engine not producing enough vacuum

-
J

jroadstar

Hemi child
Joined
Jan 7, 2015
Messages
4
Reaction score
0
Location
Bellville
Hi everyone
I'm in need of some help.
I bought a car with a 440 6pk setup in it and I've found that the engine isn't making enough vacuum to operate the brake booster or the outboard carbs so I need some suggestions as to what maybe wrong so I can correct it.
I can offer this info to try and help.
Lunati cam number 10230703
Advertised duration is 271 int 279 exhaust
Advertised lift is 494 int 513 exhaust
Lobe separation is 110
Has 1.5 ratio rockers
Engine is producing 10 inches of vacuum now but lunati says it should be at 15 to 16 .
SO WHERE DO I GO TO LOOK AND CHECK NOW?
PLEASE HELP

THANK YA'LL IN ADVANCE
 
initial timing?

The outboard carbs won't open smacking the throttle in your driveway.
 
Initiall timing is at 10 degrees
And no they won't open up and the diaphragms on the carbs are new
 
Not near enough initial timing. I run stock 318's with that initiial timing setting.

Crank as much initial timing in that the starter can handle when hot and readjust the carbs. That cam should be good with about 16-20. If it takes more, OK. You'll need to alter the mechanical advance to keep your total number in spec.
 
crackedback said:
Not near enough initial timing. I run stock 318's with that initiial timing setting.

Crank as much initial timing in that the starter can handle when hot and readjust the carbs. That cam should be good with about 16-20. If it takes more, OK. You'll need to alter the mechanical advance to keep your total number in spec.
Click to expand...

:burnout:
 
Vacuum secondary carbs do not operate on engine vacuum. So the low vacuum reading your getting has nothing to do with the outboard card not working.

Hook you vacuum advance on the dist to manifold vacuum, that will help out a lot. Make sure you don't have really LIGHT advance springs either. You may have to use a limiter plate/advance spring kit to re-curve your dist.

Also you need to make sure the center carb is adjusted correctly. Its a pain but if its wrong it will run like crap.
 
Thanks for the input so far.
That car has MSD ignition with billet mechanical advance dist. Also found a guy with a 69 numbers matching 440 6pk to compare with all the vacuums appear to be hooked up right so I'm still lost lol but I'll check the advise about cranking as much advance as I can to see what that does in the morning.
 
That is pretty low, I built a 461 stroker pontiac wtih the voodoo 268 and it pulls 17" of vacuum. The pontiac does have few more cubes and a longer stroke, but I would think 14 to 15 would be about right for a 440.
 
I got it after a week of trying it turned out to be the ported vacuum fitting on the back of the intake found it by accident twisting on the hose.
 
Good find. On the carbs - they are typically slow opening, and smooth enough that you may not feel them coming on. Take a small piece of wire (like a few strands of copper from a 16gage wire) and wrap them around the shaft tight enough that they can't fall off but lose enough to slide easilly, and keep them up against where the rod goes up into the vacuum pod base. Leave enough length for the wire to contact the sides of the vacuum pod passage the rod passes through. Then drive the car.... The carbs - if they open - will force the wire down the rod a little. Then when you look you'll see the wire has moved. Or replace the springs in the vacuum pods with the light purple springs from Holley. Also make sure the base plate gaskets are not keeping the outbaords from opening very much. If they are not placed properly they can hang up the throttle plates.
 
If you are still at 10 initial, it has a bunch better idle quality available by fixing that setting..
 
You must log in or register to reply here.
-

Back
Top