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Good evening. I have a B&S 120000 series vertical shaft, OHV engine that won't start when hot. I've tried all the tips I could find with no success. I've cleaned the carb, replaced the rings and head gasket (no ridge on the cylinder), set valves to .006, replaced the coil, tested the flywheel magnetism, ck carb spacers and replaced the plug. It has fresh gas and clean air filter. I'm not sure where to go from here. Any help would be greatly appreciated!

Have you tried taking the gas cap off?

Yes. Also made sure it was venting properly. Unfortunately everything was good.

Try spraying some starting fluid thru carb or a little fuel, does it try to start?

This is sometimes an indication of carb float needle leaking a little flooding the engine. I would turn off gas a few seconds before stopping the engine and see if that helps. No gas line shutoff, clamp the gas line. Test above should help indicate if my suggestion might be good. Fixing an engine by helter skelter replacing parts is not very economical, might as well buy new engine.

Walt Conner

Actually the engine was given to me by a friend because it wouldn't run. I could hear blow-by from a head gasket. I popped the head and the head gasket was blown. Since the head was off I did the valves. A lot of carbon so I thought I'd check the piston. The bore was good but the rings were partially stuck. Replaced,re-assembled and tested. The spark was weak so I replaced the coil, good spark. But I do have the hot start problem. It doesn't matter if the gas is shut off or not. I checked he compression and it's the same hot or cold. I think next I better replace the carb to head gaskets although they look good.

Ya I've got a 12M902 coming in that's doing the same thing (hard to start hot)

I don't really care for that model:thumbdown:

will let ya know if I find anything with it.

lugnut

Mikel1 said:

Try spraying some starting fluid thru carb or a little fuel, does it try to start?

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So did you try this?

lugnut1 said:

Ya I've got a 12M902 coming in that's doing the same thing (hard to start hot)

I don't really care for that model:thumbdown:

will let ya know if I find anything with it.

lugnut

Click to expand...

Great! let me know if you find anything. One thing I did was put a fan blowing on the carb. I'm thinking that that leads me back to carb isolators. Going to give that a try.

Mikel1 said:

So did you try this?

Click to expand...

Yes, both gas and starting fluid, not a pop.

vincent52100 said:

Yes, both gas and starting fluid, not a pop.

Click to expand...

Both of your posts above re-enforces my suggestion for shutting off the gas.

Walt Conner

Tinkerer200 said:

Both of your posts above re-enforces my suggestion for shutting off the gas.

Walt Conner

Click to expand...

Right, did shut of the gas. Same result

According to the single cylinder manual ohv for model 120000 vertical series, valve specs are intake- .003-.005 in. and exhaust- .005-.007in.

FAQ: How to Clean an Engine | Briggs & Stratton Engines read through this concerning engine overheating, just keep scrolling down page.

CURED!! As I said. I put a fan blowing on the carb area and within 20 minutes it started right up. That led me to believe that the problem was caused by heat transferring from the head to the carb. I had a piece of heat resistant plastic about 1/4" thick and used it to fabricate a spacer for the carb. Ran a full tank of gas through it, fillled it, and it started on the second pull. Technical explanation "Then a Miracle Occurred"