First.......put in a new plug. Just because it fires, doesn't mean the plug is good. I have seen engines run (poorly) with a bad plug.
You say it has compression, but does it have enough. Just because the valve seats look good, doesn't mean the are closing all the way. Check the gap, should be approx. .04
A compression gauge is cheap, maybe 15$ and will tell you all you need to know before wasting any time on a junker. I cant give accurate numbers but I will guess and say 130 is new, 110 its at half life and near 80-85 its not going to want to do anything. Try misting in gas with a hand spray bottle just as it starts.
Before ripping it all apart, pour some kerosene or diesel in the sparkplug hole. (bout a quarter cup) Put the plug back in finger tight, without the plug wire attached. Turn the engine over by hand. It will likely not turn all the way because of fluid lock when the piston comes to the top. Leave it sit like that for a day. If a ring is stuck, this may free it, as well as a stuck valve. You can always open a cover on most engines to see the valve stems move. You can always work them up and down with a plyers.
When you want to start it, remove the spark plug and spin it over to blow out the remaining kerosene, clean the plug and reinstall it, and try to start the engine.
Once you get it started, change the oil because the kerosene may have diluted it.
If the kerosene is gone after one day, you definately have a leaking piston ring.
The valve clearance. Over time the valve seats wear and the gap closes, not allowing the vlave to close completely. If the vlave clearance is less than .04, the valves MUST be removed and ground down to the proper clearance.
When I took a small engine course, we learned that the intake valve clearance is .010 and the exhaust is .020 inches. That from memory, and it's been a lot of years since then.
How much time does it take to clean a carb, versus how long to eat potmetal? As I suggested, rinse well and dry. As someone else suggested, rinse promptly, and thoroughly. People (like you) who abuse exclaimation points can be helped!!!!!!
far off. Some idiots need to stop embarassing themselves with clueless flames.
Now you're saying you were right comparing a spark gap with a valve clearance gap...and you're NOT the idiot here!!!!!!!!!! You have waaaay too much time here giving bad advice that you can't keep straight in your head (age related).
Yeah, I'll check them. Visually they look good (i.e. seating evenly and no other obvious major drama has occurred) but that's no guarantee that they're not worn so much as to be inefficient.
I've found the allowed clearances for that engine - 0.005 to 0.007" on the intake and 0.009 to 0.011" on the exhaust.
Yeah, I'll give that a go; as it's a horizontal cylinder I'll have to pull the engine, or just stand the whole mower up on its butt :-) It seems like a worthwhile test, though - I really don't like how loose that piston is feeling compared to the "new" 11HP engine I got.
Just for the record, 0.030" for this B+S engine according to their operating manual (just in case someone stumbles across this thread at a later date! :-)
Hmm, well it fails that test (or passes it, depending on how you look at it. I can keep my thumb there while it's turning over; I can feel it compressing, but it's not so much that I can't keep my thumb in place.
I've only worked with big multi-cylinder engines before, so messing with the small single-cylinder stuff is a bit of a (fun!) learning experience
- I'm not sure how good compression *should* be on such a small engine, but it sounds like this engine doesn't exactly have a lot :-)
(unfortunately I do have a compression tester, but it's 4000 miles away, which isn't much use right now! Maybe I should just cave and buy another one...)
The small engines I've serviced. I've had to pull a rectangular cover from the side of the motor, which exposes the valve springs. The clearance is measured between the end of the valve stem, and the push rod. Have to turn the crank shaft so the lifting pressure is released. As the engine warms up, the valve stems lengthen due to temperature. So, there needs to be a gap, to compensate for the lengthening.
OK, now sitting there with a gas/oil mixture (about 75% gas, 25% oil) in the bore - I'll see how that goes if I leave it overnight.
I checked the valve clearances - 0.005" on the inlet and 0.011" on the exhaust, so those are within spec.
I got the 11HP engine running earlier, borrowing the magneto and spark plug from the broken 10HP. That seems to rule those out as culprits on the 10HP. I still can't definitely rule out carb issues, although it's interesting that the 11HP ran with its carb, but that carb didn't get the
10HP going.
I've not checked the ignition timing yet as I didn't have a suitable wrench for the 1-1/4" bolt on the flywheel, but I suppose I can always compare the flywheel position on the 10HP at TDC relative to the 11HP.
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