Hey everyone... I have been lurking here while I was looking for my next project. Well I finally found it... A '76 F350 crew cab. It's was a one owner truck, 58,000 miles (complete maint. records came with the truck), and has a 460 with the C6. It is in pretty good shape but needs some work as it has sat for the past 5 years or so. It was running pretty good and I drove it home but the accelerator pump was not working and I found alot of vacuum leaks when I got it home and started looking around under the hood.

Anyway, I decided to rebuild the original 4350 carb (not the best but hope to do for now) so I picked up a carb kit, dismantled it, cleaned it up, and replaced all the parts and gaskets. All the passage ways are now clear and the accellerator pump works shooting fuel down both sides of the carb.

Here are my problems...
The carb has a small fuel leak between the two halves. The gasket is new and the screws are tight so I think the float is not set right or is stuck (could have jammed it upon reassembly) which is causing the bowl to overfill as it seams like to me the fuel should not get that high anyway. I will take the top off and check it again.

The other problem is that when trying to start it (before I noticed the fuel leak), it was backfiring through the carb (lots of fire). I did not touch anything else so I don't think it is the timing which could be off but it should not be any worse than it was before. I was able to get it to run for a few seconds (poorly) but it stalled out then backfired again when trying to restart it

My question is would a carb over filling cause backfires like this? I am going to take it apart tomorrow and double check everything again but just want to know if I will be chasing another problem. I did replace all the vacuum lines and plug off the ones not in use so there should not be any more vacuum leaks.

Thanks for your help and sorry if the answer should be painfully obvious..

 

Typically, the only time a carburetor causes backfiring is if you try to start the motor cold with the choke open. Since you didn't change anything related to timing since it was last running well, the aforementioned case is a very likely cause of your problem.

If the fuel bowl is overfilling, it's very likely the float is set incorrectly. I assume by "halves" you mean the throttle body and air horn (top piece), in which case you're correct that the fuel level should not reach the gasket surface.

 

Now that you mention it, I was trying to start the engine cold (-12c here) with the choke open. I didn't know that could cause it to backfire. I'm sure the over fuelling isn't helping either.

And yes, I am taking about the gasket between the fuel bowl and air horn.
Thanks for your help... hopefully I have it all resolved tomorrow.