Fuel Selector Valve and "Diesel Effect"

[faselh]

My fuel selector valve does not shut off the fuel flow when in the vertical up position.
I noticed this when I tried to shut off the engine for soaring after a long climb to about 13000 feet (very hot day). The engine kept running ("diesel effect") even with both mags off. Therefore I tried to starve the engine by turning off the fuel flow. To my surprise it kept running (with mags off) and developed full power when the throttle was opened completely. So I cancelled the soaring plans.

After landing, I checked if I could starve the engine by shutting off the fuel selector valve but the engine kept running (with both carbs on). After about 5 minutes I gave up, and then tried to shut the engine down by turning off the mags. To my relief, the engine stopped immediately. I had already feared sitting in the plane for a long time and waiting until the engine would finally stop running.

I have 3 questions:
1) Did anybody experience this "diesel effect"?
2) Did anybody have a problem with a defective fuel selector valve?
3) With the fuel selector valve in the off position, how long can the engine run in your plane (due to the fuel already in the carbs and the fuel lines)?

Thanks,
Hermann

[Holliday Obrecht]

Hi Hermann,

I too had problems with my fuel selector valve a while back. When I had it selected to the right tank, it would feed off the left tank and vice versa. This was a real "head scratcher" and made fuel management in flight quite a guessing game!! When we removed the whole blue anodized fuel selector valve and took it apart, we found a set of white nylon "cups" that fit around a metal ball that has holes drilled in it to direct fuel flow. The nylon cups act as seals to seal off fuel flow when you turn the fuel selector in the cockpit. The right and left cups are threaded and had vibrated out so they no longer made a leak proof seal up against the metal ball. On close examination, the fit is quite sloppy--the cup's diameter or threads need to be machined slightly larger so they fit snugger and do not back off with vibration. I have a feeling the third white cup that seals the "off" position for the fuel selector has probably backed off and does not seal off the fuel. Therefore, some fuel is always sneaking by, which is enough to keep the engine running. I wrote several emails to Eng. Casthillo alerting him to this deficiency in my ship, but never got a response. I feel these nylon cup seals need to be re-engineered so they fit snugger.

[faselh]

Holliday,
thanks for the information. I will try to open up the selector and see what is going on.
Hermann