Thermoquad rebuild help

[Cuda360]

I recently rebuilt my TQ. This, by the way, was my first carb build. I got it all together, put it back on the car, pour a little gas in, and start it up. It actually idled really well. After letting it idle for a minute or two I tried reving it. RPM went up, but did not go back down. (Now, I occasionally had this issue before the rebuild, but in a much milder form. After a long steady highway ride, I'd come to a light and the idle would be high so I put it in neutral, give it a quick rev and the idle would drop back to normal.) Now if I rev to, say 3000, it would stay there. I can return the idle to normal by pulling the pedal back to its origin. So where did I go wrong, I did not mess with the pedal or its direct linkage.

Another issue is that, upon turning the engine off and sticking my head back under the hood to inspect the throttle linkage, I noticed white smoke coming from the carburetor. What could this be? The engine was only running for 4 minutes at the most. I can't imagine this would be enough time to boil gasoline. Could it be a coating on the new gaskets burning off?

Please help! It is supposed to be near 70 degrees this week and I want to drive!!!

Thanks,
Robert

 

[Juan Veldez]

Well, I try to start with the simplest/easiest things to look at first. I would make sure the return spring is pulling the throttle linkage all the way back after letting off the gas (quick release and gradual release), then that your pedal assembly (including "kick-down" if an automatic) wasn't binding up on something not allowing the linkage to return to full idle, then your vacuum lines are not leaking and attached correctly, then back to the carb to see if the internal parts are operating freely and completely. I would think the smoke is relatively normal after shut down, unless you are talking a lot of smoke. My unprofessional opinions only!

 

[challenger6pak]

I agree with Juan. It sounds like something is hanging up and keeping the throttle open.

 

[Cuda360]

Here's a little something else to consider. The throttle would only stick when I used the pedal. When I went back to the linkage and pulled on the throttle cable to rev it, it would return to idle as normal. :icon_scratch:
The smoke was minimal, but remained for a few minutes after shut down.
I'll double check all of the connections to be safe.
Thanks guys.

 

[Juan Veldez]

Back to my original statement & process of elimination, you seem to have narrowed it down to the pedal assembly binding or hanging up on something IMO. A couple other things I thought about: This isn't a "choke" type issue is it? And when you use the pedal, I assume the hood is up and the air cleaner is on just like when you activate the throttle manually, just making sure we are totally comparing apples to apples, no other variables. If not, anything on the hood hanging down or an aftermarket air cleaner obstructing the action? If no, can you have someone else press the gas pedal while you watch from under the hood? And after it hangs up, try to manually return the carb back to idle at different points along linkage route to try and isolate the exact binding location. I also assume your using a stock pedal and linkage assembly, not an aftermarket cable? Then, I'd say it's time to dive under the dash and look for the culprit there. Let us know.

 

[challenger6pak]

Post a pic of how your linkage is set up.

 

[Cuda360]

I can pull it back to idle by pulling on the return springs. It doesn't seem like a choke issue, but then again, I'm not really experienced with carburetors. And the air cleaner was not on, would that matter? Here are some pictures of the linkage...
Thanks again.

 

[Cuda360]

Here is a picture of the smoke... There is no smoke at all while the engine is running, maybe because the suction is pulling it in? Any clues?

 

[moparleo]

That is just the fuel vapor . You have too many springs and the return spring is attached to the wrong bracket. Try to move the return spring to the bracket the cable is attached to. Remove 2 of the springs on the kick down linkage. Only needs enough tension to move the kick down rod. You have the springs fighting each other right now. Try it and let us know how that works.

 

[moparleo]

Question. It that the correct manifold for the thermo quad ? Looks like the carb mounting studs are too short or the base gasket you are using is incorrect for the manifold.

 

[Cuda360]

Too many springs? Huh? I reattached everything the way it was before I took it off.(But I suppose that may mean it was wrong before.) It is the stock manifold. The base gasket from the rebuild kit was a little thicker but not so much that the carb could not be secured. I'll remove one of the springs and try again tomorrow. My fingers will be crossed until then.
Thanks

 

[VeteranCosmicRocker]

First thing I'd do is throw out all those springs you got on there. Replace with the proper throttle spring & the proper kickdown spring (available from one of the Mopar vendors). You just don't haphazardly throw on as many springs that will fit on the linkage.

 

[moparleo]

Thermo quad linkage

:icon_thumright:Try this

 

[Cuda360]

Success! Thanks moparleo. It started and ran pretty well. That is until I started to adjust the A/F mixture. I noticed gas dripping from the bottom of the carb. Looks like I've got to pull it back off and check my gaskets. Also the car seems to be flooding very easily. Would that require a float adjustment?

 

[moparleo]

Yes Hopefully you got the factory rebuild instructions when you rebuilt the carb. If you did, take your time and go over every adjustment listed in the instructions. I run the Thermoquad on my 340 and it runs excellent. It does require a little extra attention to detail but will reward you with excellent performance and better economy than a Holley.
Also be sure to replace your fuel filter(s) This is required if you want to have trouble free service.

 

[Cuda360]

Well, I've done everything I can think to do and still it is not running as good as it can. So I'm taking it to a local restoration shop this weekend to have them get it perfect. It'll work out well because I also need to get some body work done, might as well do it all at the same time.
Thanks for your help guys...

 

[transman]

Send me a private email to [email protected].
I own a 74 Challenger with a 360 & thermoquad on it.
It's pretty original so I can send you some reference photos if you would like them.
transman

 

[bbrroowwnn]

That is just the fuel vapor . You have too many springs and the return spring is attached to the wrong bracket. Try to move the return spring to the bracket the cable is attached to. Remove 2 of the springs on the kick down linkage. Only needs enough tension to move the kick down rod. You have the springs fighting each other right now. Try it and let us know how that works.

X2....Also, wanted to let you know to check that distributor vacuum advance canister and hose to make sure they are not binding on the kickdown bracket linkage anywhere in the throttle travel.........I always install my distributors with vacuum advance canister on passenger side .....

 

[transman]

Thermoquad rebuild

I own a 74 Challenger with just over 38000 original miles, and it is mostly original.
If you need a photo of the way Chrysler originally put the linkage together, let me know and I'll be happy to pass along to you how it was set up at the factory. I can send you photos.

Now, if you could, would it be possible for you to send me detailed photos of the choke linkage. I rebuilt the carb and didn't take a photo of how the all the linkage and spring is to go back together . I've looked at other Thermoquads, but yours is the first one I've seen that the linkage is the same as mine (my carb is the 6453S). The photos you've posted almost show me what I need, but not quite.
My email is [email protected].

thanks

transman

 

[Big Jim]

Another thing to check is to make sure the throttle cable is not fraying inside the housing- just disconnect the cable from the carb and extend/retract it by hand. Should be smooth and easy. Never hurts to give it a good squirt of lube. Had this happen to my '73 'cuda 340-cable frayed out and hung up throttle wide open...