Great info on the carbs, thanks a bunch. I have been adjusting the mixture on model engines for a number of years but I have an OS 60 FP with an air bleed carb that has me temporarly stumped. This is an engine that was installed in a model that I bought used. It doesn't appear to have a lot of time on it and has excellent compression and runs very strong on the top end and with a 12X4 APC will pull a 4 lb. 12 oz. model straight up till it is out of sight. I adjust the HSN about 300 RPM below peak but if I pull the throttle back to 50% it immediately load up and eventually dies. The only way to get it to lean out again is to pinch off the fuel line. While the throttle is at 50% it is blowing fuel out the exhaust and will empty a full tank in just a couple of minutes.

Here is the deal.<ul>[*]The tank with all new plumbing is installed with the tank outlet on the same line with the HSN.[*]Tried two different brands of 15% fuel.[*]Tried 2 new glow plugs with different heat ranges with no change.[*]Disassembled and cleaned the carb with no change.[*]Checked the low speed air bleed hole by sticking a small allen wrench the same size through the hole and it is not clogged.[*]Adjusted the servo throw and throttle stop adjustment for max open and close.[*]Adjusted the LSN so that the air bleed is completely uncovered. Even completely removed the LSN and put it in my pocket, no change.[/list]The next thing that I am going to try is to drill out the air bleed so it is a little bit larger. If that doesn't fix it I guess I will have to spring for a carb with a fuel adjustment on the LSN.

To my thinking, any air leaks around the backplate, carb seat or HSN assembly would cause it to run lean, not rich.

Any clues?