Carbs

Clois Harlan · #1 (**permalink**) 07-01-2002, 08:12 AM

Last week I replaced my Holley 750 with an Edelbrock 750 but I seem to have lost a little when I did. Now when I accelorate hard my car seems to bog down and then grab after a little flutter. I didn't have this problem before so I am at a loss as to what to do. However, once it does catch it jumps to life.

Tonight I will re-check my timing and air fuel mixture as well as my springs in my distributor. All my plugs and wires are new as is my Holley fuel pump. Plug gap is about .045 and fuel pressure is at 6#. I am not sure of the size of my jets or pins.

Any suggestions?

Thanks,

Clois Harlan

Pete C · #2 (**permalink**) 07-01-2002, 08:24 AM

Clois,
I'm having the same problem with my dual Holleys. I'll start by checking for vacuum leaks, gas levels, accelerator pump and adjustment screws. Let me know what you find.

Pete

wilf leek · #3 (**permalink**) 07-01-2002, 08:33 AM

Clois - if the bog is immediately as you put your foot down, then probably the accelerator pump needs a bigger (or smaller?) shot - there are different holes in the linkage arm on the edelbrock carb you can choose from.

If it's after that, and at WOT, then maybe the secondary jets need to be looked at. The step up valve springs could also be the cause, but they should not affect WOT.
A bit more detail, such as at what revs this does/ does not happen etc could help the diagnosis. Is this a quick transient effect, or does it persist for a few seconds?
IMHO a session on the dyno is the best way to sort carb problems out. You can't fool an air-fuel ratio meter!

I do find that on my own car, with Edelbrock 800cfm carb, it does not particularly like WOT below 3000rpm in the higher gears - revs pick up too quick in the lower gears to make any difference!

Clois Harlan · #4 (**permalink**) 07-01-2002, 08:41 AM

Yesterday as I was entering one of our freeways I was rolling at about 40 mph in second gear, I decided to put my foot to the floor while in second gear. The first thing that happened was the carb coughed and sputtered and then grabbed and basically launched and then as I hit third gear the same thing but not as bad. I am shifting at about 4500 rpm.

Roscoe · #5 (**permalink**) 07-01-2002, 08:47 AM

Clois,
Link to Demon Carb Tips and Troubleshooting. I imagine the remedies are the same no matter whose carb you have.

http://www.priveye.com/dls/Demon2.jpg

Roscoe

Mr.Fixit · #6 (**permalink**) 07-01-2002, 10:13 AM

If it coughs then picks up, you have a flat spot in fuel delivery. The carb is not squirting enough gas with the accelerator pump to cover up that hole, a cough is going lean. If it chokes up then cleans out (like my chain smoking uncle with emphesema) then it is rich, or your secondaries are opening too early causing a lack of velocity past the boosters, and thus poor fuel metering until airflow picks up and you need the secondary butterflies open.

JAM1775 · #7 (**permalink**) 07-01-2002, 11:49 AM

Sounds like the accel pump. You may need a bigger squirt or perhaps just check your pump levers and make sure they are adjusted to specs. My Demon actually required a slight gap while my new Holley requires a zero gap. If you hold the bottom nut and go counter clockwise on the top one you will tighten the pump which should deliver the squirt on call. ..instead of waiting for your motor to pull down the fuel .
Edelbrock is 800-416-8628.

Clois Harlan · #8 (**permalink**) 07-01-2002, 12:23 PM

Thanks everyone, I will play detective tonight and see if I can't get it all dialed in.

Clois Harlan

Clois Harlan · #9 (**permalink**) 07-02-2002, 09:07 AM

Made a few changes ie: accelerator pump adj rod, changed springs in my distr (MSD 6A went w/ blue and small silver), all my advance should come in by 3100 RPM, also retarded my timing about 2 degrees.

I don't know if I have everything dialed in or not because it has rained yesterday and is sprinkling today. I will bring this back up when I get to test these changes. Setting in the garage it seems just fine but I won't know for sure until I can get on the road.

Thanks,

Pete C · #10 (**permalink**) 07-02-2002, 09:25 AM

The problem with my Holleys is gas leaking past the metering plate (through power valve plug) and bogging the engine!

Cheers, Pete

Whaler · #11 (**permalink**) 07-02-2002, 11:15 AM

Clois just for my own info, I was wondering what stop busing you are using now and also what springs were you using before this change.

"Made a few changes ie: accelerator pump adj rod, changed springs in my distr (MSD 6A went w/ blue and small silver), all my advance should come in by 3100 RPM, also retarded my timing about 2 degrees. "

What is your initial or static set at with the 2 degrees taken off?
What RPM is your idle now?

