Thermoquad Issues

[Gibber]

I have searched the forum for Thermoquad related issues and this seems to be a new one....I can't seem to get the choke to engage. The fast idle cam will not rotate so that the cam contacts the high speed adjustment screw. The car runs fine once it is warm, although another issue is the idle won't seem to stay set. If I set it per the specs at 900 RPM warm in neutral, once I put the car in drive the idle drops down to 500 or so and the car intermittently stalls. The car is a 71 340 Demon, carb is a 6319 which I researched to show it to be a for a 73 model 340 with auto. The car originally had a Holley, so I purchased this rebuilt carb thru Ebay about a year and a half ago. The choke issue has been since I installed it. The idle issue just cropped up. A couple of pics attached. Appreciate any thoughts on this...

Thanks,

Mark

 

[RustyRatRod]

First off, what the crap is THAT spring? Let's figure that out first. That ain't supposed to be there.

 

[twofosho]

First off, what the crap is THAT spring? Let's figure that out first. That ain't supposed to be there.

Hey Stroker, when are you going to finish the rebuild sticky? I've got a couple Tquads waiting to go in the soup and while I have some rebuild info, I decided to wait to start on them until I had read your thread. Also, do you have a workaround to get timed vacuum for the distributor (drill a new port for it, change out the carburetor baseplate, etc.?) on a Thermoquad (leanburn) that doesn't a port for it in your repertoire?

 

[AdamR]

Mine had a spring there. It was also a 73-340 carb.

 

[RustyRatRod]

I'd like an up close CLEAR shot of that spring if you could please.

 

[AdamR]

I just took mine apart. The spring was smaller then that I believe though. When I pull it all out of the cleaner I will snap a picture.

 

[kt340sport]

I do nor recall ever seeing that spring either, i still have about a dozen of these , and had them , and tried them over and over kit after kit , never to get them adjusted right , what a relief #1406 edelbrock electric choke , change jets and rods for the 340 , way you go.

 

[RustyRatRod]

Hey Stroker, when are you going to finish the rebuild sticky? I've got a couple Tquads waiting to go in the soup and while I have some rebuild info, I decided to wait to start on them until I had read your thread. Also, do you have a workaround to get timed vacuum for the distributor (drill a new port for it, change out the carburetor baseplate, etc.?) on a Thermoquad (leanburn) that doesn't a port for it in your repertoire?

The how to is finished. ....and yes, I am actually working on a jig to drill the main body for the timed vacuum inlet. They ALL have the hole on the inside, but it's not drilled all the way through on some. I'll post when I get it right.

 

[matchlight]

That's a choke modulator spring. It's purpose is to let the vacuum break open the choke faster as the choke spring warms up and relaxes, to prevent overchoking. I think they found that without this, after the initial vacuum break the choke valve would tend to just stay at that same opening throughout warmup, even as much less choking was needed.

You might check to see that the rod from the choke spring up to the choke lever is the right height. That affects the closing pressure on the choke plate. I think the correct spec is 3 3/8" from the base of the carb, sitting on a flat surface, to the top of the hole on the choke lever when you're holding the lever as high as it will go (full choke position). Much easier to check this when the carb's off the car. If you have an insulator under the base of the carb, it will change this measurement.

Sounds like the idle mixture is too lean, if the load of putting the car in gear causes a 400 rpm drop in idle speed. You might blow some carb cleaner through the idle passages to make sure a piece of dirt isn't lodged somewhere and interfering with the flow.

The best info on TQ's I know of is at imperialclub.com. Go to "Literature," then select "Master Technicians' Conference," then go to the TQ information under 1972. There is a film as well as a booklet, explaining just how all the systems work and how to adjust them. The sequence of adjustments is very important. Once these are adjusted right, they are reliable and give a great combination of mileage and performance.

 

[Gibber]

Thanks for the great info...I will first check that choke spring rod height...and then pull the carb and try the cleaning route...

Mark