can't get this to go away. need an expert mech.

[66hemi]

Guys, please help me get this issue to go away. I have a 440 4spd with 4.10 rear. 509 cam, .30 over, torker 2 intake holley 800 dblp. timing is at 18, vac is about 8. Idle seems fine. while cruising the car is jerky. but when you give it a little gas it is fine until it gets to the Plato and then is jerky again. I think I have changed just about everything but the key switch! under slight load seems fine. What would cause this! the holley jets are 72 front 78 rear.
I tried a edelbrock 750 and same thing but the jets might be wrong in that carb for my car. I have both jetting kits for the holley and the afb if someone can give me an idea of the jets that would be close.

[RD]

what is your fuel pressure at.. when was the last time you changed your fuel filter?

[66hemi]

I'll have to check but it seems funny when you nail it, it goes strong. it doesn't seem to be starving for fuel but I will certainly check the filters and psi. I have a carter fuel pump on it and it said on the box 8psi.

[RD]

8psi is too much for a edelbrock.. you could be flooding it out.. it may be a tad on the high side for a holley (depending on the holley) also.  pull your plugs and see what they look like.

[66hemi]

I'll do that. The plugs all look like they are burning ok. little on the dark side from all the idling. I have put 3 sets of plugs in new wires cap rotor push rods had the heads redone tried different electronic boxes distributors balast and wiring harness fron the orange box to the coil and distributor. nothing has changed it. Do you think it is carb related? I have taken parts off my other car that is running fine just to see it might be the problem.

[RD]

i had a eddy on my 400 one time and acted the way you are saying.  it was due to the carb being insufficient to handle the duration of the cam I had in it.  it could very well be an issue of not enough vacuum.  do you have power or manual brakes?

i think it is carb related to be honest.  going from a holley to a eddy will just exacerbate the situation if you ask me.  Ron, is more of a carb guru than i am, he will chime in when he gets the chance.  i am sure he will have the answer you need.

[66hemi]

I have power brakes. What should the vac be on a 440 with a 509 .30 over?

[Rolling_Thunder]

hmmmm    440ci with a .509 cam (I assume the MP) -  vacuum will not be much...   that cam has a lot of O-lap and does not make much...     

[charger Downunder]

vacuum advance could that be the cause

[66hemi]

I tried a different distributor and the same thing. Could the voltage regulator do it? I'm still thinking it is jetting? any I dea's of what the jetting would be close.

[charger Downunder]

try 76 front jets while there check and see what power valve you have in the holley

[66hemi]

OK update, I checked the fuel psi and it is 5. I put the edelbrock afb 750 back on to see if it made a difference. It was worse. I also put a new voltage regulator just to see if it would make a difference. It didn't.  It seems to be around 1400 to 2500 rpms. What else electrical could it be? There is no backfiring sneezing thru the carb, all plugs look like they are burning. No hesitation when stomping on it going thru the gears. Just a very jerky ride when cruising with your foot in one place. This sucks. Its my favorite one to drive too.

[flyinlow]

1 Try different gas. Gas companys are switching blends as the weather warms.

2  If you have vacuum advance try disconecting it.

[hemi354az]

In the old days, that is how a car with a broken motor or transmission mount acted.

[maxwellwedge]

Sounds like pretty low vacuum.

What is your total mechanical advance and at what RPM?

[elacruze]

Mine's a 440 4speed with .509 cam, 11:1 compression, and M1 single plane intake. I hate it. Below 3000rpm it's impossible to tune-either it does what you describe, or it's so rich it fouls plugs. I traded a dual-plane Edelbrock CH4B manifold for the M1, and never should have. It drove perfectly with the CH4B intake.

[firefighter3931]

If the vacuum advance is still being used disconnect it and block off the port to the carb with a plug. Bump the base timing up to 20-22* and take a look at the total to see where it's at. It should be at 38* or less...if not the distributor might need some work.

From what you're describing it sounds like a lean surge which can be both timing and carb related. Vacuum advance is designed for a stock engine that makes way more manifold vacuum than yours does. If you're using vac advance, disable it and adjust timing as recommended. 


Ron

[66hemi]

Ok Ron, I'll try it. How do I set total timing? I don't have a tach. I do have the vac advance on but will plug it up.

[firefighter3931]

Ok Ron, I'll try it. How do I set total timing? I don't have a tach. I do have the vac advance on but will plug it up.

Total timing is a combination of initial timing and the mechanical advance that is built into your distributor. The newer MP electronic distributors have adjustable "stops" that can be used to limit the mechanical advance. For example ; if you dialed in 20* at idle you would need 18* of mechanical advance to achieve 38* total timing. The rate of advance is determined by the springs on the advance weights. Lighter springs bring the mechanical advance sooner....stiffer springs bring it in later.

First thing to try is disableing the vacuum advance and see how it runs. Advancing the timing at idle will increase manifold vacuum and make it run cleaner. Try it at 18* for now and see how it idles and runs.

**If you decide to advance the timing the rpms will increase (at idle) as manifold vacuum increases so you'll need to reset your idle speed.**


Ron

[66hemi]

Ok Ron,

I did a few things. I checked the fuel pump and it is 5 psi and has good flow. I put the 78 jets in the front but now realize charger Downunder said 76's
and changed the power valve to a new 65 it was a 75 in it that I was trying. I also cap the vac advance port on the carb. Set the timing to 18 and the result is it is running much better. Seems a little fat. Mostlikely my error with the 78 in the front.  I jumped on it and it seems a little sluggish and when I let off it almost quit, didn't want to run and smokeing a bit. I got it to idle and set it to around 850 or so (no tach). It seems to not really want to idle steady. After a rev it runs a little high then slowly drops. The vac is shaking from 9 to 10 where I have the idle set.  Thanks for your help so far everyone. I think we are almost there.