Lawn Mower - No Power

Missy M · #1 07/24/10, 07:41 AM

I have a riding mower with a Briggs and Strat motor on it. We've rebuilt the carb. New battery. Now it runs, but when you engage the mower or the transmission there is no power. The mower can barely keep running. I'm suspecting it's time for a valve job.

Any other ideas would be appreciated. Thanks.

Wis Bang 2 · #2 07/24/10, 12:30 PM

A burned valve will do that...

Bret4207 · #3 07/25/10, 08:59 AM

So will a flywheel key that partially sheared, throws the timing off. Clogged air filter or fuel filter, bad plugs, or a bad bearing(s) in the mower can all rob power. Blocked exhaust too.

Missy M · #4 07/26/10, 12:29 PM

What about the coil going bad. Weak spark?

Bret4207 · #5 07/27/10, 11:51 AM

Weak spark can be a bad pug wire, bad plug, the coil not being well grounded. Most Briggs I've seen use the flywheel coils. The air gap can cause week spark and so can corrosion on the magnets.

Txrider · #6 07/27/10, 04:40 PM

Could just be as simple as the governor not hooked back up right and adjusted after carb work was done.

Missy M · #7 07/31/10, 07:35 AM

I cleaned the magnet and the contacts, they were rusty. I put spark plug lube on it - it prevents moisture from rusting it. I'm just not sure if I have the correct gap between the magnet and the coil.

agmantoo · #8 07/31/10, 08:13 AM

Is there a fuel filter in the gas line? If so change it before proceeding. Have you tried to adjust the gas on the carb with the engine loaded?

Bearfootfarm · #9 07/31/10, 09:31 AM

Quote:

I'm just not sure if I have the correct gap between the magnet and the coil.

A matchbook cover is just about perfect for setting the gap.

HermitJohn · #10 07/31/10, 11:01 AM

Quote:

Originally Posted by Missy M

What about the coil going bad. Weak spark?

If it starts easy enough, I wouldnt suspect ignition. Though I would replace spark plug on general principles. Not uncommon to even get bad new plug since manufacturers now are chasing last nickel of profit and manufacturing them in Timbuktu or someplace. And check plug gap, that could affect power.

Otherwise I would suspect fuel problems. Since you rebuilt carb, check filter and line. Some mowers run line in through grommet at top of fuel tank and then line is weighted and sits immersed in gasoline inside tank. With the alcohol in fuel anymore this line can disintegrate either collapsing or developing air leaks. This will kill power since your engine isnt getting the gas it requires. Replace with alcohol resistant line. Your mower manufacturer may have a kit with new grommet, line, fitting, etc. But you can buy bulk line. Its the yellow translucent stuff, cant think of common brand name off top of my head. There are other alcohol resistant lines.

BRYAN · #11 08/01/10, 05:22 PM

If the engine runs fine until loaded then slows down smoothly, no missing or backfireing, I would suspect that you have insufficient valve stem clearence. A valve job would fix it.