Hey guys, I am having a lot of trouble getting my new motor running smoothly. I just installed a rebuilt 468 bbc that I purchased from a friend who had it rebuilt at a local reputable machine shop. Here is what I know about the motor:

'79 454 2bolt truck block - .060 over
781 oval heads - unknown valve size or cc
flat top hyper pistons
stock refinished rods & crank
stock replacement camshaft
summit aluminum dual plan intake
ac delco r43ts plugs

I guess I don't know that much about it, but I had the pan off and everything looked brand new with assembly lube all over. I just purchased a new MSD street fire HEI distributor and holley 750cfm vacuum secondary carb from summit. I have a holley black electric fuel pump and a holley regulator with a gauge, the fuel pressure is solid between 6-6.5psi.

Anyhow, the problem is that it will not idle at all, and above around 2500rpm it seems like there is a rev limiter, I start having a misfire on different cylinders. I can't trace it down to any one cylinder. It seemed like when I started it the first time, it ran pretty good, however the longer it runs the worse it gets. It ran good enough at first where I was able to break the cam in and run it at varying rpms for about 20 minutes. However, now it will not even get close to an idle. If I don't have the base ignition timing advance cranked up, it will also die (which I can't really set because it won't idle).

I tried a known good working edelbrock 600cfm carb and it seemed to run a little better, but it still had very similar symptoms. It just seems to misfire on varying cylinders like it is a bad ignition module, but I took it out and had it checked. I have quadruple checked my spark plug routing and I installed the distributor with the rotor pointing to #1 on cyl#1 at TDC (visually confirmed with the valve cover off).

This is driving me crazy! If anyone has any helpful tips, it is appreciated.



http://boggsman.com/photos/images/the_nova/big_block_time/mini-dscn1034.JPG
Just so you know, this is an old pic, I changed the carb and spark plug wire routing since

Is that a fuel pressure regulator in the photo? If so, is that needed on a basically stock combo? Seems like an unnecessary variable. Have you pulled a valve cover and inspected the valves/rockers/springs?

Since you say its a stock replacement cam, I'd assume it hydraulic. I'd run the valves again and use one of the attached methods. (I use the 'crane cams' method) If they were too tight they could possibly keep the valves open when the engine heats up.

http://www.centuryperformance.com/adjusting-valve-lash-spg-149.html

http://www.cranecams.com/?show=techarticle&id=2

yep , adjust the valves again !

Georgia69, It is a holley "black" electric pump. It said that it needed a regulator. I just got the pump so that I would have plenty of room in the future. I guess I could try a different pump, but the gauge says the pressure is ok?


bradley, you may be on to something. It is a hydraulic cam. I did take the valve covers off to make sure all the rocker arms were moving and it seemed like they were. I have not checked the valve lash though. I will definately take a look at that soon.

Thanks guys!

The first time I built a big block, I over-tightened the valves. It's an easy mistake to make. Mine wouldn't run at all though, until I corrected it.

What motor was in the car before?

yep , adjust the valves again !

x3, adjust the valves.

check for vacuum leaks.
spray the edges of the intake, all fittings, base of carb, throttle shaft of carb, double check all hoses....

OH, if that picture is recent, get the ground wire on the electric choke....your choke won't open....will play hell with your engine tuning....

before you go any further i would just loosen every valve a half turn and then start it. If the idle gets better and misfires lessen then you found your promblem. valves are likely to be to tight been there done that a few times

Thanks for all your help guys, I will definately take a look at the valve lash. It will be Wed or Friday before I can take a close look. I will let you know how it goes.

Put a vacuum gauge on it first. If the needle isn't steady, you need to adjust the valves. Otherwise if the needle IS steady, the problem lies elsewhere. The vacuum gauge method will save you the hassle of pulling the valve covers off for nothing.

Check your float level and make sure the choke is opening too. X100 on the valve adjustment.

Remember me? I FINALLY got the thing running decent enough to putt around the driveway.

You guys will not believe what the problem was, it ended up being the ALTERNATOR. I had a feeling that it was somehow ignition relation, but since I tried 3 different distributors including a brand new MSD one, I ruled that out. For some reason with the alt connected, I kept blowing up hei modules. I got a new alt and the problem went away. Really strange.

Here is a video of me putting around the driveway. It still needs some tuning obviously, but I was excited I just wanted the car to move on its own for once in a long time.

YouTube - nova 454 ss avi


Thanks for all your help guys!

From the sound of that video seems the timing is REAL slow.

From the sound of that video seems the timing is REAL slow.


it probably is, i hadn't set it with a light yet, i had the distributor in and out 10 times already and was just happy it was running that good. i still have a lot of tuning to do.

I really appreciate tips any way I can get them though.

Was the cam broken in properly? Did you put additive in the oil so the cam would live? did you run it at 2000 to 2500 rpm for a half hour or so when you first started it? If not the cam could be wiped out