Damn Thermoquads.

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Kern Dog

Kern Dog

Build your car to handle.
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I have a real crappy run of luck with these carburetors.
Every one that I have owned, old or rebuilt seem to give me trouble. The latest is the one in my 73 Dart Sport. It is an original 340 car that I got without an engine. I had a low mile 360 on a stand so I regasketed it and put it in.
The car can sit overnight and be impossible to start. No action from the accelerator pump. The fuel filter has gas clearly visible. I can spritz a quick shot of ether, carb cleaner or even brake cleaner and hit the key and it will start right up and idle fine. I can let it run a minute or so and the accelerator pump works great. An hour later, it starts fine. The next day, it requires another spray of something to start.
This dude runs great! It idles great, sounds nice and smooth. It makes plenty of power with no bogging or hesitation. It just fails to start when cold. I plan to sell this car so I really need it to run right.
This carburetor has been rebuilt by a local guy that I trust. I even took it back once and he got it to work while on the work bench. I am tempted to just buy a new Street Demon based on the ThermoQuad pattern but I'd rather not spend more money on the car.
Anyone have any tips on these carburetors?
 
Kern, I have several Mopars with Thermoquads and have found that in order to get them to start immediately when cold, you would have to set the choke so rich that the engine would load up and die soon after it starts and then be difficult to re-start. Unfortunately you've got to set the choke fairly lean to avoid flooding, which means you're going to have to crank it awhile before it will start. I have never found a way around that.
 
Could be your floats? I read the factory floats are prone to sinking. Brass floats could be a possible solution
 
Ok squirter don't squirt, glass fuel filter is dry................where did the fuel go??????? Downhill, all the way back to the fuel tank.
The Check valve, aka one way valve (in the mechanical fuel pump) is leaking. fuel is sneaking by it and running back into your fuel tank.
Hit it with some carb spray......eng starts, fuel pump pumps, and everything is ok.........

If you have the Carter Super Pump you can take it apart and try and clean the check valve......if it stock factory. Time to try another one!

Its NOT your carbs fault, there is no fuel in it.
 
I have a clear fuel filter up near the carburetor. It has fuel in it and the level has not changed overnight.
To recap:
For the first start of the day, I can crank and crank it over, pump the gas pedal 100 times but it will not start. I get out and spray a 1 second blast of almost anything down the primary throats and it starts and idles great. I may be wrong but my logic tells me that the carburetor has fuel in it, it is just that the accelerator pump is not working until the engine warms up.
I am used to working on Holley carburetors. If you have half an ounce of gas in it, the accelerator pump still works since it is at the bottom of the bowl. Maybe the ThermoQuad requires a higher fuel level to spill over into the "well" for the accelerator pump? Maybe ?
 
electric pump...bam! A mechanical will pull right through an electric if you dont want to keep it on. My B2000 has a one way valve on the return line and a one way electric pump on the supply side (I tried to blow fuel back with an air compressor, the Facet style pump check valve is air tight) , but the fuel can't be siphoning out of the bowls as they are vented and the fuel level is below the inlet....Check your main well plugs. I bet they are leaking your fuel bowls dry overnight.
OR...your pump is shot but that would create a huge lean bog on acceleration. Disconnect pump rod linkage one night and manually cycle the pump in the morning to feel for any drag on it. A Limp pump would tell you if there was any fuel in the bowls. Fuel would be leaking into plenum if they were dry, and your oil would reek of gas. They don't boil dry like an AFB. The way the TQ Accelerator pump works is like a bucket: It fills from the top and pumps out of a tube at the bottom. If your float levels are low or you are losing fuel overnight, the "spillway" is under the fuel level now and it will go dry with 1 shot or less. Check here Offroad Exchange - Carter Thermo-Quad Rebuild and look at pic of accelerator pump design.
Pic07.jpg
 
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Keen dog, the internal plastic straw that feeds the squirters from the pump shot gas well, is it cracked?
And as pictured above, the jet well(s), are they good as well.

Choke setting, as speced? Choke we'll choke or electric choke? IF it is a choke well, is it adjustable? Or is it just a bi-metal spring? A little bit of a rich sett My isn't so bad.

These things need to be exact. And it is a huge pain from time to time.
 
The choke is not hooked up. I am used to Holley Carburetors and since I rarely drive these cars when it is 50 degrees or colder, I haven't needed a choke.
Is it fair to guess that this carburetor needs an operational choke to run right on a "cold" start even if is not technically cold outside?
 
Pisha wrote.....
" The way the TQ Accelerator pump works is like a bucket: It fills from the top and pumps out of a tube at the bottom. If your float levels are low or you are losing fuel overnight, the "spillway" is under the fuel level now and it will go dry with 1 shot or less."

Now THAT makes sense. Maybe something as simple as a float adjustment?
 
Kern Dog said:
The choke is not hooked up. I am used to Holley Carburetors and since I rarely drive these cars when it is 50 degrees or colder, I haven't needed a choke.
Is it fair to guess that this carburetor needs an operational choke to run right on a "cold" start even if is not technically cold outside?
Click to expand...

Choke is needed with a Thermoquad. Mine won't start without it.
 
So go out first thing in the morning, pull the air cleaner, look down the throttle bores with a light, and pump the throttle 3 times, see if there's anything being pumped. If nothing comes out either there's not enough fuel in the in the carb or the pump material has contracted.
 
I don't know what you're doing wrong. But a properly adjusted TQ starts faster than fuel injection. Connect the choke. Step ONCE on the accelerator, turn key, it should fire right off.
 
LMFAO...thats why we took them off and threw them in the trash..garbage plastic carb.
 
Daves69 said:
If nothing comes out either there's not enough fuel in the in the carb or the pump material has contracted.
Click to expand...
I had to replace the accelerator pump in my TQ with one that is more ethanol friendly because the old leather pump material contracted enough to not get a proper squirt.
 
I've rebuilt at least a 100 of them. I've had good luck with them. Just rebuilt one last week for a 71 340 Shaker Challenger. I once bought a TQ at a swap meet, where someone had put all four external links in the wrong place, and tried bending them to fit!
I have not been into the "new" Street Demon, yet, but it looks like they did away with some of the best features of the solid fuel TQ's.
 
I ve had that problem with a rebuilt one about 25yrs ago , there are two O rings in the bottom of the bowl where the main boosters pick up fuel , the rebuilder forgot to put them in (they are hard to see , black rubber over black plastic bowl) and fuel leaked in the plenum slowly...
 
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