'68 Catalina: Stalls when hot

stalls

#1

I just rebuilt the carburetor. She runs really well when cold & warming up after the choke opens, idles very evenly at low RPM, coming to stops, etc. But when the motor gets hot she idles horribly & stalls coming to a stop. What should I chase after… the mixture, the dwell?



The carburetor service was basic: I cleaned out the various fuel, vacuum & air circuits (chased out lots of crud), put in new gaskets (eliminating some internal air leaks) & installed a new accelerator pump. I didn’t replace the float or change its level. It’s a vintage (original!) Rochester 2-barrel G-series on a 400 ci V8.




#2

The base idle speed may be low. Check the dashpot if you have one. See if the vacuum advance is working. Make sure the choke is opening. Hook up all the vacuum lines.


#3

I don’t know if the vacuum advance is working - it had apparently been disconnected for quite some time w/ its vacuum line screwed shut (heh, a hint…). If the vacuum advance diaphragm holds vacuum is that enough to assume it’s working?

It ran well with everything tuned warm, but coming to a stop in hot idle, it stalls.

This morning it was running cold @ 1500+ rpm in driveway, it dumped crud out the tail pipe & backfired on a restart (unburnt fuel).

It doesn’t have dashpot.

Other things I’m thinking of checking:

It’s missing the idle stop solenoid - it’s in a box, need to test it.

I haven’t checked the PCV or Hot air riser valves.

I haven’t tuned the carb to max manifold pressure.

The good:
It pumps fuel OK, I can see gas vapors when motor is OFF and WARM.

Base idle screw (on the graduated cam) was set to an acceptable idle.

Choke opens when manifold warm (pull-off & auto choke OK)

Vacuum lines are new (although a bit long … ).

My mechanic rebuilt the bottom half of the motor & attempted a quick rebuild of the carb (but the venturi base gasket was off by 1/32"). He installed a new timing chain (along w/ new cam bearings, new main bearing, new main seal…). So I think he checked the timing.

I totally rebuilt the brake system but didn’t test the booster – it’s really stiff when motor is off, I figure it should hold vacuum.

Vacuum fitting to transmission was cracked, new hose fixed rough shifting.

Thanks in advance!

/lee