Briggs Will not Accelerate

[dunoon2]

Briggs 311777-070-E1, idles fine but, when you increase throttle fast backfires thru carb and dies, when you go slow speeds up OK but, dies under load. Cleaned carb, checked timing, checked valve clearance, replaced plug, no luck. Any suggestions? Thanks

Rich Davis
3-M's
Mobile Mower Maintenance

[KE4AVB]

First I would check for partially sheared flywheel key and would do a leakdown test...These engines are known for head gasket failures especially between the cylinder and valve gallley.

[bgsengine]

I think you need to clean the carb again , better this time around unless you cleaned it TOO good and resized the main nozzle.. or the float is too high.

Both cases - sudden WOT acceleration, and under load, the fuel is fed through the main nozzle of the carburetor which , if not cleaned enough, will be too lean. leading to misfiring and backfires - or too rich, which would mean there's more fuel vapor still burning when the intake valve opens - Also check for a restricted exhaust / muffler

When you ease the RPMs up, governor control maintains throttle position , which, when not loaded, generally feeds most of the fuel the engine needs through the *IDLE* circuit. (Which is why in some industries, notably diesel - they call top no load RPM as "High Idle" )

[dunoon2]

I replaced the carb with one I had lying around here after I cleaned it. It done the same thing.

[bobodu]

Wouldn't be surprised that a carb you had lying around is just as bad......

[Deere2me]

I replaced the carb with one I had lying around here after I cleaned it. It done the same thing.

Could be what our esteemed sandbox monitor said........ peruse this:http://outdoorpowerinfo.com/repairs/briggs_intek_single_ohv_nikki_carb.asp

You said you checked the timing.....please...elaborate.

As an aside..have you checked for air leaks ? Warped manifold ? Spray the joints with carb spray while idling, if it speeds up ya got a leak, right?