I mentioned in an earlier post that the fuel flow with the modified carbuator needle seemed unreliable. Well it also seemed unreliable with the #3 needle.
I discovered two issued contributing to the inconsistane fuel "richness" flow.
First, to my surprise I was down to less than one gallon in the fuel tank. The good news is that the engine was still running a full RPM, but bad news is that it was much leaner than I would have preferred. The operating limitation for this plane states the No Takeoff fuel of 4 gallons.
After adding 10 gallons to the tank I still noticed fuel flow inconsistantly at full throttle. It would start at around 9.8 GPH, then end up around 9.4 GPH. I loosened the fuel tank cap, and to my surprise the fuel flow jumped to 10.2 GPH and stayed there.
I doublechecked the plans, to see where I had gone wrone, but the fuel tank vent tube was the correct size. I made the decision to replace the vent tube with one that has a 50% larger inner diameter.
The larger vent tube did the trick, and now I'm getting consistand fuel flow.
NOTE: Durning this process, I removed the fuel filter element to check for obstructions, but found none. I also re-routed the fuel line so to prevent a high spot between the fuel filter and the carburator
