Vacuum or distributor problems

Z

Zfan

Member
I have a 385 sbc that I have had some issues getting the intake sealed up, finally did get that problem solved but it still acts like it has a vacuum leak. I pulled the intake again only to find it was sealed tight. I put it back together and the same problem persists. I cannot tune the carb or set the timing, If I play with the distributor (msd) it goes from 8 initial to 20 plus and rpm's run up from 500 to 1400, when I try to get the carb dialed in it will either run at 500 or 1400 and not much at all in between.

I have checked the manifold for cracks, swapped a demon 825 carb that ran perfect on my buddy's car only to have it work like crap on mine with zero tunability. I must admit I am at my wits end with this motor. I have had the intake off 4 times now with the same problem, intake is sealed and my carb works fine on other cars just not mine. Could the MSD distributor be bad, I had it rebuilt 1.5 yrs ago. I have replaced the gear and that's about it except for a cap and rotor. I have checked and even replaced all hoses as well.

Anyone got any brite idea's before I take a gallon of gas and a match to it?
 
ideas?

if you've had the heads angle milled the intake gasket might seal on the upper edge but not in the lifter gallery area.

why not try a DIFFERENT distributor temporarily as a test,then if no change a different intake, ( source,friend?, salvage yard?) and /or a different intake gasket that's thicker if you suspect the current ones might be defective.
as always the isolate and test route will determine the problem
 
Block is zero decked, AFR 210 heads milled .010, intake was milled .030, intake bolt holes and heads line up with bolts centered in intake. I had that problem with it not sealing but seems that they are sealing now, I even went from a felpro 1206 to a 1205 for more coverage. Maybe I do need to look at swapping distributors, my friend has a MSD I could borrow I am sure.

If need be I will pull the intake again and mill it more or swap out intakes. This Victor Jr. has been a pain to say the least.
 
step one , verify your getting a good blue spark from the ignition wires and the carb throttle plates open smoothly from closed to fully open without binding, verify your plugs are gapped at .045, and youve got a full 13 volts at the battery, get out your timing light and clearly mark the TDC line on your damper with something bright like white or bright green nail polish, then clean your timing tab so the TDC an 1-12 degree before TDC marks are clearly visible, set the engine at idle then with the timing light watch the spark advance is smooth as you increase the rpms, if it jumps suddenly somethings binding in the distributors advance mechanism, like a weight or spring, rust or crud will do that so clean and very lightly oil it with WD 40 and a Q-tip

some of this info and sub links should help

viewtopic.php?f=4&t=1337&p=2921&hilit=infrared#p2921

http://www.corvette-101.com/vacuum.htm

viewtopic.php?f=50&t=383

viewtopic.php?f=55&t=1639

viewtopic.php?f=55&t=264

viewtopic.php?f=70&t=1411

viewtopic.php?f=70&t=1809

viewtopic.php?f=70&t=232

viewtopic.php?f=62&t=882&p=1390&hilit=+propane#p1390

VenturiVacuum01.jpg
 
Thanks Grumpy,

I will try those steps today when I get home from work. I did clean up the balancer and put fresh marks on it plus put a new timing tab on her also. I will pull the cap and rotor again and do a thurough clean up of the springs and distributor in general.

Thanks for the tips!

Mike
 
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