2007 Briggs 17 1/2 hp lawn tractor Runs then starts jerking then quits.

flattire

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#1
Starts easily, runs smooth except sounds like engine is spitting(?) every 2 seconds. Cuts perfectly then starts hopping or jerking and will stop in 2 minutes. After sitting overnight same thing over again. New plug, cleaned air filter and replaced filter pre cleaner. No change. Any suggestions will be appreciated. Thanks
 

billr

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#2
I don't know if I can help any, but the first step is to post the engine model number so I can look at what it is. That number will be on the block or flywheel-cover.
 

billr

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#5
When it stops, will it start back up and go through the "run two minutes and stop" routine; or do you have to let it sit for a while? If so, how long? If it won't re-start right away, check for spark and try a quick blast of starting-fluid. Let's try to determine if this is a fuel or ignition problem.

Unfortunately, I think that engine has a compression-release (called "Easy-Spin"?); so doing a meaningful compression test may be impossible. I think I see that mechanism on the camshaft in an IPB, but there just isn't enough detail/clarity to be sure.

Looking for an IPB, I find two B&S models that are close to what you posted. They have the same P/N for replacement engine or short-block; so must be essentially the same to each other. They are:
31G777-0806-B1 and 31G777-0806-E1

If it won't re-start right away, another thing to check is the valve clearances. Check well into the power stroke (~90 ATDC) as that compression release holds the exhaust valve open at times you wouldn't normally expect!
 

billr

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#6
Another thing to try:

Disconnect the "kill" wire to the magneto, the wire that gets grounded by a switch on the throttle linkage. Those switches are about as crude as possible and can act erratic. I had one beat me up badly a while back before I caught on!
 

flattire

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Started right up and got about 50 feet from the house. Started the leaping and hopping and died. Hooked up the spark tester and got strong spark. After 10 seconds it started and the engine did the jumping thing back to the house and died. Checked spark and spark is strong. I did put a new inline round fuel filter on when i put a new plug in the other day. Waited 20 minutes started right up,ran smooth for 5 min. then began cutting out and revving up again every second or 2. This time i didn;t take it out of the carport to test. Same results. I think cutting out and reving back up better describes the way it does.
 

billr

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#8
Try running it with the gas cap loose or off. Let's eliminate the possibility of a plugged vent on that.
 

flattire

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#9
I believe you got it Bill. I took the cap off and the vent hole was covered up solid. Cleaned it with a small wire , fired up the mower and let it run at pretty fast rpm's for 55 minutes. runs great. Just got in from mowing 20 minutes or so , all good. Will give it a good workout tomorrow evening. I like your method of troubleshooting, eliminating one possibility at a time and solving the problem. My telling you thanks doesn't seem like enough but I sure appreciate your staying with me until I can now use my L/T. Maybe someday i can return the favor. Bill (aka flattire)