lag on acceleration
 

My 76 L-48 has a noticable lag when accelerating, then will take off and go. Im happy with the "go" part, but it takes a long second to get there.
Im thinking accelerator pump in the carb? Ideas please... Car is a 76 L48 w/ Edelbrock Performer RPM manifold, Edelbrock Performer 1407 750 cfm carb. Previous owner was told it has "mild cam". True dual exhaust w/ Flowmaster super 44's. Replaced the typical "tuneup" parts and set to stock timing last year.
Thanks in advance for your help.

Is the car an automatic? How mild is the cam? Has the car always been this way? If the answer to the first and third questions are yes, Im going to speculate that you have too much cam for your torque converter.

Thanks for the reply. Car is a 4 speed. I don't know the cam manufacturer or any specification other than it is not stock. And yes it has always been this way since Ive owned it (6yrs). It also has the stock "rams horn" manifolds, but I've heard they aren't restrictive enough to be worth changing over to headers.

Well then the converter theory is out, but you still need to know what cam is in there. When does it seem like the car "comes alive"?

What gear is in the car, and please describe when the car does what you describe.

Is it that you are leaving off idle, punching it and the car lags, or is it that you are cruising at speed in a specific gear, punching it and then it lags?

The more info the better

On a weird side note....having an awful lot of interaction with LI folks on here today!:cool:

Overcarbed!
 

G'day,

There is your problem, the carb is too big for a low compression, low horsepower L48. If you MUST use a Holley, then go to a vacuum secondary 600 cfm and it will make a huge difference.

Best of all, fit an original Qjet that is in good condition or has been reco'd by someone like Cliff Ruggles, even if you have to use an adapter. Ideally, swap the manifold for one with a spreadbore pattern and you won't need an adapter.

No matter what you do to an L48, you won't make too much horsepower to overcome the flow capacities of a Qjet, or even a 600 Holley.

Good luck.

Regards from Down Under. :cheers:

aussiejohn

BB Dave: either off idle, or cruising and punching it gives the lag. Any RPM, any speed. Car has stock rear and trans. Didn't notice you were from LI, but the mild winter is getting me out early!
Aussiejohn: I had a feeling I would be hearing that from someone...It seems the carb/manifold is better suited for a different setup than I have, but I didn't think it would cause the lag I'm experiencing?
Thanks.

I had a serious lag when accelerating too. I have a Holley carb on a GM Performance 350 HO crate, but I the problem/solution may be similar.

I was able to SEE the evidence of the problem when my car was on a dyno a couple of years ago (before I got all the tuning figured out). I could see the car go extreme lean on the AF meter when I punched it.

I fixed the problem by 1) replacing the accelerator pump diaphram, 2) increasing the size of the squirters, and 3) replacing the original accelerator pump cam with a more aggressive and longer squirter cam.

Make sure your timing is adjusted correctly first. I had to replace the springs in my distributor with the lightest in the kit to get the advance to come in sooner.

To check condition of accel pump, just pop off the air cleaner, open the choke plate, exercise the throttle linkage to WOT, and see how much of a 'squirt' gets dumped into the primaries. If none...or it's weak...there's your problem. Otherwise, it's probably a timing issue.

On the other hand, my Holley 600 dp had a bog at ~2,200-2,500 RPM and is was from a rich condition from the squirters as the secondaries open. I replaced the 25s with 21s and the problem is gone. Note the A/F goes down to ~10:1 at the point of bog.

http://www.largescaleonline.com/eima.../Dyno_Pull.jpg

Is it worth a dyno test to troubleshoot this problem? What does it typically cost?
Seems easier than hit or miss (might be rich, might be lean...)

Usually 3 runs for $50 at a gathering. Be sure they do A/F ratio.

Thanks to all for your help.
Can any forum members from long island recommend a shop with a dyno?