Engine running rough

[Robertw]

I have a 1965 Cadillac DeVille Convertible with a 429 Motor. When the weather is  hot it is starting to run very rough ,backfiring and stalling etc.
Any ideas on where to start .I have had the carby done plugs and points.
Thank You
Robert

[Bruce Reynolds]

G'day Robert,

Could be a couple of things.
(1)   Too lean if backfiring through the carby.
(2)   Too rich if backfiring out the exhaust.
(3)   Timing out.   (Too far advanced)   You did time the engine with the Vacuum off the Distributor, and Plugged?
(4)   Do you know if the Nylon toothed factory Cam Gear has been replaced?
(5)   Bad Coil?   Plug Leads? (Are these Carbon leads)
(6)   Choked up exhaust system?
(7)   Too much carbon build-up in the combustion chamber.

Has the engine been apart?

Have you performed a dry and wet Compression Test?

Could be anything, but a good Tuning Analyser might help.

Bruce.

[Robertw]

Hello Bruce,
Thank you for your help. It can be never ending trying to find these things.
regards
Robert

[Bruce Reynolds]

Robert,

How are you going with the issue?

I have another thought that I forgot about when dealing with a similar problem.

The car had so much rust inside the Muffler, that occasionally, a flap of rusted internal tin from the muffler would flip up and cover the exhaust pipe, thereby blocking the exhaust.   When the engine stalled, the piece would fall away, and the car would start right up, till it happened again.

Took a long time to locate that one.

Bruce.

[Robertw]

Hello Bruce,
Thank you for that .I will check it out.
regards
Robert

[Robertw]

Hello Bruce,
Do you think the trouble might be the timing chain. It has never been changed and the car has done 94,000 miles. The things that are happening say it could be that.
Regards
Robert

[Bruce Reynolds]

G'day Robert,

Anything is possible, but an erratic timing caused by a cam gear that is falling to pieces is a possibility.

The best way for checking for a loose or stretched timing chain is to take off the distributor cap, and with a wrench on the front of the crankshaft, turn the crank one way, till the distributor rotor moves, then turn the crank the opposite way till the rotor cap moves in the other direction.

A good timing chain will start to turn the Rotor as soon as any slack in the chain has been taken up, maybe a couple of degrees of the crankshaft movement.   If there is a lot more than that, then I would be suspecting the chain or gears.

Not sure if it is possible to see down through the distributor shaft hole if one can see any part of the timing chain, as with the front-mounted distributor, you might even see it using one of those bore scopes.

Also not sure when Cadillac started to use the plastic covering on the cam gear, but if they did, you might be surprised what you find.

If there is nothing wrong there, I would be looking elsewhere.   Have you fitted a Vacuum Gauge to see what the Vacuum signal is doing.   There are charts that show what the various readings mean.

Bruce.

[Robertw]

Hello Bruce,
Thank you for the email. I have the car booked into the mechanic next week, so we will do all the things you mentioned. Hopefully we will find something.
Regards
Robert