Carburetor adjustment

[flickroll]

Flew my -8 for the first time today

One of few issues is the carb. On the ground I must aggressively lean it to keep the engine from stalling. It was hot today, 95 deg, which exacerbated the problem of too rich. The carb is a MA 4-5, pn 10-3878, s/n 75086013 (float SB NOT done...). Can anyone point me to instructions on how to properly set this carburetor up? Perhaps it's more than a setup problem, perhaps not. For starters, what is a good starting position for the mixture screw? At full power the engine is fine, at reduced power settings it loads up. Thanks

[carguy614]

Jim,
You may want to investigate the float SB. Sounds like the float adjustment may be too high, assuming all else is OK. A sunken float will raise the fuel level in the bowl enough to allow it to run super rich at idle. Next will be fuel spilling from the bowl as the float becomes even lower. Truth is, you will have to do this SB anyway, so now would be the time.

Hope this helps,
Chris

[flickroll]

Good idea. I would like to know a good starting point for the mixture screw. Seems I heard somewhere that it should be 1 1/2 turns out, but eyeballing mine it looks further out than that. Can vibration cause it to back out? I would say however that my engine/prop combination is smooth. Thanks.

[wv4i]

I went to a very well done carb forum put on by Tempest/Volare at Sun N Fun. Unless it' something obvious, and then should comply with all applicable SBs, I would simply have your carb overhauled. A properly equipped overhaul shop can even put it on a flow meter test setup prior to reinstall on engine. You're virtually certain that you have a rich carb situation, and whether it's a stuck float, float with hole in it (essentially stuck), or something else, no matter. Very lean or flooded, equally bad. I would not risk your new airplane.

Meanwhile, congrats on the first flight!!

[pauldan181]

Check for a leaky primer system also. My 8A with a MA4-5 will idle fine even at full rich, I do lean the heck out of it on the ground or eventually it will start fouling the plugs.

To answer your question, my idle mixture screw is at 3 1/2 turns out from seated. If it's richer and i get a lot of popping when fully closing the throttle on final, leaner and I get a slight miss when closing the throttle. I also get a 50 rpm rise at shutdown. I saftied the idle screw there and haven't touched it since.

Paul Danclovic
Jamestown NC

[flickroll]

Aircraft does not have a primer system installed.... I think I may do an overhaul/exchange on the carb which I hope would take care of all service bulletins etc.