Hello All,

I took my Giles 202 to the field today. The engine is a Brison 3.2 with electronic ignition. During the initial ground run engine performance was normal (perhaps slightly rich).

Shortly after take off the engine started to burble, and not develope full power.... it sounded like it was way too rich. I returned for landing without undue delay.

I'm familiar the proper technique of adjusting the High and Low needle valves on Walbro carburated engines. The Brison manual states that as a general starting point the Low should be out between 1.5 - 2.5 turns, and the High needles valves should be out between 5/8th and 1 full turn. However with these settings the engine will idle OK, but when I adjust the throttle beyond 1/2 the engine runs extremely rough, and BACKFIRES! (yikes!).

Here is a list of what I've done to try and problem solve....

1. Replace the fuel with completely fresh fuel. No change in performance.
2. Ensured that the ignition battery has a fresh charge... no change in performance.
3. Cleaned the carburator.... no evidence of debris found... no change in performance.
4. Checked the sparkplug connections.... re-tightend, .... no change in performance.
5. Replaced the sparkplug.... no change in performance.
6. Observed the fuel line for bubbles... no air entering the fuel line noted.
7. Adjusted the low and then the high speed needle valves till I'm blue in the face.... even with progressively lean or progressively rich settings the engine performance seems unchanged (i.e. still backfires beyond 1/2 throttle).

The engine has not been in any accidents at all.

What is going on here? I can't understand why it runs really rough and backfires beyond 1/2 throttle.

Help please.[&o]

Cheers,

Marcus