Hi all,


Car has finally turned up!!!


Following >3 months between warehousing and containerage - it was a surprisingly easy start with a some fresh fuel in the tank and a bit down the carb... so now parked in the garage and am assessing what i've actually bought!


first ask; the engine pulls 12-13 HG at idle - is this enough to run the factory lights and wiper door smoothly? - neither are fitted at the moment - I was slightly concerned this was because the engine had no vacuum - but now not sure as 12-13 HG isnt terrible?


many thanks for thoughts!


David

 

have you tried tuning the engine to increase the readings?
have you checked for vacuum leaks?
what year, engine, modifications, etc.

 

It's a 454 - with a hydraulic cam of unknown specs, worked rectangular port ls6 open port heads, headers (see other post! Lol), rectangular port intake and a Holley 750 double pumper..

I don't know whether it can be tuned out, or has vacuum leak (I've had it in my garage about 4 hours!) - but suspect that the combination of big heads, intake runners etc and a cam which certainly isn't a std grind are the culprits rather than an issue with the engine..

 

what is the idle speed when you are taking the readings?
do you have points?
if you have points have you set the dwell?
have you checked the timing at idle with the vacuum advance disconnected?
have you attempted to adjust the idle mixture screws?

 

First off, welcome to the club. Yes, you have enough vacuum to work the lights and wiper door properly. This is of course assuming your car's vacuum components are leak free, or could be made to be.

 

Possibly try to see if you can get the vacuum reading higher...but that will all depend if the engine will allow you to do it. A vacuum ague...as you more than likely know will be your 'best friend' here when setting the idle mixture and timing,

And I am also sure you know when you are attempting to tune your engine....make sure you take the vacuum supply for the headlights and wiper door/HVAC out of the equation. And I have also removed the hose to the brake booster and capped it off. Because on rare occasions...it is leaking.

For what it is worth....I just had to repair a vacuum storage tank for a 1969 ...because it had splits in the steel and would NOT hold any more than 11 inches of vacuum.

DUB

 

Factory produced Chevy engine will pull from 15-21" Hg, depending on how aggressive the cam is. Base level engine will pull 19-21" when new. Used base engines which do not have serious problems with valves/cam should produce 17" Hg or more.

To assess how much vacuum your engine is capable of producing, you need to disconnect [and cap off any open lines/fittings] ALL vacuum supply lines from the carb and intake manifold; then test for vacuum level at idle. If that measured value is significantly higher than what you have now, you need to diagnose and repair any leaking vacuum lines or leaking components. In general, the components and lines in the vacuum system should not lose more than 1-2" Hg vacuum when all are installed. The components most likely to be leaking are: the vacuum check valve, the headlamp and wiper door relays (the actuator cans may leak also, but the relays are the MOST likely of those two); the wiper safety switch (under the right-side wiper); vacuum brake booster (if you have power brakes).

To find those problem areas, do the "baseline" vacuum test first. Then add vacuum line back...one at a time...checking to see if the vacuum level stays nearly the same (no additional leaks in that added line), or if it drops significantly. If it drops, block off lines/components in that string until you identify the leak areas; then resolve them.

The process is pretty simple. You just need some caps to plug off open fittings, a couple of hand operated squeeze clamps (so you can block off vacuum without removing a vacuum line), and a vacuum gauge...which you already have.

Good luck.

 

I just posted this thread.

It may or may not help others.

https://www.corvetteforum.com/forums...post1593656974

DUB