What functions as a choke pull off on the Hemi choke system?

[AR67GTX]

Trying to get my Hemi choke system back to functioning properly. It worked fine last winter but is sort of balky in kicking off now. I understand the system pretty well except for one area. What counterbalances the choke system to pull the choke blade fully open as the bimetallic spring heats up from the choke tube and contracts CCW, releasing pressure on the choke link? Is it vacuum pulling down on the little piston that pulls the blade back to fully open by the link?

Mine is tending to hang partly closed after warmup, but I found where I had forgot to plug the distributor vacuum advance hose back in the last time I worked on it, which may have killed part of the vacuum signal. But that’s a ported vacuum source so it doesn’t provide vacuum at idle. Is there a vacuum path in the choke housing that operates on the piston? I know there is a small port with gasket where the housing connects to the carb body. I assume that vacuum port initiates flow through the choke tubes down to the manifold and up to the thermostatic coil area to heat it. But maybe it also actuates the piston thing-a-ma-jig(?).

thanks

 

[Dave6T4]

I am pretty sure that port between the lower carb body and choke housing supplies vacuum only for the choke pull off. Sometimes that little round seal gets hard and leaks.

 

[AR67GTX]

Thanks Dave. I put a new seal on last winter and adjusted everything per the FSM and it seemed to function fine for 6 or 7 months and then didn’t. I pulled the cover off it recently and found some soot inside that I wiped out, put it back together, and slid a sleeve through the manifold in case the tube was rusted out. When I next drove it, it still stayed in the choked position after warming up and I had to manually open it when it was warm. But then I realized I forgot to plug the vacuum advance in.

I guess I need to pull it completely off, clean it up real good and see if maybe the vacuum leak was the issue. I do not have a heat riser valve on the car any longer but that didnt seem to hamper the choke function, just took the car longer to build manifold heat and to smooth out after a cold start.

 

[Dragon Slayer]

Correct that the vacuum of motor pulls piston down against the spring tension of the cap. Index marks on original choke assembly. If you had a heat tube fail, you would get exhaust gas and soot into the choke which would foul the chamber and piston. So piston may not be moving freely. Additionaly, you may have too much spring tension forcing a rich choke condition, and longer to come off. You can rotate to leaner condition (less tension on the choke) to help it come off choke faster.

 

[AR67GTX]

Great - thanks for the clarification. Looks like I just need to disassemble it again and clean it good. And remember to hook up the vacuum hose.

 

[Dragon Slayer]

I guess the bigger issue with the exhaust valve not working is that your not getting exhaust flow through the intake manifold to warm it up faster. Cold weather you would have more liquid fuel in the intake and affect distribution and cylinder mixture. My car is an easy starter when warm and hard starter when cold.