Briggs/Stratton 3.5 hp

[Puddin' Man]

Briggs/Stratton 3.5 hp

'allo,

Over 1 year ago, somebody gave me an old MTD 20" mower with a B&S 3.5 hp. Ran rough, so I cleaned the carb, changed oil, plug, etc. Ran fine, better'n my newer Quantum 4hp. I garaged it as a backup mower.

About a year later, after no further use, it won't start. Carb looks fine. Evidently no spark. Tough to properly test: only one of me, not enough hands. Pulled the plug, wired the safety bar, pulled engine cover. Trying to test just turning the flywheel by hand. Even put a multimeter (@ 500v ac) on it: just barely, barely moved.

I'd just pitch the unit if I had conclusive evidence that the magneto (or whatever) was defective. But I've had 3.5's before and never had a problem with spark (except plug replacement).

Anybody gotta inkling why such 3.5 would run fine 1 year ago, fail to gen spark now?

Thx, Puddin'

Pease pudding hot, Pease pudding cold, Pease pudding in the pot Nine days old.

[David Martel]

Puddin,

That the carb looks fine isn't definitive. Get some starting fluid, spray it into the carb throat, and see if it will start. When you store an engine for a long time either run it dry or use a gas stabilizer.

Dave M.

[Bob F]

To test the spark, pull the plug, push it back into the plug wire, and prop or wire the base of the plug to the engine metal. Then try to start it. The spark should be evident. If it is, you probably have a carb problem.

Bob

[Stormin Mormon]

Wait till dark night time. Screw the plug out. snap the plug back into the end of the plug wire. Pull safety handle down, and then yank the rip cord. With no plug, there is no compression, so the motor spins fine. Look at the gap of the plug to see if you see spark. Easier to see in the dark night time.

The other guy is right, try a squirt of ether on the air filter (not into the spark hole). See if it runs on ether.

Turning by hand probably not fast enough to fire the magneto.

[terry]

. My 3.5 B and S mower is acting the same. It was running rough and surging, so had changed the plug; put in a new carburetor kit and checked the magneto clearance under the flywheel and it ran fine for a couple of weeks of occasional use. Then it stopped. Haven't bothered since cos end of season. Howver someone reminded me to check the the safety off switch; when I let go of the safety bar (a sort of deadman's lever on the handle which must be held down to start and run) a switch operated by a cable from the lever kills the ignition circuit. So just a suggestion if the OP has a mower with a 'safety stop' lever

[Bob F]

A squirt of gas into the air intake works fine also.

Bob

[Puddin' Man]

Pardone, mssr, but that requires (at least) 3 (very long) arms/hands. I have only 2. :-)

'Tis a test that I've run many times. If spark gen is functional, I've had no trouble seeing it in the daytime.

May be some out the garage ...

You may be right bout thatun.

Thanks, P

Pease pudding hot, Pease pudding cold, Pease pudding in the pot Nine days old.

[Puddin' Man]

All I ever needed. I had pulled the air filter. Watched while working the bulb which squirted gas into the carb throat. Damned well know it was getting gas.

Thx, P

Pease pudding hot, Pease pudding cold, Pease pudding in the pot Nine days old.

[Puddin' Man]

Y'all were both right.

It's wierd. I work the primer bulb, can see gas shooting into the throat of the carb. But it won't start.

Shoot some ether in it and it fires. Then dies.

Guess I gotta dissemble the catb again ...

Muchas Gracias, Puddin'

Pease pudding hot, Pease pudding cold, Pease pudding in the pot Nine days old.

[Stormin Mormon]

Ah, but the events happen at different times.