dead B+S mower engine

[Jules Richardson]

No... I'm not sure who made the carb, unless B+S rolled their own. It's a pretty simple beast really.

Well, *something* is getting through because I can pull the carb off and it's wet on the 'engine side' of the carb body. I wonder that's actually a sign of the problem, though, and it's just not atomizing the fuel properly and is getting neat gas pouring into the cylinder rather than a nice mist (the presence of just enough vapor might explain the way it tries to cough into life once sometimes, then promptly dies).

OTOH, maybe I'm clutching at straws ;-)

Oh, other possible symptom: the carb's getting a *lot* of gas; it drips quite a lot from the intake side if I have the air filter assembly off (the bolt that holds the filter on runs right through the carb body on the intake). It's possible it's always been like that, and that's normal behavior, but it surprised me there'd be that much gas "upstream" of the choke plate.

Possible, I suppose. I checked that the float isn't holed, and the metering needle there looks good and seems to seat well (the carb sits slightly lower than the tank, so if there were a float problem I think I'd get gas pouring out everywhere even with the mower just sitting).

I can't completely rule that out, as there are a couple of passages I can't really get to (access sealed at the factory), although I can blow through them, so I know they're not completely blocked.

I might try to pull the flywheel (which times the ignition) just to check that - it'd be a heck of a coinicidence if it just happened right at shut- down last season, but stranger things have happened :-) I've certainly had keys shear on smaller engines before.

Yeah, I just pulled it again and double-checked what I could. I ended up dumping a little neat brake cleaner into the inlet "upstream" of the float and throttle, and the engine actually turned about four revs under its own power before dying (it'd only do about 1 or 2 revs by itself on gas). I can't decide if that's indicative of anything meaningful or not :-)

cheers

Jules

[Jules Richardson]

No, not running at all. I've had it run maybe a couple of revs under its own power a few times, then it dies on me (it doesn't seem consistent though - if it fires like that, I can leave the throttle in exactly the same spot and come back to it a few minutes later, and it won't fire at all)

Just to take a look at the valve seats & cylinder bore - only takes a couple of minutes, and I wanted to make sure the valves looked like they were seating properly and the bore wasn't trashed for whatever reason. All appeared OK, though.

cheers

Jules

[Oren]

If you do pull the flywheel, shine the magnets (two) with some emory cloth. Clean any contacts and shine them.

I've seen surface rust (humid areas) on the flywheel magnets - enough to diminish the good clean firing of the ignition.

[The Daring Dufas]

Something I've noticed on engines like yours is the need for valve clearance adjustment after the engine has rub for a number of years. I've worked on a lot of standby generators and the overhead valve engines are easy to adjust the valves on. The valve in head engines such as the one I believe you have is a different story. I had one that would only run if I preheated it with a propane torch which caused the metal to expand enough to let the valves seal. Here is a video that explains a lot about dong a valve job on a L head engine.

TDD

[clare]

Check your local lawn mower "bone yard" for a carb that hasn't got the bushings all worn out of it and start over with it.

[clare]

NOT EMERY CLOTH. Some of the emery is magnetic. Use Alox paper (Aluminum Oxide)

[Stormin Mormon]

Now, that sounds like the voice of experience. I knew a kid one time who ran an ungoverned lawn mower to get to town and back. A couple times, until it over revved, and broke.

We recently had a thread about getting home on paint thinner, when the gas tank was near empty. I've heard gas engines run well on a spray of WD-40.

[Stormin Mormon]

Yes, better to kill a few things before they hire on with you.

[Stormin Mormon]

Easy off oven cleaner is excellent for cleaning carbs. Strips off gum and varnish. Rinse well, and dry before reassembling. Best carb cleaner I've ever used.

[Stormin Mormon]

Champion had a run of bad CJ-8 for a few years. That's a brand I avoid.

During start, the throttle is wide open, and the choke closed.

[Stormin Mormon]

The mowers I've serviced. if the valve clearance is too low, the mower runs 15 minutes, fades out, and died. Restarts after it's cold. I learned that in a small engine repair course. One guy a couple streets over was going nuts on a mower repair, and turned out valve clearance was the problem.

[ransley]

If compression is to low it wont start easily or at all, you need a

15$ tester to find out the real pressure. Leaking fuel to me means flooding, is plug wet after you try.

[clare]

Because the propellant is basically Propane - which gets the kerosene lit. Bulg WD40 won't light worth crap.

[clare]

Just don't forget to rinse promptly. - and thoroughly. On a zinc carb it's not as bad as on aluminum.

[Stormin Mormon]

Didn't know that about the propellant. I've never tried bulg WD40.

[Stormin Mormon]

Yes, promptly is good. Within seconds of spraying the oven cleaner. metals damage due to the strong alkalai, is a very real possibility.

[Jules Richardson]

Yes - watch this space... I brought home an almost-identical mower yesterday, except that it's got the 7-speed transmission and an 11HP B+S engine (rather than my 5-speed / 10HP). I think the carb's identical though - I suspect most of the engine is, and it's just a different bore/ stroke.

Actually, the 'new' mower's possibly a better long-term candidate than the current one. For 15 years of standing out in the open it's pretty solid. Front axle and tires are shot, and there's something up with the deck, but those would swap over easily enough.

I think I'll use engine parts from it to get my current one going (I can last about one more week before mowing), but after that screw around with it some and see if I can get it up and running.

cheers

Jules

[Jules Richardson]

Yep - I was just ruling out a governor problem by manually holding the throttle (just in case the governor was screwed and trying to throttle things way back before the engine had chance to cough into life)

[Jules Richardson]

I'm wondering about the compression, now. Can low compression result in an engine that won't even start/run under no load?

It's got some compression for sure (nice healthy hiss from the crankcase breather on the down-stroke if I turn by hand), but I tore into the 11HP engine from the donor mower I picked up at the weekend, and that engine's piston fits *far* more snugly in the bore than on the 10HP. It slides well (so no apparent issue with ears of it sitting there unusued), but fits better with no detectable side-to-side movement if I try wobbling it, unlike the 10HP.

(Although if it is a compression issue, I still don't get why it was running last season and magically broke over the winter...)

Oh, I cleaned up the carb on the 11HP and tried it on the 10HP. It will fire consistantly for maybe 4-5revs, then die, so not really any better than the 10HP's own carb was. No different swapping the plug, either. Magneto is unfortunately trashed on the 11HP, so I can't try swapping that.

cheers

Jules

[dpb]

Jules Richardson wrote: ...

Certainly, but it has to be pretty doggone low to not run at all...

If you can use a thumb in the spark plug hole and keep it from blowing by, it's a good chance it is that bad...

--