427F-Bird

iTrader: (1)

Im in the process of putting together a 86 Firebird. The engine is a 427 Big Block. It is a tall deck. Other than a camshaft, it is stock. The carb i have on it now is a edelbrock 1405. 600 cfm. I was wondering what i could do to lean out the mixture, as the car is running really rich right now, to the point that it will not idle at all. Also, could i possibly be running to much cam. The camshaft specifications are as follows. It is summit part number SUM-1303

Cam Style:Hydraulic flat tappet
Basic Operating RPM Range:3,000-6,500
Intake Duration at 050 inch Lift:238
Exhaust Duration at 050 inch Lift:248
Duration at 050 inch Lift:238 int./248 exh.
Advertised Intake Duration:296
Advertised Exhaust Duration:306
Advertised Duration:296 int./306 exh.
Intake Valve Lift with Factory Rocker Arm Ratio:0.540 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio:0.540 in.
Valve Lift with Factory Rocker Arm Ratio:0.540 int./0.540 exh. lift
Lobe Separation (degrees):114
Intake Valve Lash:0.000 in.
Exhaust Valve Lash:0.000 in.

Thanks in advance for any help.

MrBrooks

You may want to look at stepping up the size of your carb. That many inches will have a very hard time with no more flow than 600cfm. The basic formula for cfm is, cubic inches times max rpm divided by 3456. For you that would make 803cfm. A good 750 would work though. Edelbrock carbs will ALWAYS idle a little on the fat side--- nothing you can do about that other than get rid of it. If you couldnt tell i'm a Holley guy. But anyway it's usually best to go a tad bit undersized on carb. The specs on that cam are screaming for a 750cfm Holley model 4150. Thats the legendary Double Pumper. But thats jus my opinion.

scottsz28

+2 get a bigger carb, i have a 600 on my 350 and its working pretty good, i couldnt see someone stickin it on a 427, if you had that rebuilt dont skimp out on the carb, get a good 750 at least if you wanna stay with edeldbrock run and grab the 350 follow all the steps on their website or in the box then come back if your still havin problems.

rat infested

Would agree on a bigger carb
I had a 650 vac sec on my old 402BBC and suffered similar probs
went to a 750 vac sec and prob sorted !!!

427F-Bird

iTrader: (1)

I probably should have checked the responses to my my question before now. I appreciate the responses, but im missing something here. How would putting on a bigger carb solve the problem of it running rich?

xpndbl3

iTrader: (5)

have you adjusted the idle mixture screws as per the instructions on edelbrocks site? that would cause the running rich problem at idle. More timing at idle and less total mechanical advance would keep total timing in check and clean up the idle mixture as well.

battyice

With 427 cubes and that large of cam, the engine needs a lot of air to idle properly. When you open the throttle blades to give the motor the air it wants, you have to open them too far. Basically, the idle transition slot starts to get uncovered and you lose control of the idle mixture. The easiest solution is to get a 750 cfm carb. I have a camshaft similar to yours in my 355 and had the same problems with a 600 holley.

If you REALLY wanted to keep the 600, you can drill holes in the throttle blades in order to give the engine extra air without opening the throttle blades too far. This is a popular mod to Q-jets. I'm sure you can find some information online if you want to go that route.