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Thermo Quad Secondary Throttle Inactive. Ralph 8-25-02  
1978 Dodge 440 MH with origonal Thermo Quad carburetor. Having finally fixed a missfiring problem caused by a bad ground, I took it for a test run and the secondary air flap stayed closed even when struggling up hill. Suspect the choke is not coming off fully allowing the secondary linkage to drop and engage the primary linkage. The diaphragm at the back of the carb: seems to be OK. Does this make sense and will there be any surprises when I attempt to change the choke which is hidden under a rusty metal cover?
Re: Thermo Quad Secondary Throttle Inactive. Joe 8-26-02  
Ralph, It is an easy thing to check without getting into the choke yet. Remove the air cleaner after the engine is hot to see if the choke is open if not then prop open the choke manually and see if the secondaries open. The linkage could be rusted up and not allowing the carb to work properly. By the way, glad to hear the grounding cured your problem.
Re: Thermo Quad Secondary Throttle Inactive. Ralph 8-26-02  
Joe, Thanks for the reply. Did what you suggested, the linkages work fine but the choke is moving very little when hot and as a result the secondary linkage is not engaging. Will check the choke which is presumably a hot air type. I think I will also re-kit the carb at the same time as there are signs of leakage and it is 22 years old. Any helpfull tips? Thanks again, Ralph.
Re: Thermo Quad Secondary Throttle Inactive. Joe 8-26-02  
The choke gets it's heat from the manifold crossover. Sometimes the crossover becomes plugged with carbon or the heat riser gets stuck in the open position and in either case the intake manifold doesn't get hot enough to open the choke fully. You may want to check those things first before you go buy a bag full of parts.
Re: Thermo Quad Secondary Throttle Inactive. Ralph 8-27-02  
Joe, To save me time how do I get to the crossover you refer to and where is the heat riser that may be jammed? Thanks, Ralph
Re: Thermo Quad Secondary Throttle Inactive. Joe 8-27-02  
The heat riser is at the lower portion of the exhaust manifold before the exhaust pipe. The crossover is in the intake manifold and is not accessible without removing the intake. Check the heat riser first. Does the choke open at all?
Re: Thermo Quad Secondary Throttle Inactive. Dick 9-12-02  
A thermoquad that is this old needs a lot of things:

1) Rebuild it since....
a) little o-rings in base are prob. shot and you run rich or get hard start when hot
b) If the accel. pump is still squirting OK and no stumble is happening, I'd be surprised
c) foam floats are heavy, THROW AWAY, replace them with brass
d) the float bowls are sure to be dirty
e) you can adjust the secondary unloader spring and get it just right.

2) Put a hand choke on the beast and pitch the divorced choke that always unloads early or late......Dodge went through 3 styles, some with electric assist, and never got it right on carter carbs., also the length adjustment is always trial and error

Trust me, you will pick up better MPG and power and launch characteristics.
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