232 6 cylinder intake backfire

[Just Empty Every Pocket]

I recently purchased a 1977 CJ 5 with a blown engine. I rebuilt engine.
The engine was already removed so I,m not sure if anything is missing. but to my problem. The fuel lines where plugged when I first tried to start engine. I removed tank cleaned and rodded out fuel lines. I replaced filter after a few runs.

I have had an intake back fire problem from the beginning. The engine runs great in shop at all rpms. If engine cold, while driving it would backfire thru carb. If engine at temp, it would run with intermittent problems. I tried to adjust fuel mixture and the screw was frozen. I also found that the top plate of carb had stripped screws. I replaced carb with a rebuilt one. Now it does not matter if it is at temp or cold it backfires thru carb while driving. Still runs fine in shop at all rpms, just not under load.

I have bypassed fuel filter and return line temporarly, in an effort to see if carb was starving with no change in operation. I moved vacuum advance to a different vac port, no change. The intake vacuum at idle is 18 inches.

The service manual suggested several things that I believe I have ruled out.
I am thinking maybe the intake gasket to block may be leaking due to the need to warm engine before. But why it it doing it regardless of temp. with new carb?

At a loss what to try next. Replace intake gaskets? Replace fuel pump? Could I have damaged the fuel pump while trying start up with plugged lines?

 

[SteelHeadz]

The issue your having with your Jeep sounds like a Timing issue or Fuel. Have you tried to rebuild you carburator and see if the Needles are straight and not gummed up. Make sure that all the little holes and ports on the throat of the carburator is clean.Adjust the carburator floats as needed. Make sure your base gasket has no tears .Check all the Vacuum lines and replace them as needed.A vacuum leak will normally cause a high idle but sometimes a minute leak is insignificant at idle but can cause a significant change with with a throttle input. This in turn will give you a high volume of Air Vs. Fuel. If you have moved the Vac. Advance supply hose from one port to another and there was no change, I would suspect that the distributor mechanical advance is not doing it's job.. When you set the Ignition timing, make sure that the vacuum advance is disconnected and all the vacuum ports thats not being used is plugged. If the fuel system has a return line, that shouldn't damage the fuel pump. Check for a proper fuel pressure as well. 18Hg of vacuum is not bad at idle and should get close to zero with a quick wide open throttle. When you re-install your carburator, Screw the Air/Fuel mixture screw all the way in then back it out at least 1 turn and a 1/2 to 2 turns. Adjust the Choke plate properly. Welcome to Jeepz.com

 

[TerryMason]

Welcome to Jeepz.com Joe!

I've moved this thread to the CJ forum, where you'll get more help.

 

[Just Empty Every Pocket]

Thanks for the reply. I have tried all the above. I checked fuel pump and all sources of vacuum leaks. I checked timing and mechanical and vac advance. All seemed to be working.
I reinstalled the original carb and returned to the original problem of intake backfire when cold.
The original carb is an altitude adjustable carter yf-1 carb. The rebuilt carb is a carter yf-1 without the altitude adjustment. I have called the carb rebuider to see what needs to be done to make this change.
Shouldn't I be able to change to a regular carb since I live and use it in and around Dallas Texas? Are the intake manifolds different between alititude and non altitude models?
I know the timing and idle are different, but the service manual doesn't say any difference in the manifold.
Thanks again for your replies. All help and suggestions are appriciated!

 

[SteelHeadz]

Thanks for the reply. I have tried all the above. I checked fuel pump and all sources of vacuum leaks. I checked timing and mechanical and vac advance. All seemed to be working.
I reinstalled the original carb and returned to the original problem of intake backfire when cold.
The original carb is an altitude adjustable carter yf-1 carb. The rebuilt carb is a carter yf-1 without the altitude adjustment. I have called the carb rebuider to see what needs to be done to make this change.
Shouldn't I be able to change to a regular carb since I live and use it in and around Dallas Texas? Are the intake manifolds different between alititude and non altitude models?
I know the timing and idle are different, but the service manual doesn't say any difference in the manifold.
Thanks again for your replies. All help and suggestions are appriciated!

You can try that thoery by driving up here to Kerrville but i doubt that altitude is the issue. Did you double check the choke adjustment?.