Motor Abruptly Won't Idle

[MercuryMarc]

I have been emptying and refilling the gas tank to get my sending unit calibrated. All of he sudden last night after I drove 100 yards my car stalled when I took my foot of the gas. I was able to get it home by restarting the car and keeping the RPMs up by keeing the accelerator depressed even when stopped. I checked the carb and all the vacuum lines look tight and the gasket looks tight. I tightened everything and restarted- same problem- runs at hight RPMs, stalls at low speed. The linkage and idle speed screws look fine.
So I do not think I have a vacuum or linkage problem- I think some gas was contaminated and has plugged the idle circuit.

Before I pull the carb and rebuild it, is there anything else I should do first? Is there a was to clean the circuit wih the carb still mounted?

It's a HW5200 on a 250I6.

Thanks!

 

[JackFish]

Maybe the fuel pump died.

 

[MercuryMarc]

Thanks for the suggestion- I believe the fuel pump is fine.
I removed the carb and replaced it with my 1V Holley 1940- car runs great now. So there must be a prob with the carb. I was able to get it running with the HW 5200 and the choke closed, and then increased the idle to 1100 rpm and turned the choke off. Seemed to smooth out with my hand over the barrel so I suspect a vacuum leak- but I checked all over with a hose to my ear and could not find it. So all of the sudden I developed a vacuum leak or I have a plugged idle circuit (my best guesses). So....I'll drive for a while with the trusty 1V and rebuild (again) the old 2 barrel.
Thanks-

 

[rickwrench]

I have a 6" peice of 2" pipe that I use to do the occasional "vacuum tune-up" on the 1946. I dipped both ends of the pipe in tool dip, for safety...
What you do is set the pipe on the carb air horn in place of the air cleaner. Start the engine (or have someone start it for you) rev the engine up to about 4500rpm and smack your hand down on the top of the pipe. FOOMP! your hand will be glued to the pipe from suction, and -any- tiny bit of crud stuck in the jets will be sucked free. A few revvvvvvvv!!!!!/FOOOMPs and the carb will be completely free of any spec of loose crud. The engine might die a few times, and you should stand off to the side in case of a flaming backfire.
If this doesn't clear the crud, the carb needs a total rebuild.
For a 5200, it might work with one hand over the secondary and one smacked over the primary.
Rick