put new gas in #1 from the same source as #2 that is working fine. What's next? Normally I can deal with a bad carb, or no spark, but this one has me stymied.:(

Hi,
Two things I will say are that the piston rings could be stuck on the exhaust side (did you look when the muffler was off?) and that the keyway to locate the flywheel in the correct timing position is cast in and can shear (which I would say you have here!)
Peace,
Clarke

More data I just gathered: Blower 1 that won't fire yet has spark only has a compression reading of 80. Blower 2 that runs good with either carb has a compression reading of 120, with the same gauge. Should I proceed to check the flywheel, or is it just junk?

Do the compression test again with some oil in the cylinder. An increase in pressure with oil usually means bad rings, otherwise the valves.

I can see the ring on the exhaust side, the muffler is still off. It seems to be in place and moving with the piston.

With oil in the spark plug hole, the compression reading on the bad blower goes up from 80 psi, to 100 psi even. Does that mean a new piston ring would mean it would run? If so, I might do that, but check the flywheel key for slippage before I get that far. The good running similar blower had a reading of 120 with no oil, and only went up to 125 with oil. After all this carb switching and oil, the good one still just started on the first pull. By the way, the problem with the good one that I fixed was a loose cylinder. One of the 2 bolts was loose, allowing a gap on the carb side of about .020".

I took Crigby's advice and tooke the flywheel off. There is no key, it is cast into the flywheel, and it is properly aligned. I took the piston out and the ring is like stuck in the groove, and not sticking out at all, it's the same diameter as the piston. Other than that, everything looked OK. I tried to get the ring out, but it broke apart as I proceeded, it was really jammed in the groove with black crud.

Hi,
A new one at Sears is under $4.00. It is part #530055120. Use a piece of the old ring to scrape the groove clean.
Peace,
Clarke

Unfortunately, the actual cost at Sears is $11.45, when they add shipping and tax, even if I go to the store to pick it up. If they could think outside the box, they would appreciate that since it weighs about one gram, it could be sent in an envelope for 42 cents, but that would violate policy.

I put in a no hurry, no special shipping cost request at my local small engine repair shop, and they will call me when they get their next batch order. Thanks for the help.

It's a typical problem. Part is so cheap, so it makes sense to pick up at a local dealer who gets regular shipments.

SPD parts are the wrong ones. They won't fix it even after calling. You have to order 5 from manufacturer. I had to do that with Hypro keys. They sent me a Woodruff key. The third in the mix is a non-rock key. I learned something.

I needed a specific diameter cotter pin. Local places, including commercial and kits, skip that diameter. Had to get 10.

I needed something is 6-32 Carriage bolt. Had to buy 100.

Hi,
Know the feeling! Needed a very large castellated nut once and it was near impossible to get in a single, and my boss would have never used the other 24.
I have had a different experience with Sears if the part was already local; you can search on the website to see if it is.
Peace,
Clarke