Expert: Kevin Pilotte - 9/13/2009

Question
QUESTION: Kevin,

Thanks for your help on the previous question. I have another.
with timing at 10-14 initial
304 amc 1979
the jeep stumbles intake pressure 15
with timing at 24 jeep doesn't stumble intake pressure 17 runs like a champ
should I be worried about the timing?

ANSWER: As long as you don't have ignition ping. When you say intake pressure, do you mean manifold vacuum? If so, it should be 18-21 inHg at idle. Sure you don't have a vacuum leak somewhere?
You might just be masking a real engine problem by having to use so much advanced timing.

---------- FOLLOW-UP ----------

QUESTION: Yes manifold vacuum is what I meant.
I took a can of carb cleaner around the intake and the hoses with no spike in rpm.
I do have a mild torque cam in it will that make manifold vacuum go down?
I have PCV and Power brakes connected to the carb/manifold. Can something there cause the drop
The needle is steady on the gauge so whatever it is leak or no leak it is steady.

Could it be a piston or a valve or something?

Answer
Ahhhh,
Another piece is added to the puzzle. A non-stock cam can give you those manifold vacuum readings at idle.
If your engine is not pinging with the current ignition timing and it runs OK, leave it.
As for the brake booster, try removing the hose from the booster and plugging it to see if the engine RPM changes. If it does change while your finger is over the hose, you have a booster leaking.