What fuel fitting attaches to the carb?

ArVeeNiner · #1 04-18-2009, 04:57 PM

I have a MA-4SPA carb. Van's drawing OP-28 says that a AN823-6D fitting gets installed into the carb. That fitting has a pipe thread that goes into the carb and it takes about 3/4 of a turn to get snug.

When I look into the female fitting on the carb, it looks as though there is some sort of flare in there that is made to take a male tube fitting. See the pictures below. My question is, is Van's correct in calling out the AN823-6D?

osxuser · #2 04-18-2009, 05:57 PM

Yes, it's a pipe thread fitting.

DickDe · #3 04-19-2009, 03:57 PM

The fitting you have on the carb. in your picture appears to be anodized aluminum. On the engine most will use steel fittings here as well as on the gascolator. I don't know if that is a requirement but I was told it is accepted good practice because of the added strength and the relatively severe consequences if it fails. I used steel and my Cessna had steel as well.

Dick DeCramer
RV6 N500DD flying
RV8 fuselage
Northfield, MN

osxuser · #4 04-19-2009, 11:34 PM

I concur that steel or brass would be better choices than Aluminum, but it's not unacceptable to use aluminum.

Rick_A · #5 04-20-2009, 06:54 AM

I used steel on most of the fuel and oil fitting FWF. I've got a bunch of aluminum AN fitting that came with the FWF kit that I never used.

Beancounter · #6 04-20-2009, 09:03 AM

The finger screen female fitting on my Marvel carb was NOT national pipe thread. It was straight thread just like the mechanical fuel pump fittings. Please check yours. I dont know how safe it would be to rely on 3/4 of a turn with an NPT fitting in a straight thread.

osxuser · #7 04-20-2009, 10:35 AM

Hmm, how old is your carb? The finger screen itself isn't pipe thread, but usually the inlet side of it is... I've never see one otherwise.

ArVeeNiner · #8 04-20-2009, 01:52 PM

I'm not sure how old the carb is. It was rebuilt a couple of years ago for a guy with a Vari-Eze but never used by him.

I'll go with steel. I was just following Van's drawing but that has bit me on a few occasions during this build.

Honestly, it feels like it's made for a pipe thread. The 3/4 turn I'm referring to is until it gets finger snug. I have yet to put a wrench on it. It threads in quite easily. I wonder how trying to thread a pipe thread into a straight hole would act. Would the end of the pipe thread actually be smaller in diameter than the straight thread diameter?

osxuser · #9 04-22-2009, 09:11 AM

Hmm, If it starts to tighten up really quickly, and you can't get 3-4 full turns in before it becomes really tight (with a wrench), it's possible you don't have a NPT fitting, i've never seen one, but they I guess they exsist (see above). My solution if that was the case would be to buy a new finger screen rather than deal with a straight fitting.