Slightly erratic vacuum
Thread Starter
Instructor
Joined: Mar 2013
Posts: 100
Likes: 0
Slightly erratic vacuum
You folks have been a tremendous help. I was having a loud clicking under the valve covers this week and because of these forums I was able to find a loose rocker and put a half turn on it, making the noise disappear completely, and If im not mistaken the car runs a little smoother now.
I was checking my vacuum at the PCV port on my carb and it jittered between 16.5/18 or so psi. If i hooked it to the pert just to the right of it these are my readings.
The car can't be timed with a light because its not a stock engine/harmonic balancer. I will attempt to time it using vacuum first I was just a little interested in this reading. My plugs have gotten fouled lately and my mechanic said the carb was out of tune. So I have 99 small problems but the knock aint one. lol.
What do you folks make of that reading?
I was checking my vacuum at the PCV port on my carb and it jittered between 16.5/18 or so psi. If i hooked it to the pert just to the right of it these are my readings.
The car can't be timed with a light because its not a stock engine/harmonic balancer. I will attempt to time it using vacuum first I was just a little interested in this reading. My plugs have gotten fouled lately and my mechanic said the carb was out of tune. So I have 99 small problems but the knock aint one. lol.
What do you folks make of that reading?
Melting Slicks
Joined: Jul 2010
Posts: 2,503
Likes: 33
From: McGrady NC
St. Jude Donor '15-'16
Valve adjustment problems can cause slightly erratic vacuum readings. So can worn cam lobes which will give different vacuum signals for each cylinder and shows up as a jumpy needle. Check the plugs for significant differences in plug color and condition. Undampened vacuum gauges can also give bouncy readings. If the valves are properly adjusted and the car runs good with minimal or no oil use, then I would give it a tune-up soon (including a valve adjustment since you already had a loose one) and not worry about it.
Search the forum on how to put a timing tape on your aftermarket balancer. It will be very helpful in tuning your car properly.
Search the forum on how to put a timing tape on your aftermarket balancer. It will be very helpful in tuning your car properly.
Last edited by CaseyJones; Apr 19, 2013 at 08:35 AM.
Racer
Joined: Apr 1999
Posts: 422
Likes: 3
From: Oxford MI
Given that you have already found on rocker arm out of adjustment, I would suggest you go methodically through all of them to make certain they are set correctly. If you still have some gauge flutter the next step would be to adjust the card idle screws. Maybe the first thing to do though would be to get a balancer with a timing mark.
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Vac leak or bad valve.
Vacuum is measured in inches of Mercury ("Hg). Can't read anything in your profile but most of the smog motored C3s with stock engine willhave 18"-20" vacuum. A fluctuating vacuum indication usually is a bad valve (leaking) or a vacuum leak itself somewhere.
cardo0
cardo0
