mark.bitterlich(at)navy.m
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 Posted: Mon Sep 26, 2016 7:43 am Post subject: [Non-DoD Source] Re: Re: M14P running very rich at idle, st |
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It might be wise to take a look at the FUEL PRESSURE indicator in the aircraft with the engine running and the boost pump on and then off and record the readings.
If the fuel pressure is close to identical with the electric fuel pump on and the engine running that adds information on whether having it running is suspect to the cause of the overly rich condition at idle. If the pressure goes to the high limit or over with the pump on, it is highly suspect as the cause. Of course the other easy thing to do is just to try it and see what happens, but when you do, still take the time to look at the fuel pressure gage as that is critical.
FYI, I have a Weldon electric fuel pump in series with a Lycoming GSO-480B1J6 and with both the Weldon pump and the mechanical one running, the fuel pressure pegs to the right and the engine runs slightly rich. A high fuel pressure is not uncommon on aircraft that have been modified with an aftermarket electric fuel pump. What a pressure carb does when the fuel pressure is too high is going to differ slightly from one carb to the next due to the fact that if the pressure is actually above limits a lot of things come into play as to what exactly will happen. For example, on my Bendix pressure carb, it ran very rich with both pumps turning. I then had the Bendix rebuilt (for other reasons), and it STOPPED running rich with both pumps on! The repair center deduced I had a worn poppet valve and that was the reason that happened. In any case, the Russian carb is a pressure carb as well, so it is hard to say. Bottom line, check the fuel pressure!
The "Kimball Mod" has no bearing on the condition you are presently seeing. That mod was done mostly to "PF" engines to help with a stumble when advancing the throttle quickly. He deduced that the engine was getting too much fuel from the "accelerator" pump circuit and he just blocked it off. This mod was presented at a time when the Russian carb was not fully understood. Since then what in truth was going on has been deduced and the method to correct it properly found. There are jets in the carb, that actually control air flow which allows you to adjust this aspect of engine operation properly. I am sure both Richard Goode and George Coy have these jets in stock, but again, it will not impact rich idle.
So number 1, check fuel pressure. Following that, remember that the manual pump could be bad and allowing excess fuel to get into the circuit. If neither of those are bad, it is time to try and adjust the idle circuit on the carb.
I defer to those more expert than myself, at least two of which have been speaking to the matter.
Mark
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