Working on the 72 454. Hasn't been right since day 1. Replaced the carb., fuel pump, new inline filter (removed carb. body filter), wires, cap, rotor, Petronics conversionon dizzy withnew coil. Good vacuum off the manifold and timing set by ear as setting 8 BTD isn't getting it. Maybe rubber ring timing mark has slipped? Starts right up, idles a little uneven but revs. and runs even holding throttle at different RPM's. When you drive it the car runs fine until at some point it starts missing then dies. Starts right up again and runs until same thing happens. Almost like it's out of fuel or electronic conversion is failing. I have a good 12 guage 12 volt wire powering it right from the fuse block. Resistor wire has been removed. Thin cranking wire is still there. Any ideas? Thanks!

 

Good morning JanS. It's either fuel or spark but I know I don't have to tell you that. Swap the ignition set-up out of your other Vette into the big block, drive it like you have described and see if it makes any difference. The small block and big block use the same distributor so it will drop right in. Only one thought on that is what type of distributor gear are you using in the small block?, stock cam and distributor?

 

77 dizzy will not work as it's a different set up with the cam etc. I was going to go with an HEI setup but the tach. is driven by cable off the dizzy. I went with the Petronics setup and later heard alot of bad stories aboutit.The one in there seems fine, I shimmed it for play and there is no side to side play if you push and pull the rotor. I was thinking of changing it back to points to see if the problem goes away. I'm going to have to look under the car to see if someone put in another fuel filter somewhere inline that might be clogged. The gas tank is clean inside. It was replaced 5 years ago.A worn cam would just run bad period, not come and go. Correct? Thanks!

 

Do you know what type of cam is in the small block, cast iron cam with flat lifters or steel cam with roller lifters? If you can return the ignition system to factory stock with the resistor wire then I would give it a try, at least for testing. A worn cam in the big block won't effect the engine the way you are describing.

 

I think you are hitting on the posssible prob. I'm betting it's in your ignition.
Did you check the settings on your carb?
Float level etc.?

 

Hi Starship. I'm kinda' thinking ignition on this 'cause of the way he describes the problem, but your input is kindly appreciated and it's good to hear from you. I would have suggested some starting fluid to diagnose a fuel starvation issue but he says it starts right up after it stalls-I don't know-just lookin' at one thing at a time.

 

Hi again Jans, you can go to www.ecklers.com/ and look at part # 22921 looks like the key way and the timing mark are lined, up this will confirm that your balancer has not slipped.
Pertronics either work or they are dead, yours works.
Hook up a dwell meter and confirm that the reading is steady from idle to about 3,500 RPM if it is steady than the bearings in the distributor are good.
Take the distributor cap and rotor off and make sure that the springs are not stretched too much and that the weights do not bind or get hung up.
Borrow or buy a dial back timing light and set the timing at idle with the vacuum advance removed and plugged from the vacuum can.
Rev the motor and see if the centrifugal advance works. (Ifthe springs and weights are working the timing will advance).
Now let the motor idle and reconnect the vacuum advance, if your are connected to manifold vacuum the timimg should advance 12 to 16 degrees.
Also if you have a Q-Jet make sure that the inlet filter is not installed backwards.
If all this does give you any improvement than take a look at the sock in the tank it could be clogged.
Hope this helps, PG.

 

Thanks to all that have replied. I'll try and check the carout this weekend. Supposed to get cold and snow here tomorrow but improve on the weekend. I'll let you all know how it goes. Thanks again!

 

O.K., I'm reachin' a bit,...

I have had wires break inside the insulation.
It would get stretched by stress or heat, and break contact. Once the condition changed, it ran fine.
Check your fusable links. I've had them work intermitantly. They don't always burn back far enough to completely break contact.
Do ya have a firewall mounted coil wire resistor? The hot wire that goes from the resistor to the coil may be too tight, and broken internally.
All I can say is, the very thing happened to me.
You get power, or ya don't. There aren't that many wires that could be at fault. Ya just might have to check them over pretty well. If ya find one that stretches, that very well could be the prob.
Check your wire routing to make sure nuthin rubs or gets too hot.