dead B+S mower engine

[Jules Richardson]

(does this count as "home", or is there a better place for it?)

I think today's the last chance for getting our elderly MTD lawn tractor running before I throw in the towel and go buy a (long-overdue) replacement tomorrow. It's refused to start after being set aside for the cold season, and the grass has got to that point where it needs the first cut of the year (as soon as this wet spell ends sometime next week, anyway)

The engine's a 10HP B+S with electric start. Fresh gas, fresh oil. Fuel line's clear, carb is free of debris. It's got compression, spark, and is getting gas to the cylinder. I pulled the head and checked the bore and valve seats, and no obvious problems there.

I've got the service manual, and the best it's managing at the moment is with the needle valve 1-1/2 turns out and idle valve at 1 turn out (as per manual for "this'll at least allow it to run so you can adjust the carb"), where it'll *almost* run - it'll fire and turn fast enough to disengage the starter pinion, then immediately die on me.

Any ideas what else to look at? I wondered about timing, but it seems unlikely that's out unless the cam gear jumped a tooth. I could pull the engine and take the bottom cover off to take a look (and check the governor mechanism*), but it's something of a last resort job after I've checked everything else.

• I don't think it's that, as I've tried manually holding the throttle wide open at the carb, overriding what the governor might be trying to do, and it doesn't help.

cheers

Jules

[salty]

If it ran when you parked it for the winter, and it doesn't run now, then it is almost a 100% certainty that your carb is not as clean as you think. It needs to be disassembled, soaked in proper carb cleaner, and all the passages blown clear with compressed air.

Then start over with a dry, clean, gas tank and lines. Fill with gas that you bought within the past month.

[dpb]

Jules Richardson wrote: ...

Does it have a fuel filter? What position is the choke plate in; is it functioning correctly?

How did it run last year? You say it's old, is the carb body worn badly at the throttle plate shaft holes so the air mixture is fouled up badly--that's a typical failure mechanism with age. It tends to make them run w/ a noticeable surge as the air:fuel mixture varies widely as a symptom from last year did it have such behavior?

As another posted, perhaps there is some small sediment impeding the carb or the float is stuck or similar problem. Does it seem starved or rich for fuel-related symptoms?

What shape is the plug? What about the plug wire; is it in good condition or could it be cracked from age?

Oh, so many choices... :)

--

[Jeff The Drunk]

Spray some starting fluid in the carb then crank. If it runs for a few seconds after then you have a carb problem - plugged main jet orifice or clogged bowl valve.

[jamesgangnc]

I agree with some of the others.

Have you cranked it with the plug out and connected? Do this in the shade. Remove the plug, Hook it back to the plug wire. Lay it on the cylinder head or block somewhere where it is grounded. Crank it. You see sparks? If not you have an ignition issue.

With it all assembled remove the air cleaner. Spray a little starter fluid into the carb while cranking it. If it fires and tries to run but then dies you have a gas delivery issue. Disconnect the fuel line and see if gas runs out all over the place. If it doesn;t then blow into the line and if that causes gas to start running out you have crud in your tank. If the gas line is not clogged then you have carb problem.

If you have spark and it won't even try to start while spraying starter fluid into it then check the shear pin under the flywheel.

[Stormin Mormon]

See if it will run for a second or two on ether, sprayed onto the air filter. Warning.... do not spray ether directly into the air intake. Double definitely not into the spark plug hole. (That's how my Dad's generator got killed.) If so, you've got carb problems.

Other thing to do, is to remove the carb, and put some Permatex #2 non hardening on both sides of the gasket. They dry out, and then the engine sucks air through the gasket, instead of drawing gas mix.

[hallerb]

try removing spark plug, insert some gasoline, reinstall plug and try to start.

if it runs for a short time its no doubt a clogged carb or fuel line issue. this might get it running fine, the engines vacuum may clear the carb problem

[hibb]

If you are getting gas, spark and compression, the thing should run. The things I would look at first is if it is getting enough gas and spark. You could try dumping a little gas in the carb and cranking it over to see if it will start or at least try to start. If it runs at least a little bit, then take a closer look at the gas delivery system.

If it doesn't start or at least try to fire up, take out the plug and see if it is soaking wet. If it is real wet with gas, dry it out and try again. If it doesn't fire at all, then take a closer look at the ignition system. You may be getting spark but not enough to fire the gas.

Also, if you are long overdue to replace this thing and don't get much satisfaction out of getting an old machine to run and can afford a new one. Go for it.

David

[The Daring Dufas]

When I was a kid, I discovered that a lawnmower engine would run on Liquid Wrench. Of course there are carb cleaners that a motor will run on while cleaning things. I've had luck with spray cleaners that have the extension tube using it to blow open the tiny ports in the carb.

