Engine Surging

[Viggen90]

I have a slant six 67 Barracuda. About four months ago I put on Clifford headers and intake, a Weber two barrel, and dual exhaust through Magnaflow XL's. Right away I noticed that the car will run fine to about 55-60 mph where it dies out and begins to surge. If I back off the surging will stop and I can usually get up to highway speed. It's obviously running rich because when I get on it there's a ton of unburned gas coming out the tailpipe. I called Clifford and they recommended that I replace the distributor. I put in a new Mallory distributor which resolved the issue a but it's still there. The hot weather also seems to be making it worse. Is this just an issue I can resolve by getting the car on a dyno and doing some more tuning or is there something more serious?

 

[Bulldozer]

It's obviously running rich because when I get on it there's a ton of unburned gas coming out the tailpipe.

uummm ...

that's most likely your answer

its probably dumping gas because the float is stuck, dirt or garbage in the needle/seat OR the float is sunk

take the carb apart and clean it, set the float level again
is it running on all 6 cylinders? sometimes a surge is caused buy a stretched/jumped timing chain

 

[Darter6]

Wow., Sounds like over rich condition on one hand and a fuel delivery problem on another.A dyno session sure can't hurt.Other things to think about is the condition of fuel tank and everything from there to the carb.I've had this happen on 3 different cars. 1- crud/rust in tank,2-a rag in the gas tank,3- the fuel screen or "sock" that is at the end of the pickup came apart and got hung up in the fuel line bends.
This is just a starting point.

 

[Viggen90]

Fuel delivery was my first thought so I put in an electric fuel pump because the mechanical one was pretty shot. I also put in a new gas tank last month because the old one was leaking. Didn't notice a big difference with either replacement.

Could it still be the carb even though it's brand new? I've pretty much left the carb alone other than tuning because I figured it should be good straight out of the box.

It's running on all six cylinders and has no issues at idle. After I push through the surging and get up to about 70 mph it usually runs fine.

 

[My*65*Dart]

How did you run your exhaust? Did you run it into one off the headers and then split it or did you run right off each header (3&3) all the way back? Just curious. (pictures would be cool!).

 

[Bulldozer]

Fuel delivery was my first thought so I put in an electric fuel pump because the mechanical one was pretty shot. I also put in a new gas tank last month because the old one was leaking. Didn't notice a big difference with either replacement.

Could it still be the carb even though it's brand new? I've pretty much left the carb alone other than tuning because I figured it should be good straight out of the box.

It's running on all six cylinders and has no issues at idle. After I push through the surging and get up to about 70 mph it usually runs fine.

those carbs only need 3 -4 psi of fuel pressure. if you don't have a regulator , you may be pushing 5-7 psi of fuel right past the needle and forcing gas into it . what electric pump do you have?. I would try a new original replacement mechanical fuel pump OR regulate what you have at 3 - 4 psi and see if that cures it. and yes its possible there is crap holding the needle valve open or that the float is stuck. you can also try tapping on the float bowl.

 

[Viggen90]

I have a regulator on there and it's indicating about 3 psi. I hadn't thought of the float or needle valve. Thanks

 

[Viggen90]

How did you run your exhaust? Did you run it into one off the headers and then split it or did you run right off each header (3&3) all the way back? Just curious. (pictures would be cool!).

The exhaust is right off each header all the way back. I put an x-pipe in which seems to equalize out the sound. I'll try to get some pictures for you.