Bonneville America Forums Forums Off Topic Discussion Forums Lounge Lawn Tractor HELP!!

Ok got a B&S 18H OHV model 31 on my lawn tractor...
It ran fine then I shut it off...now it won't start...It turns over and will occasionaly backfire (both thru the carb and exhaust)...

This is what I have done todate...
Checked Spark...it was there (but replaced the Magnito anyway)
New spark plug(s)Bought 2 just incase...
Carb striped down and cleaned...
Valves adjusted...
ALL Safety's disabled (just incase of some odd short)
Checked Compression (although my gauge seems to be disfunctional) my thumb felt suction and apparently compresion...(it's only spec'd at about 8 lbs)and the fule shot out when I turned it ove sans plug...

it just turns and turns and turns till I kill the battery...recharge it and start the trouble shooting again...

(BTW the flywheel key IS in the proper place and not missing or broken)

The whole thing has me ready to ignite it!

Get a Flymo ...

Well, if you got spark and compression, and you are sure the flywheel key is good (sometimes it can have a hairline crack that you can't see until you pull it out) then the only thing left is air/fuel. First thing I'd do is clean/replace the air filter. I've had many small engines do exactly what you describe (ran fine.. then can't start), and 9 out of 10 times it was a clogged air filter. While you are at it and have the air filter removed, give it a little spritz of starter fluid and see if that kicks her over. If it does and she keeps running, then that was your problem. If she runs for a second and dies, then the problem is somewhere in your fuel delivery.. check/replace filter and check hoses for cracked/crimped/broken spots. If you have a fuel pump, disconnect carb and crank it over a few times to make sure you have gas coming out of the line. There isn't much to them little engines, and you have already ruled out much of what it could be.

Cheers,
Brad

Forgot to mention...changed fule filter, replaced fule lines, Pulled air filter OFF sprayed carb cleaner into EVERYTHING...sprayed starter fluid...all did NADA, nill, jackshit...

the compression is the only thing I'm not entirely certain of...but I am certain that the valves are not frozen and do move up and down...

there is a fule solinoid...but I would have thought that if the fule was the issue the starter fliud would have solved that....

If it's a late model MTD built tractor, they often have some weird @ss safety that goes back through the ignition switch. I had to replace 2 ignition switches in two years on my Craftsman. The last time I waxed it up, painted the rust spots, and stuck it to the first $1200 that came my way.
I do believe that tractor was built by the MGB GT design team.

I have pulled the magnito ground off so the safety switches should be inoperative...shouldnt they?

Any rough running before it crapped out, or when it last ran it was hunky-dory & now nothing? Jeez, with everything you did to diagnose it that's a puzzler.

If it is the latter then my best guess would be something electrical, but, you checked the plug & there was spark when you cranked the motor, correct?

Wish I knew. When they started wiring the GD things like Apollo 1, (with my apologies to the crew) making them work right went over my head.

As I was not the last to use it (Brad, my Son, was) He did'n mention any rough running but then again he's 14 so he remembers the cheat codes to the latest Vid games but alas not this detail...however the Last time I used it it was fine...and Yes there is a clear spark upon cranking...

Pretty soon the local "small engine guy" is gonna find diagnosing it easy...Mr Johnson, I think the 12 lb sledge jambed in the engine case could be preventing your tractor from starting....

Bulk ether +



= happy ending

A video of the process would be much appreciated

If you can wait 'til the rally, we can give it
a right proper sacrifice to the lawn mower Gods.
I do believe it's begging for a ballistics survival test as well.
Maybe start out with some NATO rounds an make her suffer for a while, then work up to the kill.

I once had a spark plug wire that was intermittent drive me crazy for several hours. When I'd hold it out to test it everything was fine, when I put it back on the plug the spark was weak or non-existent. Turned out to be a loose connection or a dirty contact, I'm not sure which because I cleaned and tightened it and it worked fine after that. There's only spark, fuel and air so if it's not one it has the be another.

I sure wish I could tell ya what's wrong with that puppy Rob, but I CAN say that Bucky's "MGB GT and Apollo 1" and your "12lb sledge" lines are sure crackin' me up here!!!

