‘59 Cadillac Fleetwood Sixty Special - Carter Carb Issue

[Fleetguy]

Morning all!

I am coming to you all with a carburetor issue that we are experiencing after a rebuild. About a month ago we had the original Carter AFB rebuilt on a 1959 Cadillac Fleetwood Sixty Special. Previously it ran quite smooth, but the accelerator pump was worn out. So, we decided to have it rebuilt.

After getting the carb back, we reinstalled with a new spacer, gaskets, and tin plate. We placed all the items in the same manner that the shop manual explains. Upon hooking everything back up we cannot get the car to idle well at all in gear. In park it is decently smooth. In drive the car is rough and also smokes (more like grey smoke). It never smoked with the old carburetor installed.

We went through the exact running procedure in the shop manual after the car has warmed up and is off the fast idle. The idle mixture screws do not seem to change the vacuum whatsoever, but the center screw will provide a different RPM. If you cover up the primaries at the top the car will stumble and die. So, I guess I cannot imagine it is a vacuum leak.

Any thoughts on why the idle mixture screws would not do anything once the fast idle is off? Thanks so much for any thoughts you might have. I found similar issues on this forum, but never any responses on what the solution was.

[Dave Shepherd]

Spray carb cleaner or propane around the base of the carb, see if there is a change in engine speed, if so, vacuum leak. Also make sure the secondaries  are fully seated closed.

[Fleetguy]

Dave, I have sprayed around the base for any leaks and came up with nothing. It didn't idle up at all doing that.

Is there an easy way to tell if the secondaries are hanging open slightly at idle, without taking the carb off? Thanks!

[Dave Shepherd]

Yes, spray propane right into the secondaries.  Also  make sure you have the right base gaskets, possible they are blocking an idle bleed port.

[fishnjim]

sauce for that goose.
Next time post the carb number so we know if it's the right one or not.
Have fun.

[Lexi]

I think I got a core Rochester '59 carb, or two, if you want to swap carbs. One of them has the idle speed up control unit on it. Also have a single 4 bbl intake manifold for a '59, if you are stuck. Clay/Lexi

[Fleetguy]

Yes, spray propane right into the secondaries.  Also  make sure you have the right base gaskets, possible they are blocking an idle bleed port.

Dave, I think this is a good thought. We just looked and the original gasket is different than what was sent to us.

This is what is on there:  https://www.ebay.com/itm/224224225365

This was the style of the old gasket:
https://www.ebay.com/itm/223992258854

If these eBay ads are labeled correctly, would these gasket differences cause the issue?

[Dave Shepherd]

If you used the Rochester gasket, this will not work. The Carter looks right, but it must match your old one.