I just built a 396 Chev engine and during start up, I find it skipping and generally not running good. The carb, dist and other stuff came from a running car but just to make me feel better I changed carbs to another known good one. New plugs (2 nd set) thought I could have fouled one out or something. New wires, etc. It has an HEI dist So here is my question. Where do I look next? Could this be caused by a vacuum leak? How to test for that? I have adjusted the valved again and it got some better but the skip is still there. When you give it some gas it will pop back through the carb a little as well. This is a stock 396 with cast iron heads 1965 model. It has a cast quadrajet intake on it with en Edelbrock carb. The Quadrajet that was on there does the same thing. What is next? What else do I need to look for? THANKS in advance. Mark
Take a compression test and put a vacuum gauge on it. Might see something to point you in the right direction.
Marty I had the same problem on a 427 the outer ring on the bal. had slipped so my timing marks were off, just fixed a buddies 460 ford with the same prob. I have also seen bb chevs with the advance stuck in the hei dizzy. Just my .02... Wayne.......
Thanks, I will get to checking all of these things. I have a spare dizzy and spare balancer, so those things can be sorted out pretty quickly. I do not have a compression tester but probably can rent one. What should the vacuum gauge read? I have one but it is not installed. THANKS for the help. Mark
Go to this site for vacuum gauge readings and their meaning. http://www.earlycuda.org/tech/vacuum2.htm
Retard yor timing and reajust you idle, up. You don't need a timing light just a little at a time. As squirrel said. Any egine will pop thru the carb, on tip in, when timing is to advanced.
A lot of good tips here. Follow the vacuum guage and timing tips, check the balancer. Lastly, if all else fails, check to make sure the timing marks are lined up correctly on the timing chain. Off one tooth will make an engine run exactly as you describe but check the easy stuff first. As far as Vacuum, I've never seen 21 inches of vacuum out of a older V8. I typically see 14 inches with a mild cam, less and less as the duration of the cam goes up. With a lumpy cam I have seen as low as 6 inches at idle. One of the key items you are looking for on a vacuum guage is a steady reading. Regardless of what it makes depending on cam, etc. you should have a fairly steady needle. A bouncing needle wil indicate a sticky valve, low compression, etc.... Scot
To check the mark on dampner to make sure it hasnt slipped it should be directly in line with the key way slot for TDC marking.
You guys are great.....Thanks for all of the help. I will give a report when I get it figured out. THANKS SO MUCH, Mark
No problem, I have seen Dynaflash 8 on here as well. I am sure that you know that Dynaflash is a Buick engine. I think it also sounds a little like a Super Hero.........ha ha
give a look to your intake, adaptor, carb for a vacuum leak. Those setups have given me fits in the past. lots of good suggestions and information has already been offered. good luck.
Base timing set too high will show low vac and you will have a high idle. Too low timing can cause that pop on accel. Find true tdc at the #1 piston and see if balancer mark and timing tab match. peace
If you replaced the cam it's possible you wiped a lobe or just wiped a lobe on an old cam. I did that on my 454. Still ran but ran like crap, popped, wouldn't even out, Nothing helped. Finally noticed that one rocker arm wasn't rocking.
An easy to make certain that the balancer has not spun is to pull all the plugs. I removed the porcelain from an old plug and threaded it for a 9/16 bolt. Then I install the plug in the number 1 cylinder, and gently screw down so that the bolt will stop the piston from reaching TDC. I mark the balancer and rotate the engine backwards until the piston gently touches the bolt again. I mark that point and check to see if both marks are equidistant from the TDC mark on the balancer. If it isn't, then the balancer has spun and will have to be discarded. It hasn't happened to me yet, but a buddy had a spun balancer and it drove him up the wall until I solved the problem.
Probably in the valvetrain,396s are notorious for this.,you said you tightened one down and it improved it some.Check to see if they are all working properly.
OK, lots has happened in my life to make the Big block sit and gather dust, but that story is just too long to tell. ANYWAY, I think I will find some time in the next little while to get back on it. Here is what I know 1) wires are in proper order 2)balancer has not slipped 3) all lifters are pumping oil and all rockers are moving Still need to run a compression test but this is a "new" rebuilt engine. I am beginning to think the issue is in the heads. That one or more valves are sticking or valve ground wrong. I assume the compression test will help me figure that out. I hope to do that tomorrow. I have borrowed an very old compression tester but that is OK it is an old car.
The Jalopy Journal
