Aeroinjector surging

[polly]

Have just started adjusting the carb, ( #2 needle) with throttle locked the rpm goes from 2500 to 1500 back to 2500 back to 1500 etc. Any help would be appreciated.
Polly

[tonyr]

Hi Polly,

Rather than go into a long winded question and answer session.. perhaps a synopsis of what you have done/not done
wether its inflight or ground run only, cowls on/off, plumbing, gascolator/filter fitted, fuel flow check results and so on?

[polly]

Tried to do three taxi runs, then tied it down for static runs while adjusting the needle. Got no where and decide to buy a 2 1/2 and a 3 needle but they haven't arrived yet. Removed the carb and disassembled. The only thing I've noticed is the play in the needle slide where the adjusting screw ball connects to the slide. Reduced the play.
Replaced the intake manifold connecting hoses even though the old ones looked good. In my way of thinking, air or fuel leaks don't seem to fit. When the needles arrive I'll procede.
Thanks
Polly

[tonyr]

My first thought was a restriction in the fuel flow or a tank vent problem, i.e. partially blocked.

[gammaxy]

I've tried all the needles and don't think I ever had the engine surge like you describe. I suspect your actual problem right now is not the exact taper of the needle. Does adjusting the mixture control when the engine is surging have an effect?

I'd first check that the needle is installed correctly (tapered side up and the end of the taper aligned correctly) and verify that the mixture control arm is at the correct angle when full rich, then verify that the fuel flow rate is ~12-20gph (disconnect the fuel line from the aeroinjector and see how fast you can drain a couple gallons into a bucket).

Does the behavior change when you switch from one ignition to the other?

Do you live near any other Aeroinjector owners who could look at it?