I recently swapped cams on my 383. The car ran great with no carb problems before the swap. I went from a Bullit custom grind .525 lift 225/230 duration @.05 to comp cams XE294 .540/.562 lift 242/248 duration @.05. With the old cam I had 12-14inches of vacuum at idle and with the new cam 8inches. Timing is set at 15 initial and 36 total, distributer seems to be working fine. The carb has been put on a stock test engine and ran fine on there.
It always seems to run very rich at idle and doesn't want to idle at the correct rpm. I put in a 4.5 power valve and I have set the mixture screws several times. I have also bought a proform main body and tried larger air bleeds with no results. i have trouble with the idle in park being to high(1400rpm) if it idles at 800 in drive. I can adjust the position of the rear butterflies to correct this and get it to idle at 1000 in park and 800 in drive but then it is only idling on the front barrels. It runs great at full throttle if I floor it but at part throttle it sputters and acts lean..I think because of the position of the butterflies causing a a transition problem between the idle circuit and main circuit. Anyone have any suggestions? Thanks in advance for any help.

 

lol...welcome to the world of a big cam. 800 isn't very high for a 24x duration cam. What kind of vacuum are you getting out of it?

 

The idle is rich because the fuel is still burning when the exhaust valve opens. You need more itial timing to over come the EGR effect at idle of the big cam.

remove the distributor cap and rotor. remove the advance weights and springs. Tie wrap the distributor advanc mechanism to full advance. make sure the tie wraps are pointing down so the rotor will go back on.
Use small, thin tie wraps.
reinstall the rotor and cap. retard the distributor a bit and start it. set the timing with a light at 36deg BTC with no vacuum advance. reset the carb idle speed and mixture screw once the motor warms up.

Now the motor will burn the fuel at idle and the carb throttle blades will be at the right position at idle.

Now if the car is hard to start with the distributor locked out, have it recurved to allow more initial timing like 25deg+ at idle and the same 36deg at max advacne.
so 11 degrees of distributor advance travel
Give it as much initial timing as the starter will tolerate.
Don;t be shy.
You can reconect vacuum advacne to ported vacuum.

 

Thanks for the suggestions, I'll let you know how it turns out. I'll recurve the distributer tommorrow. I have a MSD HEI so it allows for a lot of adjustment. Jester, I have about 7-8 inches of vacuum at idle with the new cam.

 

Locking the distributer at 36 degrees helped a lot, the car is much easier to drive now. The starter strains a little to start the engine with that much advance but it seems to be ok. It idles much better and has more vacuum which helps the power brakes. I still have a slight part throttle stumble but I might be able to tune it out when I have more time to play with it. Thanks for the suggestions.

 

I had to respond because your combo is almost identical to my 69 Camaro minus the fact I had Edelbrock RPM heads. Even the ET is the same (12.03 @ 112). I love the cam and ran into the same problem. I had 6 inches of vacuum at 1100 RPM in gear. I agree with adding intial timing setting. You may even need less total because of the quality of your chambers. Here's what worked on my car.

Drilled holes in all 4 thottle blades.
Blue pump cam in front.
37 front squirter
Brown ? rear squirter in rear.
35 rear squirter
35 total timing 18 initial (MSD Billet)
3.5 power valve
75 front 83 rear jetting
Victor JR. intake

When you have the carb off the car look at the idle tranfer slots in the throttle plate by the blades. Set the front and rear idle by making the slots a perfect square. This is a good baseline for equal idle. If you don't have holes in the thottle blades yet put the carb on. If the idle is close after you set the mixture screws you're good . If it's low drill the holes.

 

How tight is the converter?

 

3200 on the foot brake

 

Dang 'b busse' did you bug my house. That list looks very familiar right down to the RPM head, but an XE284 - 7psi@6300ASL.

However I bought two sets of Holley throttle plates from Summit of differing hole sizes.
I used to run the brown on the 50cc pump, till it locked my throttle wide open. Thank G0D I had a kill switch in the middle of the dash. There's no thinking involved, just hit the kill switch

BTW: I used to have a horrible stumble, till I replaced my big 830 body for a proform 750 body. I had so many factors that my stumble could of easily been predicted on paper. High Altitude, single plane, 830CFM carb, big cam. Stupid me

Ron

 

Dont drill holes in the throttle plates. Here is a better way. If you need more idle speed (airflow) then just create a small adjsutable air leak into the maifold at the carb base. Simular to a Idle air control motor on a TPI car.
Use a pepcock to adjust the airflow.
The motor is not fussy as to where the extra airflow comes from.

But first make sure you have a functional PCV system hooked up. This extra little air leak at idle is part of the carbs design. Without it the throttle blades will be too far open at idle.

As a note: I've run much larger race cams with less manifold vacuum and did not have to resort to drilling holes or even using the Auxillary air bleed to get the idle right.
the increased initial timing and referencing the throttle blade position is all I needed to do. Don't forget the PCV valve.