Carter Thermoquad carb stalls at idle in gears & doesn´t start & let the fuel in carb

[moparmarkus]

I changed to a late seventies Carter Thermoquad (see pic), an autolite reman last year. Specs: 1968 Charger, 1974 440, mech. fuel pump, ecu ignition, stock 727, 3.23 open gears.

Car cold starts fine, accelerates strong, I´m quite happy with this carb, except one thing:

When engine is warm/hot and idles in gears (at a stop sign) oil pressure drops, temp rises and it nearly stalls. I have no Air Fuel gauge, sorry. But there is one hint: A warm/ hot start is impossible, because there is no fuel in carb, there is high pressure in the fuel line at carb inlet. But it seems the carb doesn´t let the fuel in. If I throw a bit of fuel direct into the two front barrels - it starts and runs with idle in neutral or drives in gears.

The TQ is an autolite reman, I had it disassembled over the winter, it was very clean and everything looked unworn or new in my opinion. It seems to be closed or clogged by high pressure or a vacuum. What do you think? Has anybody had a simmilar fault on his TQ?

 

[Coronet 14]

Could be the fuel you are using. Try higher Octane or Non Ethonol fuel. If it starts and runs when cold I think your fuel delivery is ok. Is Choke opening all the way Just a suggestion

 

[WileERobby]

Most Late 70's TQ's are lean-burn carbs... better to use the early non-LB carbs.

 

[mopar 3 B]

Where are you getting distributor vacuum from? Have all smog devices been removed from the carb? What about fuel bowl venting. Many of the later TQ where vented threw the charcoal cannister if you have pluged the vent lines on the TQ it may not be allowing proper fuel delivery. Did you follow all steps and in proper order upon assembly after taking the carb apart?

 

[moparmarkus]

Could be the fuel you are using. Try higher Octane or Non Ethonol fuel. If it starts and runs when cold I think your fuel delivery is ok. Is Choke opening all the way Just a suggestion

Choke works fine untill it´s fully opened. When the carb gets warm/ hot it hardly let the fuel into it until it´s get´s fully closed by something.

Most Late 70's TQ's are lean-burn carbs... better to use the early non-LB carbs.

...yea, I should have changed the manifold to a squarebore instead of changing to a spreadbore TQ, but I really like the smooth acceleration of the TQ. Lean is ok, but it doesn´t let the fuel in until it stalls.

Where are you getting distributor vacuum from? Have all smog devices been removed from the carb? What about fuel bowl venting. Many of the later TQ where vented threw the charcoal cannister if you have pluged the vent lines on the TQ it may not be allowing proper fuel delivery. Did you follow all steps and in proper order upon assembly after taking the carb apart?

I get the distributor vacuum from the front of the carb (driver side), pcv valve also front (middle) and brake booster from manifold. All other ports are unused and plugged. The stall problem appeared also before Dis- and assembly was done by specs in the carter manual. Everything include bowl are super clean, float needles and seats are new.

Fuel bowl venting? You mean if there is no ventilation, there could build up excess pressure in the bowls and wouldn´t allow float needles to open to let the fuel in... good idea! Sounds logic!:idea1:

...idle in neutral or driving in gears releases the pressure and idle in gears build up pressure, but how to solve...hm:shruggy:

 

[rumblefish360]

The charcoal canister bowl vent should be left uncapped.
The float drop should be rechecked. Extra fuel in the bowl is better. It will also slightly enriched the carb.
Fuel pressure could be dropping when hot.
I can not see the picture so well on the phone, but, are you running the thick OE type gasket. Since the TQ is a phenolic resign sandwiched between to aluminum parts, heat, or to much in this case can cause fuel to boil right in the bowl.
Recheck tune so your not lean.

 

[67 coronet]

your bowel vent appears to be capped.its the tube sticking out on top passenger side of carb.hook a cheep fuel filter to the end of a short line and hook to it.(fuel filter is so nothing gets into carb through the line.)that should test that idea.biggest prob I have had with those carbs is fuel leaking internally from warpage between phenolic section and aluminium sections of carb.

 

[WileERobby]

your bowel vent appears to be capped.

If that's the case, he 's got more serious problems than the car...

 

[mopar 3 B]

Uncap the bowl vent. No need to filter it. Check the port you are using for distributor vacuum ( disconnect the hose and spray some pressurized lubricant into the port) should come out above the butterfly. If it does it is ok if not you are using manifold vaccuum instead of carb port vaccuum and will cause the distributor to run full vacuum advance. This will not be noticed until the choke releases explaining why it runs ok cold. The TQ is a temperamental critter to adjust everything must be done in the proper order or settings will not be correct.
Which spacer or adaptor are you using - the open 1 hole or the offset 4 hole?

 

[moparmarkus]

If that's the case, he 's got more serious problems than the car...

