390 RPM Performer Engine off idle miss/surge

[leavittt]

I'm having this problem & hopefully some of you can help me out. I have a 1970 Ford F100 with a 1968 FE 390. It has about 200 miles or less on it since I rebuilt it. It's bored .030 over with the Edelbrock Performer RPM package-RPM cam, RPM Intake, Edelbrock 750 manual choke carb(1407), Edelbrock RPM Heads with the 428 Cobra Jet sized valves, Headman headers and brand new MSD wires and Ignition Box (MSD 6AL w/built in rev limiter). All of these parts are brand new. Also the cap, rotor and plugs are all brand new. Ever since I got it back together it runs great except for just off-idle. When you're lugging it at about 1500-1800 RPM there's a miss/surge. I have a AEM Wideband A/F mixture gauge and when it's missing the gauge jumps up lean anywhere from 15-20. If you punch the gas, it clears right up, goes down in the 13's and runs like a scalded rabbit. I checked my vacuum at idle and it reads a little low at about 6". When you rev it up a little, the vacuum goes up to 10" and above. I've replaced the plugs since the rebuild and nothing changed. I've changed my carb flange gasket as well as my air horn gasket. I've also blocked off my power brakes to make sure there wasn't some kind of vacuum leak there. I've tried all different needle and jet combos and that doesn't seem to affect the miss at all. Right now I have a #13 jetting combo(from the Edelbrock carb owner's manual) which is a .116 main jet and a .071 x .047 metering rod. Also the idle mixture screws don't seem to have any affect on the miss either. This is a little odd to me, but the truck runs best with the timing at 25 degrees advanced. That seems a little too far advanced but I'm not sure. The elevation here is about 4500 feet. I've looked for a vacuum leak but can't find one anywhere. Hopefully someone can give me a little help. Thanks.

[FORD428CJ]

Double check to make sure your intake bolts are tight. Also pull the plugs and check them to make sure you don't have a vacuum leak (read the plugs). Timing seems a little to high. Depending on the cam, it could be 10 to 16. All in by 2,500rpm (give or take a few RPM's) 36 total!

Also you may have to adjust your accelerator pump. May need to come on a little sooner from the sounds of it. JMHO

[binder56jd]

good advice--not all castings are perfect u may have got a blem--hope not --lot of needless work--good luck--reads like a good set up--u may need to tinker with the timing curve

[floyd67]

i have a simalar set up my brand new carb is now in the big bin i put on a holley now it runs great i have never had any luck with edelbrok

[leavittt]

Thanks for all the advice. I'm going to give these ideas a try and see if I can get the off-idle cleared up.

[binder56jd]

yep--i am holley on my v8's

[peanutman]

I had a simular problem recently. Rebuilt carb, new wires and such, new vac advance, retorked intake, rebuilt carb again. My problem would come and go. Vac test showed a vac leak when it was acting up. Found out i had a bad dizzy, the plates under the points or a short under the plates must have been the problem- throwing off my timing. Replaced dizzy with a brand new rebuilt and it fixed it

[FORD428CJ]

Using a Hand Vacuum pump, you can test it and see if it is holding or not. JMHO

[DuckRyder]

It is also my understanding that Edelbrock has sold at least two diffrent RPM cams and one of them is very radical lobe separation and soft down low. Mahem Bob (may he rest in peace) had to run a 4500 (IIRC) rpm converter to get it to launch.

When they say "not intended for heavy vehicles" they mean it.

What I'm trying to say here is that it may just "do that".