Tim

Whaler · #12 (**permalink**) 07-03-2002, 12:07 PM

Quote:

Originally posted by Whaler
Clois just for my own info, I was wondering what stop bushing you are using now and also what springs were you using before this change.

"Made a few changes ie: accelerator pump adj rod, changed springs in my distr (MSD 6A went w/ blue and small silver), all my advance should come in by 3100 RPM, also retarded my timing about 2 degrees. "

What is your initial or static set at with the 2 degrees taken off?
What RPM is your idle now?

Tim

Jim Downard · #13 (**permalink**) 07-03-2002, 01:12 PM

Clois,
I had the same problem with two different carbs. Buy a jet kit for the carb, ( I think the kit will be for model 1411 carbs) and use the instruction manual that came with your carb. The chart in the back with tell you what jets come std. in the carb. I ended up going two steps rich in cruise mode and one step in power mode. That pretty much took my flat spot away. You'll like the Edelbrock for the ease of changing the jetting.

Good luck,

Jim Downard

Clois Harlan · #14 (**permalink**) 07-05-2002, 06:28 AM

Whaler,

Sorry it has taken so long to respond but we have been at the lake. Plus it had rained the first part of the week keeping my snake off the streets. But finally I got it out and seem to have solved most of my problems.

To answer your questions I moved my acel pump rod down one notch and increased my fuel press to 7#. Also, I went from the heavy silver springs to one blue and one small silver spring on the advance. I did not change my stops yet. I have a session with the dyno next Friday ($100/hr plus $20 for the air fuel calibaration devise). I hope we can pull every avail horse out of this bad boy for the Run and Gun in September. Hopefully, you can make it to Run and Gun and we can exchange notes.

Jim- I have a jet kit and will be taking it to the dyno session and will let everyone my results later. Probably after the 12th of July.

Clois

Scott S · #15 (**permalink**) 07-06-2002, 08:20 AM

If you are having trouble with a E carb bogging on acceleration it may have the wrong metering springs, get a spring kit and put in a slightly stiffer spring.

bran3b · #16 (**permalink**) 07-14-2002, 05:57 PM

Clois,

Did you fix your problem? I think that I am having the same problem, which was diagnosed as a lean condition at full throttle caused bu no fuel from the secondaries. The primaries work great, but when the secondaries open at 3500 - 4000 RPM they do not add any fuel. After 4000 RPM the fuel starts to come in, but still not enough to make the mixture right.
I am going to try a stiffer step up spring, and bigger secondary jet.

Mr. Fixit,

You mentioned the secondaries opening too soon, is there a way to ajust that on the Edelbrock Performer carb?

Bran

Mr.Fixit · #17 (**permalink**) 07-19-2002, 11:12 AM

I don't know a damned thing about edelbrock carbs. I am a Holley man through and through. They seem to be the choice in many racing classes, are OEM for most musclecars, and are soo simple. Customers with really bad carb problems, I would start by putting on a prepped holley to see how well it runs with a good carb, and the customers would often just buy that carb because the performance was better than expected.

xlr8or · #18 (**permalink**) 07-19-2002, 02:21 PM

Clois and Bran3b,
The metering spring change on Edelbrock carbs are really only useful for flat spots in transition from cruise mode to power mode. If your problem occurs during transition from mid throttle to heavy pedal the springs probably won't do enough. When your already up at 3000 rpm + and good bit of throttle it is most likely going to need a pump adjustment and jet/rod change since your are already beyond the cruise/power mode switch.

Remember keep going rich until it doesn't get any better when jetting and then back off one step. Better a little rich than lean.

Campy · #19 (**permalink**) 07-25-2002, 08:46 PM

Clois,

Your approach to your problem is correct however, there is one thing I would have done differently. Trial-by-error diagnostics should involve making only ONE change followed by testing. This will give you an indication if you are on the right course. When you make two or more tweaks it's sometimes hard to determine which one made the difference. I would have only modified the accel pump linkage and tested that. I am pretty sure your timing advance has nothing to do with the flat spot.
When you think about it, the advance takes place while the engine is spooling up, not before.
Good Luck

Clois Harlan · #20 (**permalink**) 07-25-2002, 09:04 PM

Campy,

I seem to have found the correct tweks for now. Everything seems to be performing very well. I agree with your method of changing only one thing then test but I was working in a narrow window. Luckily I think I have everything where it should be.

Thanks everyone. Lots of good ideas come from this site as with many others here I have a lot of respect for the information I have received. Sometimes you know the answer but you just want someone else to say for you.