I'm having a little trouble with a new carb install. Here are the specifics:

74 L-48 all stock internals
New Edelbrock Performer dual-plane intake
New Holley Street Avenger 670 CFM Vac. Sec. Carb
- Main Jets - 65
- Secondary Jets - 68
- Pump Squirter - 31

The engine runs great in all modes except for "light cruise". While maintaining a speed at over 1200 rpm, there is a little surge feeling. Kind of like the car is nosing over a little. I can give it a little gas and it accelerates smoothly. I can punch it and it takes off hard. When I let it settle down to a constant speed, it is fine for a couple of seconds and then I can feel it start it's little surge again. It's more than a feeling though, I can hear it through the exhaust. It seems to me like it is leaning out but I went up to 67 primary jets and can't tell any difference.

Any ideas would be greatly appreciated.

 

pull a couple of plugs and look and see if they are lean

 

Try opening up on the idle mixture screws a little. 1200rpm is a little low for the mains to be starting up in a Holley. I think it's still running on the idle/off idle circuit.

BigBlockk

Later.....

 

Could be a little bit of flooding as well. If it gets worse over time, I'd look at the float valve. You might try putting a gas treatment through. If it's only a little resin, the cleaner might fix it.

 

Since the original post, I richened it up again. I went up to 69 jets on the primaries. I couldn't tell that that made any difference in the surge feeling. Since I have gone up 4 jet sizes, I decided that it had to be something else. This is a bone stock L-48 after all. It couldn't need that much fuel. I decided to check the timing. It is dead on.

The mechancial advance is coming in at about 2200 rpm. Then I checked the vacuum advance. It's working but this is where I have a question. I ran the car up to between 2500 and 3000 rpm (about where it is when cruising at 65 or 70 mph. The port on the carb has full vacuum at the port on the metering block above the idle mixture screw on the right side (where I had the advance hooked in). Is that correct????

Should the vacuum advance be at full advance while at 70 mph???

I ran the car on the interstate this morning with the vacuum advance disconnected and the surge is significantly decreased and may even be gone.

So my question is: Where should I connect the vacuum advance to the carb if not in the location that the instructions to the carb stated?

 

You beat me to it, I was going to suggest too much timing....Try using manifold vacuum, and make sure your total at 3000 rpm isn't much higher than 52*. You may want to try an adjustable vacuum advance canister.

 

manifold vac.

 

Update:

Still having problems with this one. I have tried several things on this with no positive results. Below are the different steps I've tried:

I had previously jetted the carb up twice. I jetted it back down to the original 65 jet size. I held this constant while doing timing adjustments.

I moved the vacuum feed for the vacuum advance from the primary metering block to direct manifold vacuum. This made it idle a little better but didn't affect the surge at light cruise.

I unplugged the vacuum advance altogether (upon Holley tech's advice) and advanced the timing. This didn't help the surge at all and the overall drivability suffered.

I then decided to exagerate the changes I was making to the timing to see if this was timing related at all. I advanced the timing to the point that it was hard to crank. That didn't help the surge. I retarded it to about 2 degrees initial and that didn't help either. While I thought this may be timing related, I am now not convinced. This distributor/vacuum advance was running perfectly before the carb/intake swap. Didn't have any of these surging problems.

Since I have gone up on the jetting with no noticible improvement, I'm now going to hold the timing constant and jet down.

Do any of you have any other suggestions as to what could be causing this??? I'm beginning to run out of options here. HELP!!!!!!!!

Also, in an above post, I stated that the surge was significantly decreased by unplugging the vac. advance. That seemed to be the case but on the way home that day, it was still there. When I drove it to work that morning it seemed to be not as bad. Also, it seems to run better in the morning when the air is denser. Would that indicate a rich condition???

Thanks in advance for your input.