J

jeff beckley

Well Known Member
Today my 0-360 started running rough. Backfiring while at cruse. I landed to check things out. Upon restarting my engine was flooded and I had a heck of a time getting it going. Once started and cleaned out I proceeded to do a run up and noticed that I could not produce full power until i pulled the mixture back 2/3 of the way. I could not get it to idle with the mixture in all the way. The only way to get it started now is to have the mixture half way out and then lean it 2/3 of the way just to keep it running. I can produce full power at that setting.

Another note I noticed that the fuel pressure continue to rise even after shutting down the engine and fuel pump. This could be from high heat in the engine compartment.

I have checked the linkages and proper operation of the mixture control system. OK

Carb is a MA4-5 with the f mod for the RV7A.

Could i possibly be looking at a stuck needle/float valve?

After it cooled a bit everything ran better. Did not have to lean as much.

Any Ideas?
 
Check your float in the carb,I had some friends have this happen while descending enroute to the bahamas,turned out the float had a small hole in it and had filled with fuel and sunk,this nwas on a new engine.Bob in East TN.
 
Rough

Does sound like the float,

A friend who is an A&P/IA has found a few "new and newly rebuilt" MA-4's with the screws loose that hold the top flange of the carb to the bottom bowl. There was space between the parting surfaces even though the safety tabs were bent over. This will make them run rough too. Just another possibility.:D
 
The more i think about it the more i think it has to be one of two things.
A stuck float or a float that is sinking.
With the engine compartment temps being as high as they were and causing a higher than normal fuel pressure the float was being pushed off it's seat.
A couple of times I had some really bad flooding. Lots of black smoke.
I could not get it to run correctly at any mixture setting until the fuel pressure dropped back below 5.5 lbs.
 
High fuel pressure will flood the engine, regardless of float/float valve condition. I had to replace a fuel pump for that reason, even though FIVE A&P's told me it couldn't happen. After replacing all the carb parts and wasting over a month, replacing the FP fixed the problem. Have no idea if this is your problem, but worth considering.

Bob Kelly
 
Float bowl

Check the attachment of the float bowl. The 12/18 screws tend to work lose, the bowl drops down and the engine runs rich.
 
Just an update. Took the carb apart and found a small little peace of crud lodged in the float. I had a new float assembly and installed that. When I did the run up I got an additional 150 rpm static from before:)
I am sure that the high fuel pressures were from high heat conditions inside the cowl. Thanks for the suggestions.
 
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