I have a 10hp Sears Tecumseh boat engine. It will run perfectly for about 20 seconds then quits. Whats wrong?

Question

I have checked the carb and it appears to be clean.

Answer 1

Once again, restricted fuel flow.  check all screens and filters.

Answer 2

if you can spray gas into the carb and it attemptd to run then you know it is a fuel problem. you diagnose these things a step at a time.

If you don't feel you have enough knowledge then take it to an outboard  engine mechanic.

Answer 3

I don't know that particular motor, but speaking of 2-stroke carbed outboards in general, 20 seconds is about how long it takes 'em to empty a carb bowl.  Drain the bowl when it quits, just to see if that's the case, if so, try new fuel lines/fittings, still no good rebuild the fuel pump.

Also consider whether it's overheating.

Check the spark plugs right after it dies - could be running rich and flooding out.  Worn float valves can let fuel past into the cylinders.  Fuel pump diaphrams get perforated, leak through the vacuum pulse line into the crankcase.

You can't tell about a carb just by looking.  Lot of tiny passages you can't see into.   Float valve & seat gets sticky, engine starves for fuel.

Have you checked the compression on this motor lately?