Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Hi my name is ***** ***** welcome to Just Answer. You have went over everything that would cause this normally. Did it continously backfire through the carb while it was running ?
Ok can you check your oil , does it have a gas smell to it or is it thin ?
Has it been changed since the carburetorreplacement?
Because you have covered alot of bases , the flywheel keyis good , valves are gapped the carburetor has been replaced. Besides a worn cam the other thought that comes to my mind is if the old cab was allowing gas to bypass the valves and into the crankcase and mix with the oil, that would cause backfiring , another is if you have a anti backfire solenoid and it's bad it will backfire when shutting it off
Is this a briggs engine
Ok , the coil was properly gapped right
Ok. This has the plastic type carb right ? , also how old is the gas in it and what grade of gas is it ?
Unless you got a faulty carburetor I'd start to suspect a cam issue or a valve sticking . Those plastic carburetors are known for not being great . You have done everything to a tee that would fiX a common issue . Did it just start backfiring out of the blue and does it stay running or backfire and die
Ok , im will opt out to see if any other techs have any other ideas. You really covered all bases so it has me stumped with being able to see it in person but if it was a cam issue it would do it constantly so I don't think it's that . I will opt out and sorry I couldn't help you resolve the issue
How was the valves checked? Did you have the cylinder head off? Everything points to sticking valve.
Backfire has to be spark occurring , when valve is open, and that is the only way that happens. Unless timing is changing, And with new coil, that is not moving.
But you didn't remove the valves from the head and clean the stems and the guides?
The needle valve passage is fully open, not plugged with debris from old fuel line?