(good luck, and maybe Larry's suggestion might pan out as the culprit)

Ok I just cranked the battery dead again...dumped COPIUOS amounts of ether into the carb....sput, fart, cough, wheeze...pretty flames out of the carb...loud bangs from the exhaust...MORE pretty fire from the carb...(BTW when you remove the dipstick tube, to check the wires going from the stator...and you DON"T put it back before cranking the engine over...you can PAINT much of your garage wall

plug wire is part of the brand new (un-needed magnito...I should have just set the cash on fire it would have been as well spent!) all of the contacts are good cripes I even sanded the rust off of all if the fly wheel (a pointless and useless excersize as the magnet is un effected buy rust) and conections...and all I got was a early July 4th fireworks display

FLUCKIN TRACKTOR must be wired by LUCAS!!! I KNEW i should have put a flippin GREMLIN bell on it!!!

ARRRRRRRRRRRRRRRRRRRRRRRRRGGGGGGGGGGGGGGGGGGGGGGGGGG!!!!!!!!!!!!!!!

OK as a SIDE note...The NH RALLY will have a HAY BALEING workshop added to the itinerary!

Good cause I haven't even started mowing a hay field this year. Sounds like the timing is off (not that I know how to correct that).

Timing on Briggs is set by the key on the flywheel (which is in place and whole).........................

See this is why my lawnmowers come from the dump, I have low exceptions and life time warranty for 100% of the purchase price.

If you take it to the small engine repair place it will almost certainly be something that will make you feel stupid for not having thought if it yourself. That's why I always have my excuses ready ahead of time.

Did you yank the muffler off? A loose spark suppressor can really create havoc...

Ok, so you have ruled out fuel/air, spark and timing. Based on the backfire through the carb, it does sound like a timing problem, but you say the key is in place and fine. About the only other thing that would cause those symptoms is valves. Have you checked and/or adjusted your valves? Is this a single or dual cylinder engine and how are the valves operated (chain/belt/gear driven)?

Cheers,
Brad

Breaks and Scrap iron made some faulty engines:
Depending what year you have they used a flawed key that is prone to shear. I went through this on my mom's mower. A local shop fixed it for me by machining the small side (crank or flywheel, can't remember what one) Every time the mower hit a rock it sheared the key before they fixed it. I put 3 keys in it before they did that, been fine ever since. The old key was kind of T shaped the new one is like a square bar like most.

backfiring out both ends? Check the valve timing. I had a '54 Hudson do that and I had to change the timing chain.

timing key or broken crank. my $.02

Ok I pulled the motor and cracked the case....cam shaft is OK, crank is OK, timing marks are dead on...

Havent pulled the head ....yet....but as I don't have a head gasket for it....yet....I'm reluctant to do so....

Pull the head, it's not running anyway.
Hole in piston or rings fubar. Possibly valve(s).

I have a MTD tractor with the same B&S engine with the same problem. I replaced everything I thought I should replace to get it to fire. nothing worked.
It now has 2 flat tires from sitting for a year. You've taken the diagnostics to the next level.
If you ever get it running, please post your solution. Mine was buying a $150 push mower

Believe it or not, mine will do that if you bypass the safety switchs, for some reason they have to be operating or it will not start.

possible automatic compression release stuck....

What is this "automatic compression release" of which you speak??

All briggs engines of modern overhead cam design in the horsepower you speak of have an auto compression release. Works off the valves. Valves being out of adjustment can cause it to not function properly. But since you said you adjusted the valves, I would tend to think maybe its stuck open...

Here's a link to a fairly knowledgeable fellow on the subject.http://www.smalleng.com/

Is it time for the plasma cutter yet?

OK!!!
I know not WHY...yet...BUT

I cracked the head off...AND...the exhaust valve is not seated all the way...there has to be at least 1/32 or so of daylight shining thru the seat....

Also as an interesting note...I found H2O in the cylinder....could have happened while I was blasting heaps of oil soaked grass and dust prior to benching it!