engine spits and backfires at full throttle

A

ACF

Well-Known Member
have a briggs engine model 33r877-0007-g1 starts up runs great at low speed but when the throttle is increased it spits and backfires via carb and muffler.
i have changed the carb and the coil did not resolve the issue, valve clearance checked and reset as needed, saw no issues with flywheel key.
the camshaft was replaced a couple of months ago ran great no problems.
the engine does every now and does have excessive pressure.
so looking to see what could be the problem to this engine, is there a chance that the camshaft is not lined up correctly.

thanks
AC
 
ACF said:
have a briggs engine model 33r877-0007-g1 starts up runs great at low speed but when the throttle is increased it spits and backfires via carb and muffler.
i have changed the carb and the coil did not resolve the issue, valve clearance checked and reset as needed, saw no issues with flywheel key.
the camshaft was replaced a couple of months ago ran great no problems.
the engine does every now and does have excessive pressure.
so looking to see what could be the problem to this engine, is there a chance that the camshaft is not lined up correctly.

thanks
AC
Click to expand...
You do have a timing mark on cam that needs to line up. Would not know if that is correct unless you open up the engine case.

Most likely you have carburetor issue as long as everything else checks out. Thoroughly clean OEM carburetor and reinstall. Make sure intake gaskets are good.
 
ACF said:
starts up runs great at low speed but when the throttle is increased it spits and backfires via carb and muffler.
Click to expand...
Super lean in my book. Main jet wants more fuel. Classic lack of proper air/fuel mix.

Wait carb AND muffler? At the same time?

Check flywheel key.
 
What rider or zero turn is this engine on?

Fuel tank and line restriction is the number one problem I find with most that have had multiple "bolt on" parts replaced.

Blow compressed air back through the fuel supply line coming up to the engine and see if the problem goes away. If so, the tank needs to be pulled out and cleaned. It would be wise to also replace the fuel lines because debris gets lodged in them also and it can be impossible to clear all the stuff out.

Most people never clean the fuel tank because they are hard to access, but that is how I get many of them to run like new again.
 
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