C3: Vacuum leak?

[Dan Pepper]

1969 350/350 Coupe: I have been experiencing engine hesitation while at highway cruising speed / 3,000-3,500 RPM, and suspect a vacuum leak. I have checked timing, carb settings, ignition componants, checked all ports, gaskets, etc. and everything looks fine.

If this is a vac leak, could it be coming from the headlight/wiper door vacuum system? Both the lights and the wiper door work fine - but I'm wondering how much vacuum it takes to keep the system under pressure, and if the system may have a leak that is causing the hesitation at speed. I have checked the vacuum port with a guage and the needle stays pretty steady at around 12-14".

I'm going to block the vac port and go for a cruise to see if that makes a difference. And if it does, what is the best way to chase down a vacuum leak in the system?

[William C.]

Re: C3: Vacuum leak?

Aneasy way to check the vacuum system integrety is to run the car for a short period, then turn it off. The system should hold vacuum well enough to operate the headlamps after the engine has been off for at least 20 minutes. I doubt that a vacuum leak is the source of your problem at 3000 rpm.

[Jim T.]

Re: C3: Vacuum leak?

When you checked your timing, did you test your distirbutor vacuum advance cannister was holding applied vacuum?
Another area to check is to remove the distributor cap and rotor and remove the centrifical advance springs, remove the advance weights, and clean the pivot posts and weights. I don't know if this is a recommended procedure, but I use a dab of point rubbing block lubricant on the posts and where the advance weights slide.