jagan

I seem to have a low rpm surge which only occurs under 2000 rpm. Upper rpm and full throttle the car runs very strong. I have a BB with a quadrajet and running about 13 degrees of timing. Can't figure this on out.

BB72

Well, believe it or not it could be just play in your suspension. I had a bad front pinion bushing and play in the splines and u-joints that caused my surging. Check all bushings , trailing arms, diff crossmember etc...

jcurrie

I have a similar condition but I know that it is caused by the timing advance. I have disconnected the vacuum advance and am running mechanical only. The springs that I have in there are too stiff - I need to change to lighter ones. Because they are too stiff the car goes through a surge feel as I accelerate until the springs are overcome and advance is in. This occurs in the 1500 to 2300 rpm range. This could be a similar problem with yours. Have you replaced the mechanical or checked into the operation of your vacuum advance?

BigBlockk

It sounds like something has changed and leaned out the transition circuit in the carburetor. You may want to check for vacuum leaks. This would include the vacuum advance canister on the distributer.

BigBlockk

Later.....

66L36Coupe

Couple more things to put on the list to check:

Pull each plug and clean and re-gap or replace. Also inspect your plug wires. Try running your car in the dark and look for arcing ignition wires.

If you run out of ideas, be sure to check for broken valve springs. These will often cause a miss at or around 1500 rpm (especially on big blocks) that is impossible to diagnose until you find them. Happened to me!

DaveP52462

Check for a intake leak.

Dave...

jagan

thanks, I will try some of those ideas. This car has about 100 miles on a TOTAL restoration so the suspension is not the problem. I will look at advance mechanism first.

capevettes

For a low RPM/partiial throttle surge or miss I would check the following:

1.Timing
2. Spark plugs (gap), and wires
3. Fuel filter/possible obstruction under partial throttle that clears with wide open throttle
4. Lean condition/carb.

Good luck

mandingo214

Bringing back an older post, but I am having a similar problem.

I just replaced the distributor on my '74 454, MT, with an HEI unit, and put in new wires and plugs (gapped to .035). From information on other posts, the timing is now set at 36 degrees at 3000rpm, 56 degrees total advance. Idles nice at about 800rpm (about 20 degrees advance), and with the vacuum gauge on the carb base, it draws 6 inches with the carb plates closed (at idle), and a very steady 20 inches with the plates open.

My problem is when cruising along in any gear between 2000-2500rpm I get little surge feelings, like the car wants to accelerate then not. I guess it could be the suspension, but it behaves the same regardless of road condition and mph.

The carb is a replacement Holley.

Any ideas?

baxsom

could be lean surge,

mandingo214

I just read your 11/08 on lean surge (so I could figure out what it meant), but you never posted what fixed it. Was it new jets? One of the guys talks about new squirters? Is that a reference to the accelerator pump?

Thanks.

Rich's'78

You are describing what I think is lean surge, but I am not familiar with Holleys. I suggest you repost with "Holley Lean Surge" and someone will be able to advise you.

On a Q-Jet, the APT is a very sensitive mechanism to cure that.