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Bogging Caddy

2K views 16 replies 9 participants last post by  1972Mach1 
#1 ·
So here goes. It is a 71 Cadillac with the original 472 engine. It was brought to my shop because it bogs down on a hard pull. I test drove it and confirmed as soon as the secondaries open it loses power and pings. The car is bone stock and low mileage. Customer installed a new Quadrajet. New fuel pump, new dizzy, new plugs and wires. Checked fuel tank and lines. Nothing helped. He bought it after it had set for years in storage and drove it home. I have checked the ignition timing, fuel tank, fuel lines, tried a new eddy carb, tried an electric fuel pump. Tried moving ignition timing. Nothing helps. The thing bogs down any time you open the secondaries. Even in the shop in neutral punch it to the floor and bam it bogs and pings. No popping or backfiring. Any thoughts???? Thanks!!!
 
#2 ·
How old is the gas? 71 was probably still a decent CR. Bad gas and high CR don't work well together.
 
#3 ·
Does it have the original exhaust on it?
Way back when I ran on the local first-aid squad, we had a Caddy Ambulance with the 472. Apparently in those days the front section of the exhaust was a pipe-inside-a-pipe. One night we drove through a large puddle and the engine cut off as if someone turned the key. Would crank but not restart. The shop found that the inner pipe collapsed on itself, blocking exhaust flow. Just a shot in the dark.
 
#4 ·
Yes. My dad used to run into that a lot at his shop back in the 70's. I think it was happening on Chrysler and GM cars at the time. It would be easy enough to do a quick test by just loosening the pipes right at the manifolds to give it a leak. Then see what happens when you open the secondary.
 
#6 ·
Exhaust is original with exception of the muffler. We did take muffler loss, but not the pipe to manifolds. I did notice exhaust flow falls off tremendously when secondaries open. (I held my hand next to tailpipe as a helper accelerated the engine.) I have heard of the double walled pipes of the 70s but was not aware this might be one of those cars..... I think I will try loosening the pipes at the manifolds.... Thanks again!
 
#7 ·
Maybe the secondaries are jetted wrong, so it leans out or is too rich? I wouldn't think a new carb would be like that, but maybe.
 
#8 ·
Make sure that the hanger is moving at the back of the carb, between the secondaries, when the throttle is floored. There's a plastic cam in there that rotates and operates the secondary metering rods (which are hooked to the hanger). Also, you can adjust how fast the secondary air door opens. They may be opening too fast (see youtube vid). Are the squirters squirting when you floor it (accelerator pump)?

 
#14 ·
What about checking the timing chain? Caddy engines were kind of known for having timing chain troubles. Maybe it has jumped a tooth or two and someone in the past reset the ignition timing after that happened. You might want to take a wrench and rock the crank back and forth to try to feel how much slack there is in the chain. If it seems excessive pull off a valve cover and check cylinder number one for split overlap. Turn the engine by hand until both valves are open the same amount just using a straight edge across the retainers. That event should happen right at or very close to TDC.
 
#17 · (Edited)
I just thought of something.....on my 70 Deville, I'm converting to a pertronix kit. Previously I had tried to put a msd blaster 2 that I know works fine on it. The car would bog and fall on its face with the blaster 2 coil, so I put the stock one back on. Now that I'm doing the pertronix kit, in the instructions it mentions a ballast resistor system not working with my new flame thrower coil. So I check it and sure enough, 6.7 volts getting to the coil. So I'm running my own 12 volt key on power for the new coil. I'm sure this is what was causing my issue with my blaster 2. So if you have an aftermarket coil and its still a system with a resistor, this may be the problem.....hope that helps.

Lucas
 
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