: Update on my'68 with more problems

07-15-11, 12:56 AM
My'68 convertible that I had a previous post on has a new problem. I rebuilt the carb, Quadrajet. Totally cleaned it out, put back together no problems. It looked great, started right up. Still had a little stumble but way better than before. Took it for a test drive. Went a couple miles drove good,took it up to about 50 a couple times it stumbled a little but not too bad. As I was a block from the house started running on about 5 cyl. Opened the hood and the carb was boiling fuel. Intake at the spot on driver side was white hot. I let it sit for about 20 min and fired it up still ran like crap. Haven't pulled plugs yet. Why would it boil the fuel in carb and get so hot?

Any ideas? Mike

07-15-11, 02:00 AM
If the ignition components are in good condition, I'd go back to the carb.

07-15-11, 02:14 AM
Pulled the plugs little bit ago. They are running a little lean, kinda off white. One wasn't firing properly, that was my stumble. They are Autolites 64. Btw. The ignition is Pertronix. Seems to be working. One stupid thing I have noticed, I know I set the timing to 8 degrees and locked it down. I had only drove it about 10 miles last weekend and parked it until today, when the timing was 25 degrees. Reset back to 8 today then I drove it. It had power it seems. Guess I'll try again tomorrow.

07-15-11, 11:40 AM
Go with some AC Delco plugs. Are you disconnecting the vacuum advance when you check the timing?

07-15-11, 01:10 PM
Ok i'll try the plugs. Yes on taking vacuum hose off, I did notice that there isn't much off a difference when the hose is off tho. There is vacuum at carb. The othere thing i'm curious about is the AIR system on that motor. I had the ends of heads plugged off so the sytem is not being used. With that off of there is it possible thats why its getting hot up in the manifold area? With the gases not being evacuated it just builds up heat, right? It coould easily be put back on, I have everything and the pump is still on the motor, just no hoses hooked up. Mike

07-15-11, 03:27 PM
I still think there is an issue with the EFE valve, or maybe the ductwork under the intake. Cadillac did not always install the valve, but the intake would still have the passages for the exhaust gasses to flow underneath. You say the valve isn't there (did you take it off yourself?), but there may still be an obstruction on that side, causing the exhaust to back feed under the carburettor.

07-15-11, 04:41 PM
You are talking about the valve in the exhaust below the header correct? It was on pass side but it is gone. I was thinking about pulling manifold off and looking in it. I did clean manifold up and didn't see anything blocking in any of the openings in manifold. I'll double check everything. Mike

07-15-11, 06:16 PM
Yeah that's the valve I'm talking about.

You said you have duel exhaust. Do you have two separate pipes that come off the engine and run to the back? Or is there a "Y" pipe somewhere in the middle that splits it and send to the pipe to the other side?

If you have the "Y" pipe set up, then there should be a crossover pipe that takes the exhaust from the passenger side header to the rest of the exhaust on the other side. If the crossover pipe is obstructed, the exhaust will backup and start going under the intake; just like if the EFE valve was there and closed.

If you have true duels (two pipes running from the engine to rear), then if one was obstructed, you would notice a difference in flow that one, especially at cold start. You cant test it by putting you hand next to the end and feeling the pressure and comparing the two pipes. If there is an obstruction in either one of the pipes, at any point, it could cause enough back-pressure to cause the exhaust to flow under the intake. You probably wouldn't notice any drivability issues related to a clogged exhaust, because you have the other pipe and also due to the issues you've been having with the carburettor .

07-27-11, 12:47 AM
Well as of today I put the air pump back in working order. It seems to be running better. I still have the low idle miss. I did rebuild the stock carb (quadrajet) but it's the kinda miss/stumble off idle that is driving me crazy. Mike