Problem with Holley 4 bbl
It CAN idle at 700...it just doesn't like it. 850 is far more stable.
PVC is connected to the throttle plate port on the back of the carb and gets full manifold vacuum.
Here are the cam specs as provided by Oregon Cam Grinding.
Cam lobe lift .359 intake .372 exhaust
Duration @ .050 - 235/247
Lobe separation 110
Intake center line - 106
Dart_68,
A lot of things are not adding up.....
Only 5" of idle vacuum, & you want it to idle at 700 rpm? I doubt that will happen.
If the low vacuum is from a long duration cam, hard to believe that both pri & sec t/blades are almost closed, because the engine should need a lot of bypass air for it to idle. The engine gets this air from opening the t/blades further, drilling t/blades, etc.
Do you know the cam specs & comp ratio?
The secondaries are almost closed. I cracked them open about 1/3 of a turn on the screw.
WIKI says Lakewood Colorado is at 5518 ft elevation. That in itself is a problem.
For a short time, I ran the 292/292/108 Mopar cam in my 367(11.3Scr at that time.). The beast measured
[email protected] on my equipment. It idled at 10/11" at 750 at my 930ft elevation. It would idle down to 600 at about 8* advance. I normally ran it at 14*. Mine needed the Transfers to be a lil taller than wide, not much. Holley 750DP. I ran it with the secondaries closed up tight but not sticking. She asked for one small bypass hole in each primary blade of about 3/32. 4/32 was too much, and I had to solder them shut and start over.
you said; "PCV is connected to the throttle plate port on the back of the carb and gets full manifold vacuum."
Is this correct? I thought all Holleys had the PCV port on the front? The back port is for powerbrakes. If you run the PCV to the back, then the back cylinders will run lean. When you run the PCV to the front the air mixes with the transfer fuel and everybody gets a fair deal.
You said;
Duration @ .050 - 235/247
Lobe separation 110
Intake center line - 106
This looks sortof like a Whiplash/Thumpr, with a huge 12* split, but the LSA of 110 is too wide to be .
My current cam is 230/237/
[email protected] and looks to be about one size smaller. It idles at over 11", and will pull the Barracuda along on flat level hard ground at 550 rpm @5* of timing. It will go to 500. I still have that same 750DP on it, but the holes are ALL soldered up now.
If I had to guess I would say that your intake is sucking oily air from the valley. You can prove this easy enough; just flip the PCV out and plug the hole, and plug the breather. Then put a vacuum gauge on the dipstick. Start it up, and the engine should IMMEDIATELY begin to build pressure Shut the car off before it goes past 3 psi, else you risk blowing the rear cam plug out. If you have vacuum there, that is NOT right.The intake has to come off.
But if there is NO unmetered air entering the engine, and the timing is between 14 and 18 degrees; then I would suspect .................
Oh wait, I have never tuned an engine at 5518 ft elevation, so IDK, I can't help you man. Maybe 5inches at 5518ft elevation is correct, IDK
IMO, with the transfers square and the secondaries barely cracked, the engine should not be running in the first place. If it was sucking air somewhere that air has NO fuel in it, so it would just be worse; and the mixture screws would be working over time to keep up.
My next guess is that the PCV running in the back is drying those back cylinders up, and she's running on the front four, dragging the others along.
With an IR gun check the idle temps of the back cylinders versus the fronts.
If it was me, I'd go look at that carb again; it should have a PCV port on the front.