TDD

[Jeff The Drunk]

When I was a young lad I found out a horizontal shaft Kohler engine would run on propane from the unlit nozzle of a propane torch held in the carb venturi. Also found out the motor could easily over-rev and bust the connecting rod if you fed it too much propane. :)

[The Daring Dufas]

Someone comes to me for a job and tells me they have a lot of experience. I ask them: "How much equipment have you burned up?" If they answer none, I tell them: "You obviously have no experience, I need someone who has already burned up thousands of dollars in equipment because I can't afford it. A learning experience can be very expensive."

TDD

[Jules Richardson]

Yes and yes - good flow through the filter, and choke plate closes correctly.

Very much so. I was always surprised it ran at all :-) It always was a bit picky about starting - I got the knack of tickling the throttle just- so. The carb is certainly worn, particularly around those shaft holes for the throttle plate, so I'm under no illusion that it's not the best of carbs :-) I'm just not sure what's changed since it was run last, though

- whatever carb faults it had shouldn't have grown worse by just sitting there.

It always ran rich (and there was quite a lot of fouling within the head when I pulled it).

No *visible* cracks, tip is in good condition (and I checked the gap). If I pull the plug and ground it, then turn the engine over, it's giving a healthy-looking spark, although I suppose there's the possibility that what looks good isn't good enough.

Yep! It's the figuring out what's changed while it's just sat there which is probably key, I suppose.

cheers

Jules

[Jules Richardson]

Yeah, I think that's where I'm at - visually, it appears to be doing all the things it needs to be doing, but there must be something (e.g. igntion or fuel delivery) that it's not doing well enough - unless some major drama has occurred in the valve or ignition timing (yuck!).

Oh, I love getting old stuff going again :-) Problem with this mower is that it's on extended loan, rather than mine, so I get reluctant to pour money into spares (and there's a big list of stuff on it that's pretty much worn out and can't be "fixed" other than by replacing parts).

If it belonged to me I'd strip it all down and fix everything (I could spend a couple of hundred on parts, I bet, but that's still cheaper than a new one) and doubtless give it a fresh coat of paint too ;-) But as it'll probably go back to its owner one day, maybe it's just time to invest in a replacement.

cheers

Jules

[Jules Richardson]

Hmm, I'll revisit that. I can pull it and strip it down in less than 5 minutes these days :-) Don't think I have any carb cleaner, although I do have some brake parts cleaner - maybe that's asking for trouble, though! (I'm not sure how similar it is)

Yeah, the gas lines/filter are another possibility I suppose - as I said, it seems to get good flow from the tank, but I've heard of rubber hoses essentially delaminating and collapsing internally when they age. As a test I suppose I can ensure a clean tank and try without a filter (I think I have some spare new hose somewhere of the right size)

cheers

Jules

[ransley]

It runs just not under load right, ive had several 4 motors like that and it was electrical. One a bad wire, two the ignition module, one the coil. A motors spark at idle needs not be strong to run, but to ignite alot of gas for load it needs to be strong. That doesnt rule out low compression or a carburator-fuel issue but since it runs it could be electrical. Is the spark small and weak and maybe red in color, but ive had small blue sparks not enought to go past idle. Sears sells a 4$ induction tester you just touch the wire while its running, if the spark is what dies as you load it you should be able to see it, and squirting gas in the carb with throttle open should help rule out or confirm a fuel issue. Why did you pull the head?

[dpb]

Jules Richardson wrote: ...

Close enough; anything highly solvent that evaporates cleanly will do...

...

These small engines if the hose flows it's not the problem. If there is a filter (many don't, that is a possibility--the w/o it test is easy to eliminate the possibility of course).

--

[hibb]

Yeah, I've got an old Alis Chalmers Rotary Tiller that I am debating on whether to fix or not. I had not used it in a couple of decades and my nephew took it a few years ago to try to get it going. When I got it back, it is missing the gas tank and air cleaner and I am thinking I just might as well replace the carburetor. I checked on line and the gas tank is about $70, the air cleaner is about $35 and the carb would be around $130.

That's about a third of the cost of a new one but If I get this thing going and take better care of it and use it more, I bet it would last me for as long as I am able to use it.

David

[Jon Danniken]

Buy a NEW spark plug before you do anything else.

Jon

[The Black Knight]

[snip]

Is there a fuel shut-off solenoid inside the carb?

It sounds like you are getting fuel to the carb, just not through the carb.

Sticky float plunger, clogged passages, or partially functioning fuel solenoid are the usual culprits.

B&S engines have fixed timing.

A partially shorn shaft key might goof up the timing a bit, but the engine should still run if it fires at all. It's an all or nothing kind of thing.

Concentrate on the carb.

[Oren]

Also check the gap before install. Those plugs gapped at the factory are not always accurate... Get the correct heat range for the plug as they are not all the same :)

OP - loosen the gas cap a turn or two. If the cap vent is clogged the tank will create a vacuum, affecting fuel flow. Clean vent with a paper clip.

You have plenty of oil in the engine, right. If the motor has a low oil kill switch that would shut the down engine.