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ThermoQuad carburetor NO LONGER fails to start when cold....FIXED

Started by Kern Dog, March 29, 2017, 11:12:17 PM

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Kern Dog

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?

c00nhunterjoe

Jsounds like its going dry overnight. Probably boiling or evaporating.

John_Kunkel

Quote from: Kern Dog on March 29, 2017, 11:12:17 PM
The car can sit overnight and be impossible to start. No action from the accelerator pump.

Does the accelerator pump work OK after it's up and running? If not, there's a plastic tube inside the carb that connects the pump to the nozzles; it might have fallen off.

From my limited experience with Thermobogs, they're sensitive to choke operation when cold, if the choke butterfly isn't completely closed when cold it won't start.
Pardon me but my karma just ran over your dogma.

Kern Dog

Thanks, John.
Yes, once warmed up, it runs great. Zero problems. It is responsive and shows no bad habits for a couple of hours after being warmed up. Often times I can even start it without touching the gas pedal. Its just the first start of the day that gives trouble. No, the choke is NOT connected. Maybe I'll mess with that and see if it helps.

BSB67

Does the accel pump function properly after it start?  If yes, the question is.....where does the gas go over night?    Consider raising the float level.

500" NA, Eddy head, pump gas, exhaust manifold with 2 1/2 exhaust with tailpipes
4150 lbs with driver, 3.23 gear, stock converter
11.68 @ 120.2 mph

moparnation74

Quote from: Kern Dog on March 30, 2017, 01:25:56 PM
No, the choke is NOT connected. Maybe I'll mess with that and see if it helps.
lol.....I would check that but I think I said that on FBBO....

Kern Dog

Quote from: moparnation74 on March 30, 2017, 05:04:54 PM
Quote from: Kern Dog on March 30, 2017, 01:25:56 PM
No, the choke is NOT connected. Maybe I'll mess with that and see if it helps.
lol.....I would check that but I think I said that on FBBO....


Hey, guess what??
Maybe I fixed it...(With some good suggestions)
I dug through my parts stash and found a choke spring and lever assembly that fits. It keeps the choke door closed when cold so that engine vacuum pulls fuel through. It starts without even pumping the pedal! I first tried holding the choke plate closed as I cranked the engine over. One pedal pump and it fired right up.
Thanks for the suggestions.

moparnation74

Quote from: Kern Dog on March 30, 2017, 07:08:58 PM
Quote from: moparnation74 on March 30, 2017, 05:04:54 PM
Quote from: Kern Dog on March 30, 2017, 01:25:56 PM
No, the choke is NOT connected. Maybe I'll mess with that and see if it helps.
lol.....I would check that but I think I said that on FBBO....


Hey, guess what??
Maybe I fixed it...(With some good suggestions)
I dug through my parts stash and found a choke spring and lever assembly that fits. It keeps the choke door closed when cold so that engine vacuum pulls fuel through. It starts without even pumping the pedal! I first tried holding the choke plate closed as I cranked the engine over. One pedal pump and it fired right up.
Thanks for the suggestions.
Awesome!  I thought the choke was the culprit...Especially, after you had an old schooler got through it :2thumbs:

c00nhunterjoe

If the accelerator pump doesnt squirt over night, how does 1 pump make it start? :scratchchin:

Dino

I had the exact same issue with mine. Ran like a champ but a pita to start if it sat too long. All it needed was a choke, who knew!   :lol:
Extraordinary claims require extraordinary evidence.

Kern Dog

Quote from: c00nhunterjoe on March 30, 2017, 07:18:32 PM
If the accelerator pump doesnt squirt over night, how does 1 pump make it start? :scratchchin:

I'm looking at this like I look at women.  It is fine now, I don't quite understand why or how but I'm just grateful that it is working.

Maybe these carburetors need the choke flap to be closed to induce the accelerator pump to work??? When the engine is running, engine vacuum aids in the accelerator pump function too I guess.

Every Thermoquad equipped vehicle I've owned  (Except ONE) was without a choke and every one of them was hard to start. I didn't drive any of them that often so I just thought the fuel had evaporated.

This is good news though. If I did actually stumble onto the reason why I have had trouble with these, I may use them in other cars. I have a 440 Power Wagon that could surely benefit from a bump in fuel economy!

c00nhunterjoe


flyinlow

Quote from: BSB67 on March 30, 2017, 04:45:34 PM
Does the accel pump function properly after it start?  If yes, the question is.....where does the gas go over night?    Consider raising the float level.



Yes, where is the gas in the Carb. going overnight?  The acc. pump will work  with a partial or slightly low fuel level. Proper choke operation is important with the plastic fantastic. It is not a Holley with super soaker sized acc. pump.

Try a different gas blend, without alcohol mix if possible. Fuel might be evaporating from a warm engine shut down. Fuel smell in the garage a couple hours after shutdown?