Stumble with rebuilt Thermoquad /340

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lucahemi

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Original 1972 Demon /340 factory Thermoquad. Rebuilt by Carburetors Unlimited.
Fresh Engine / Revenator and New Distributor. X heads / Comp Xe 268 Cam / 10-1 Compression/ TTI Headers / 4 Speed.
Need help with sorting out the Carb. Car seems to be running lean based on plugs.
In 1st gear car will fall on its face when you nail it. Timing initial 18 degrees all in 34-35.

The speed shop blocked the heat riser on the stock manifold thus choke is not hooked up.
Who can point me in the direction to fix before I purchase a new Holley. I have heard great things about the T-Quad but am missing the surgeon to get dialed in??
 
Does it squirt gas into the primary side and the first instant you move the throttle linkage??
 
^^^ this as said above....it this is not Ok....... try adjusting to the next hole on the pump arm....also, another possible problem is to check with engine idling tap on the secondary plate and it should rock about 1/8 inch or so back and forth....If there is no play in it, that is your problem....need to bend the linkage to create a little slack in the secondary plate....also if plugs are lean need to fatten it up by adjusting screws outward 1/2 turn at a time
 
There is no way in the world a Thermoquad can be adjusted to run perfectly without being on a running engine where it can be adjusted for that particular engine. And I mean NO WAY. It's the luck of the draw if you buy one or have one built and it bolts on and runs good.

Here is what "I" would check first from what you describe.

Remove the air cleaner. Start the engine and warm it up. Take your finger and very gently try to push the secondary air door open.

If you can push it open any at all very easily and then it gets hard to push open, the secondary dashpot control rod needs to be bent so that that "slack" is removed.

You should not be able to push the secondary air door open AT ALL with the engine running without IMMEDIATELY fighting against the secondary pulloff. Don't go too far and tighten it up too much. Just bend the rod JUST enough so the slack is taken out.

Check that BEFORE making a change to the secondary air door spring tension. Usually, that's what's wrong.

If the air door is tightly pulled closed when running and there is no free slack, then you probably need to adjust the secondary air door spring tighter.

Check on the slack first and report back.
 
Lucahemi, the TQ has a lot of little things to contend with and look after. The slightest adjustments effect the carbs running and operation. RustyRatRod can take care of you on this. Just take your time, a step at a time.

The heat riser for the choke operation hampers the carbs cold running effort. A fully warmed up engine is a must without the choke operating. With the engine/carb running under temp, it will be cranky and a pain.
 
lucahemi said:
The speed shop blocked the heat riser on the stock manifold thus choke is not hooked up.
Click to expand...

These are not mutually exclusive. I assume you mean the Heat Crossover under the carb, is blocked,and that the choke linkage has been removed or otherwise disabled.
The heat riser is a valve in the factory exhaust manifold.

So what have you installed under this TQ? The 340 from the 72Demon? or is the carb off a 72 Demon 340? Or is it a Hemi? Is it a 3.31 stroke ? or other? Does it even matter? At this exact moment;no. But in a few more questions it may be useful information.
 
Guys thanks for all the input!!!!!!! .
I appreciate the car guys helping another car guy out. I need to do the advised homework and will let everyone know. Carb is going on the same 340 it left the factory with. Yes the choke is disconected.
If I get this carb sorted out I will pull the manifold and get the choke back hooked up.
Glen
 
You say the choke is not hooked up. Does it have the choke pull off on it? If that has been left off, there is your problem. The choke pull off also acts as a vacuum brake for the secondary air door. If it or any of its associated linkage is missing, that could very well be what's wrong.
 
RustyRatRod said:
You say the choke is not hooked up. Does it have the choke pull off on it? If that has been left off, there is your problem. The choke pull off also acts as a vacuum brake for the secondary air door. It it or any of its associated linkage is missing, that could very well be what's wrong.
Click to expand...

RRR is right on here.........Without a doubt, this is the MOST common problem for a TQ that bogs that I have personally seen. I have even seen guys remove the vaccum pod and really tighten air door to compensate. Then they wonder why it bogs AND runs rich at WOT.
 
Carb is a 6138S . I do not have a fast idle solenoid mounted on the carb. Most of the literature shows. Should this carb have one?

Yes the choke rod is completely disconnected from the carb .
I used a cable tie to keep the door on the primarys open.
 
lucahemi said:
Carb is a 6138S . I do not have a fast idle solenoid mounted on the carb. Most of the literature shows. Should this carb have one?

Yes the choke rod is completely disconnected from the carb .
I used a cable tie to keep the door on the primarys open.
Click to expand...

Post a picture of your carb. The fast idle solenoid has nothing to do with your bog issue
 
For some reason files will not load.
This will soon be the first 72 Demon with a 4th generation Prius drive train!!!!!!!!!!!!
 
Is the fuel in your area E10 or similar with ethenol mixed in with the gas? There are several things that I had to do to help out a similar problem with my 78 318 truck.

The biggest difference came when I read that with ethanol you must increase the primary jet size by two. In other words, if your carb normally came with #98 jets, go to #100 or maybe #101 jets. Jets and #1966 metering rods are still available from places like Quadrajetparts.com. (Yes I know, the name, but the site also sells parts for other carbs as well.) Pick up a spare junker TQ and remove the accelerator squirter assembly and enlarge the holes to .032 if they have not already been enlarged. Install this onto your TQ.

Different metering rod step up piston springs are very difficult to come by. Junker TQ carbs are pretty much the only source for these. A longer stronger spring will lift the metering rods out of the jets quicker, but will also really affect your fuel mileage.

Another part that is often overlooked is the electric choke assist module. If it is bad, you will have a hard time getting things right. The older ones are sometimes available on ebay. The newer ones still seem to be available at O'Reilly's auto parts as a special order. This choke assist will help to gradually open the choke. Mine was found to be shorted and so my choke would go fully open just a minute after I'd turn the engine on.

The off idle stumble drove me nuts until I did these changes to my 318 truck. I'm currently running a Frankensteined 1973 vintage TQ that I bought at an auto swap meet 20 years ago. It is the 1 1/2 primary bore with #100 jets and #1997 metering rods and a drilled out accelerator pump squirter. Because I live in California, my truck has all the smog equipment installed and working.
 
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