O 320 Slight roughness at full rich

[Dfspau2]

I am in the prebuy phase of a 75 Grumman Traveler with hicomp stc

The engine seems to run great other than at full rich. Current owner says that it has been that way for the 4 yrs that he has owned it. I have flown in the plane and leaning very slightly smooths everything out. The day that I flew the airplane it was 90-93 F flying out of 500’MSL. DA ~2500’.

Any ideas?

 

[Tom-D]

When was the carb replaced/rebuilt?
Show us the carb data tag.

 

[Dfspau2]

Carb was rebuilt in the last couple of years. I will try to get the data tag from the current owner

 

[chemgeek]

The original MA-4 carb on the Traveler was subject to a bunch of ADs and SBs over the years relating to the venturi jet (one-piece, two-piece, whatever), float assembly, etc. The plastic float could log with fuel, and the venturi jets were variously bad. Mine always stumbled on throttle acceleration, even with the "latest" version venturi jet. It never ran extra rich, however. First place to start is to see if all the ADs and SBs have been complied with, and then figure out why it's apparently running too rich.

When I overhauled my engine, I got a brand new carb (5009 I think) with yet another "improved" venturi jet, and avoided the casting flaw AD. What a difference. The new carb works like a champ--no stumbles, easy starting.

 

[Tom-D]

The original MA-4 carb on the Traveler was subject to a bunch of ADs and SBs over the years relating to the venturi jet (one-piece, two-piece, whatever), float assembly, etc. The plastic float could log with fuel, and the venturi jets were variously bad. Mine always stumbled on throttle acceleration, even with the "latest" version venturi jet. It never ran extra rich, however. First place to start is to see if all the ADs and SBs have been complied with, and then figure out why it's apparently running too rich.

When I overhauled my engine, I got a brand new carb (5009 I think) with yet another "improved" venturi jet, and avoided the casting flaw AD. What a difference. The new carb works like a champ--no stumbles, easy starting.

Hell of a lot better to buy a rebuilt carb from Kelly.

 

[bluerooster]

IMHO better to "IRAN" the carb. Mabe replace everything except the casting.

 

[Tom-D]

IMHO better to "IRAN" the carb. Mabe replace everything except the casting.

Problem with that is, PARTS, you can't buy the OEM parts, all you can get is Kelly new parts that change the carb in its entirety.

And then if it does not run correctly,, what then?

 

[bluerooster]

What's the difference between me re-building my carb (IRAN) using Kelly parts, and Kelly doing the same with my carb? Other than I know who did the work, and how it was done. I've had issue with Kelly reman in the past, and while they stand behind their product, the downtime can be an issue. After all, it ain't rocket surgery, it's a simple carburettor.

 

[Tom-D]

What's the difference between me re-building my carb (IRAN) using Kelly parts, and Kelly doing the same with my carb? Other than I know who did the work, and how it was done. I've had issue with Kelly reman in the past, and while they stand behind their product, the downtime can be an issue. After all, it ain't rocket surgery, it's a simple carburettor.

You can not rebuild a carb in the field.

how would you test it?

read FAR 43.2 and tell me what "rebuilt" means.

I repair a lot of carbs.

If you were to replace every part in the carb, I'd wager it will run rich.

 

[bluerooster]

Yes you can re-build a carb in the field. IRAN. Inspect, and repair as necessary. Just suppose, upon inspection, that it's necessary to replace everything except the casting. It's still a repair. And when properly done, it won't run rich, or lean. Of course, if you are not comfortable doing carb work, then by all means send it out for repair.