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Discussion Starter · #1 ·
I got a Craftsman Blower mod: 358.794741 that will not start. I have spark to the plug and it seems to be getting fuel to the plug also. I have checked everything it seems like. Vent in gas cap, cleaned carburetor replacing gaskets and diaphragms, muffler restrictions, new gas, checked fuel lines for leaks, checked fuel filter in tank, adjusted and re-adjusted carb settings. I even squirted a couple shots of starter fluid in the cylinder with no reactions. The thing that causes some concerns for me is the compression. I tried the old trick of putting my thumb over the spark plug hole, it blew it off making me think I had plenty of compression, but when I tested the compression I only got 30PSI. I don't know what the compression for this engine is supposed to be, but 30psi sounds really low. I then checked the head/cylinder bolts for tightness, they were tight. I did notice with the muffler off a lot of carbon build up around the cylinder port, but didn't seem to be causing an issue. After seeing that, I checked the piston by just looking inside the exhaust port. The piston appears to be scored. I pressed on the ring and its tight, causing me to think the ring is stuck. Does anyone have any other suggestions on what the issue may be here and what the correct compression is supposed to be??? I cant decide to junk it, or tear it apart. I think I may tear it apart then scrap it out..... :help:
 

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If the piston is scored, it needs to be replaced, which probably isn't worth it.:sorry: Also, 30 psi is way too low for any engine. :( The bore is probably worn too.
 

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I doubt that you need another piston for your machine. It sounds like it has either a bad sparkplug or bad crank seals. As long as you or the previous owner did not run the blower for extended use on straight gasoline, you should not need a new piston or set of rings. One other item to check is the shut off switch. Disconnect the wires of the switch and see if that changes anything. A dead of faulty switch could be diverting some of the coils electric charge to ground causing a false start.

Chris
 

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I usually look into the cyl thru the plug hole to check for excessive wall scoring. Also take the muffler off and see what the ring and side of piston look like.
I have found that if the wall is scored too much they will wet the plug excessively when trying to start...even without choke...and not start.
If it has spark and decent compression, it should hit on starting fluid.
Check the crankcase seal/gasket. SOmetimes there is oily sign of leakage.
I had a ryobi backpack blower that would start but not rev up (if I am remembering corrrectly) due to a crankcase gasket leak. It would only rev up if you put your hand over the air output tube...
 

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Discussion Starter · #6 ·
I messed around with this some more. I first put a little bit of oil in the spark plug hole and checked the compression again. With oil in the cylinder the compression went up to 60psi. Then I tried starting it with oil in the cylinder and it started. It ran for a short time and filled the garage with smoke then died, I assuming after it burned the oil up and lost compression again. I tore it all apart thinking the ring was bad. I found the ring was stuck in place and did not move freely. I could see carbon in the groove so I tried scraping it all out to free the ring with no luck. I have it soaking in diesel fuel, not sure if that will work or not. This is my first time tearing down a little 2 stroke engine. I'm assuming the ring is suppose to move freely and flex when its pushed on.....
 

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Discussion Starter · #7 ·
UPDATE: I wasn't able to save the ring. I had to actually pry the ring out of the piston ring groove which caused it to break in several pieces. Cleaned the piston and groove. Couldn't feel any worn or score marks on the piston or piston wall. Replaced the ring and rebuilt the carb. It runs like its brand new. Have less than 12 bucks in parts so I think I'm ahead for now. As for the PSI question I had earlier. After replacing the ring I hooked the compression gauge back up and it read about 55 PSI, before the repair it was showing 30PSI. So these small engines must need 50-60 PSI compression to run. Here's a little extra information. When I checked the spark it was good, when I sprayed starting fluid in the spark plug hole and tried starting, nothing happened not even an attempt to fire. So if you ever have these symptoms check the compression..
 
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