I Just bought a rebuilt carburetor and I am having some problems. It is a motorcraft 2100 and it "looks" like it is a good rebuild. I am putting it on my 1974 F-250 highboy with a 390.
Heres the problem:
It will only start when the accelerator is wide open, then the engine revs higher than I've ever had it before (no tach) and the carburetor has this loud air sucking sound through the top. The air sucking is so loud that I can't even hear the engine over it. It runs for a few seconds and dies, I can't even get it to stay running full open for more than 5-10 seconds.
-The adjustment screws on the bottom front are 2 full turns out from closed.
-All of the vacuum tubes are either hooked up correctly or plugged.
-The engine ran like a champ with the old carb but it was leaking fuel so I got rid of it and can't even put it back on.
-The choke valve is closed almost fully and when I try to open it manually it kills the engine immediately, or the engine just dies as I do it because it won't keep running.
-I checked the float and it is adjusted properly.
-The accelerator pump is working fine, it shoots a stream of fuel into the venturi.
-I adjusted the choke so it would stay open with no change in the results.

I don't have a lot of experience with carbs but the couple I have put on has worked pretty well with only some fine tuning. I have never heard about a carb sucking air the way this one is. If anyone can help I would appreciate it.

Thanks

Tom

 

 

Have you contacted the people you bought the carb from. What do they say.

Are you sure you didn't leave a rag in the intake?

IMO, I think it's starving for fuel. I know it ran fine before the R&R, but now it may not have enough fuel for the new carb.

 

Well, the air sucking sound is just that. It is sucking air into the carb, which will be alot if it is reved up and loud. You need to get your idle down before you can do anything else. I am guessing like the rest of the country it has been cold around there. The engine needs to warm up before it will run without the choke on. Start by turning down your idle, although it will be faster on a cold start. There is a sticker on the drivers side valve cover that if you are lucky, will tell you what the fast and slow idle RPM's should be. to get the truck warmed up, start it any way you can, right before it dies stick a screw drive into top of carb to open choke slightly. Again, can't make any meanigful changes till it is at operating temp.

 

After giving it much thought, I'd have to say you have a vacuum leak, as your already hearing. Take a can of ether and spray around the base of the carb, listen for a rise of rpm, that's where the leak is.

Did it come with a carb spacer?? If so it has to be used and use new gaskets at the intake, and at the carb base.

 

You are correct Johnny. I did in fact have a vacuum leak coming from the spacer. The problem was that I had the carb to spacer gasket and the spacer to intake gasket switched. I took off the carb and stacked up the gaskets and spacer together and found that there was a large gap in between the spacer and intake that the wrong gasket wasn't closing. I swapped them around and it fired up like a champ. Thanks for all of the help guys.

Tom

 

Glad I could help!