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1969 convertible
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25 Posts
Discussion Starter #1
Hope you can help with an recent issue on my 69 Caddy DeVille. It starts fine and idles fine, for a while, then stumbles as if it will stall, but it doesn't. Then it goes back to idling fine. The stumbling is erratic and lasts from 5 seconds to a minute or so. Punching the gas sometimes makes it stop stumbling. It accelerates ok, except when it is stumbling, then acceleration stumbles as well. If not stumbling, it runs and accelerates great. Seems electrical to me, but maybe fuel. The original fuel pump has a nice ticking sound. Suggestions?

Other information:
stock engine except for pertronics III & flamethrower coil (powered by 12v, not the resistor wire)
rebuilt original 472 engine with 2000 miles on it, issue just started
original distributer
original fuel pump
vacuum on intake manifold at idle is 20
new plugs, wires, distributor cap, and rotor
rebuilt original carburetor
 

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1996 Eldorado
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2,814 Posts
The electronic module may not be tolerating play in the old distributor shaft, pull the cap & check for shaft play in all directions.
If its rubbing the pick up, that will kill the module or the opposite is happening and the pick has too much gap from the loose shaft bearings and not getting a proper signal.

The bottom of the dist. shaft usually wears more than the top so its best to pull the whole distributor & re-bush it or replace if you find slop at the top.

Or a float valve may not seating properly. Do you smell Fuel?

If the float valve is not seating leaking it may cause a brief stumble til it burns the excess fuel or a piece of crud it may be actually flooding a bit at Idle and you would smell raw fuel and it would idle like crap, emit black smoke.

I don't know if the fuel pump could be weak, you only need about 4 PSI to keep a Quadrajet full of gas at any rpm.

I can't think of any good reason to run the 43 yr old diaphragm fuel pump fresh motor. If its ticking thats a big problem, it could take out the pump cam.

The filter at the carb could be restricted or muck in the tank could be restricting the screen at the tank pick-up.
 

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1969 convertible
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25 Posts
Discussion Starter #3
I'll check the distributor. I don't remember a lot of play though, but it is the original. This issue just started after I put in the pertronics/coil/wires. It seems to only stumble/rough idle intermittently when the engine is warmed up. I put a timing light on each of the 8 wires and it looks like 3 of them right next to each other on the cap are getting intermittent spark during the stumbling/rough idle, which leads me to a bad pertronix unit or a worn distributor.

The fuel pump ticking/tapping is constant, and when listening to it with a mechanics stethescope, the ticking lessens or goes away briefly during the stumbling. I was thinking of putting in a new one anyway. The prior owner is the one who had the engine rebuilt, and did not replace or rebuild the fuel pump, carburetor, or distributor.

Concerning a stuck float, perhaps, but it is odd that the stumbling/rough idle just start the same time I put in the pertronix. Also, it was rebuilt about 100 miles ago and has worked fine. There was no black smoke. With the engine off, I do smell gas from the snorkle, but I think this is normal and comes from the vent.

Thanks!
 

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1969 convertible
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25 Posts
Discussion Starter #4
ok, answer is? I was using copper strand ignition wires. You can't use them with pertronix. Says so right in the instructions. Duh...........
 

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1970/1991/2005
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52 Posts
Hi I think you Might Have a Fuel Line Leak Check the three Lines Just off the Gas Tank Manual Fuel Pump Filter on Engine .I know It Drove Me NUTS On My 1970 coupe deville My line were Cracked and would suck Air when I got on Her.
 
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