Backfireing

[lr172]

I would start in the carb, as fuel issues (either too rich or too lean) are most likely to cause this collection of symptom. This assumes that you are starting up a cold engine, warming for a brief time then taking off. My first guess would be an issue with the float or needle/seat attached to it. When problems arise here, it can overfill (too rich) or underfill (too lean) the carb bowl. Both can induce conditions that will present to the novice as an inability to smoothly make high power and apparent backfires. It could also be am misbehaving fuel pump. Clearly it is an issue in which heat is changing something and that something is causing the problem. However, in your scenario, most of the parts have not reached that high of a temperature within 10 minutes.

Larry

[rmarshall234]

Maybe the third time will be the charm...

One comes out the air filter and the other out the tailpipe

[lr172]

Originally Posted by rmarshall234

Maybe the third time will be the charm...

One comes out the air filter and the other out the tailpipe

Yes, we can keep telling the OP that (or maybe it was directed at me), but it is hard for a novice to understand the nuances of each of these and discern the difference in sound. The OP was sitting in the cockpit, so how would he know which orifice that the explosion came from? Best we just give him diagnostic aids based upon the likelihood of both. Excluding start up events, backfires at medium to high power settings (where the OP's symptoms begin) are uncommon without serious issues with the valve train or serious issues with ignition timing, so we can assume these were afterfires, as it starts and runs fine for 10 minutes before the issue reappears.

And yes, I know that the over rich or lean will cause afterfires, not backfires. But I am using the terminology that the OP understands. The vast majority of people call these backfires and as diagnosticians, have to work within the operators knowledge level.

[Avanza]

I would check fuel filter/ gascolator for dirt and water.
Remove fuel hose from carburator and run the starter for 10 s.
Check that there is fuel flow from the pump.
Run engine on LEFT magneto/ electronic ignition only. 700-2.000 rpm.
Run engine on RIGHT magneto/ electronic ignition only. 700- 2.000 rpm.
Don´t fly the aircraft before problem is resolved.

https://msacarbs.com/carburetor-troubleshooting/

Telephone 336-446-0002; FAX 336-446-0007;
or Email: customerservice@msacarbs.com

Good luck

[mahlon_r]

Make sure the engine breather is clear and unobstructed.
Good Luck,
Mahlon

[RV7A Flyer]

You're wasting your breath. Another drive-by posting.