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2-Cycle Motor question

Is 55psi high enough compression for a 2-cycle lawn mower motor (4hp made by Fuji, ported, no reed valves)? What should the compression be?

little more info - Bought a Snapper push lawn mower with a 4hp 2-cycle motor that does not start. Label says "Manufactured by Fuji Corp of Japan". No reed valve, just ported. I can see spark. I spray starter fluid in carb and cannot get it to fire. With the choke off, I noticed that the starter fluid will puff out of the carb. One puff per rev. I removed the muffler and no difference with the puff through the carb and do feel puff at muffler. Checked compression and get 55psi. I checked a chain saw once that ran fine and I thought it made 75psi, so thought 55 may be ok. Any suggestions and interpretations of what I have observed would be appreciated.

Thanks, Bobby

Reply to
bobby
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Check the woodruff key holding the flywheel to the crank.

I've seen mowers with plenty of spark, plenty of fluel, no go, and a key broken from running into things.

Thomas

Reply to
Thomas Tornblom

Thomas, Thanks for the suggestion. I hadn't thought of that and will check. I kind of doubt this is the problem as I belive the previous owner said it was running when he parked it last year. I have an email in to him also trying to confirm.

Thanks, bb

Reply to
bobby

Maybe he parked it on a rock....

I was going to suggest the same thing.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
Reply to
Mike Romain

that engine is a wisconsin-robin, made by teledyne, bought by fuji, bought by subaru i think. 55psi is low. pull the carb and muffler and check for piston scuffing and or suck rings. it does have a compression release port on the exhaust side so it won't give a real accurate comp. reading. just because you have spark doesn't mean it's at the right time. is that a blade clutch model?? they had a bad time with BBC flywheels coming apart and shearing the timing keys. Chip

Reply to
Chip Stein

Chip, Thanks for the info. I pulled the head and saw a hole above the exhaust port. Was wondering what it was but sounds like it could be the compression release port. The cylinder walls looked good but didn't look any farther. Looking through the carb and exhaust ports, it doesn't look scuffed, but I will probably see if I can get a ring and gasket kit for it anyway.

It does not have the blade clutch, but based on all of the replies I have gotten, I will pull the flywheel and check the key. I didn't have a lot of time to mess with it, but I did see metal shavings stuck to the magnets in the flywheel. Was curious what was dragging and causing this anyway. I didn't hear any scraping when pulling the rope, but maybe this is related to the problem.

The previous owner did reply and said it ran great the last time he ran it (Sept of last year). Started easy start and no problem.

Thanks to all who replied! bb

Reply to
bobby

no bbc, then it's a zone start model. they were good for allowing spark but not releasing the brake puck on the flywheel. it's time to pull the blower housing and see what's going on. Chip

Reply to
Chip Stein

no bbc, then it's a zone start model. they were good for allowing spark but not releasing the brake puck on the flywheel. it's time to pull the blower housing and see what's going on. Chip

Reply to
Chip Stein

no bbc, then it's a zone start model. they were good for allowing spark but not releasing the brake puck on the flywheel. it's time to pull the blower housing and see what's going on. Chip

Reply to
Chip Stein

Chip,

Many thanks for the input. I checked timing with a light and spark hits just before TDC, so I still don't think flywheel key is broken. I have the cover off but didn't notice the brake puck (forgot they have these), but I did think it was harder to pull the rope than it should be. even with the plug out, there is drag. I was going to take belts off to see of the drive mechanism was causing, but you probably just hit it. Where is the brake puck. Does it contact the outer rim of the flywheel or is it under the flywheel? As I said, I have the cover off exposing the flywheel (needed to see it to check timing) and didn't notice a puck dragging against the outer edge of the flywheel, but wasn't looking for it.

Again, many thanks as I think you just gave me the answer.

Bobby

Reply to
bobby

maybe the flywheel ket is sheared, like the briggs do. that means the spark is there but not at the correct time? also the crankcase seals may be tired. the compression DOES seem low, too. good luck, sammmm

Reply to
sammmm

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