Just my backbone is acing a bit, everything else is fine, thank you. :icon_mrgreen: The pic was taken after first installation and the silver tape was removed prior starting first time, so the big port on the pass side is free.

 

[moparmarkus]

Uncap the bowl vent. No need to filter it. Check the port you are using for distributor vacuum ( disconnect the hose and spray some pressurized lubricant into the port) should come out above the butterfly. If it does it is ok if not you are using manifold vaccuum instead of carb port vaccuum and will cause the distributor to run full vacuum advance. This will not be noticed until the choke releases explaining why it runs ok cold. The TQ is a temperamental critter to adjust everything must be done in the proper order or settings will not be correct.
Which spacer or adaptor are you using - the open 1 hole or the offset 4 hole?

I use the OE gasket on a 74´ spreadbore manifold as shown above. I connected distributor vacuum as shown in the carter manual, but will check again.

Thanks a lot for your help so far. I´m really happy to found some TQ experts! :sSig_thankyou:

1st Block the internal bowl vent "door" in an slightly open position to allow constant "breathing" of the bowl.
2nd Check the distributor vacuum port.
3rd Recheck float level.

 

[idrivemopar]

I would replace the blue cap that is on the purge inlet with one that is thick rubber, those cheap plastic ones get really pliable and loose when hot, could be causing a vacuum leak there, and make sure the actual inlet is not loose, I have seen a few come loose and cause vacuum issues. Also check for leaks around the butterfly rods on the bottom plate, you can spray some brake clean or something like that at the base where the rods come out and if you hear the rpms go up, they are leaking, however, assuming since it was remanufactured, they should have bushed the rods if it were a problem.

 

[WileERobby]

A word of caution. Just because it's a reman part, doesn't mean it's good. Just did a job for a friend, chasing our tail only to find out the NEW replacement part I thought was the culprit ( which it was) turned out to be defective.

 

[mopar 3 B]

I have been threw this thread more than a few times and just makes no sense. I have had more problems with TQ's dumping to much fuel and never from not enough. Just the fact that it runs fine until hot would point to a fuel dilevery problem. So there is pressure in the line at the carb when hot but is there fuel? Ditch the rubber fuel line from the pump to the carb. It will hold heat longer than metal. Route the fuel line to the front of the engine and over the top of the intake manifold. Keep the fuel line as far as possible from the engine block and intake manifold. Never run fuel lines over exhuast manifolds or headers and nevér lay them on cast iron.

 

[Irv Turner]

sounds like you have a fuel delivery problem. see if the inlet line is hot it could be vapor locking. try to put a few wooden clothes pins on the steel part of the fuel line close to the carb. some times the fuel line is to close to a heat source. also there are two small O-rings in the bottom of the carb at the fuel wells makes sure they are there the white sealer at the bottom of the black plastic fuel well can leak. I love those carbs.

 

[mopar 3 B]

sounds like you have a fuel delivery problem. see if the inlet line is hot it could be vapor locking. try to put a few wooden clothes pins on the steel part of the fuel line close to the carb. some times the fuel line is to close to a heat source. also there are two small O-rings in the bottom of the carb at the fuel wells makes sure they are there the white sealer at the bottom of the black plastic fuel well can leak. I love those carbs.

It's got rubber hose going to the carb. Clothes pins will be worthless. If the fuel wells were leaking it would not run well cold eather.

 

[moparmarkus]

Problem is solved now! Thank you guys a lot for your kind help! Car runs strong again, especially with idle in gears! :headbang:

In fact the bowl vent linkage was (incorrectly) bend and kept the bowl vent flap inside the bowl closed in idle. In my theory the rising heat builds up more and more pressure inside the bowls until I have to stop in traffic, then the float needles got stuck in their seats and blocked the fuel delivery until engine stalls.

I had this situation once again at a red light in front of a huge crossing... embarrasing... lifted hood an aircleaner, disconected fuel hose and held it right into the carb to let some fuel drip into - reassembled and turned the key while holding the gas and car ran as when nothing happened... until the next red light, but I went another way back home and immediately bend the linkage the right way so the bowl vent is always in open position in idle and closed between quarter and half throttle. I will post a picture with markings of the linkage the next days.

 

[383man]

The external bowl vent should be open at idle so it will have atmospheric pressure on the fuel in the bowl at idle. It should close just after idle so that the internal bowl vent is venting the fuel in the bowl to air horn pressure when on the gas driving along. That makes it a balanced carb. If the external bowl vent was open when driving down the road it would still have atmospheric pressure on the fuel in the bowl driving along and it should be air horn pressure when driving as the carb is calibrated that way and if the external bowl vent stays open going down the road with your foot on the gas it can run to rich since that carb is calibrated for air horn pressure on the fuel in the bowl with the throttle off idle. Ford actually had a TSB about that in the late 70's for their Autolite 4 barell carb running to rich going down the road if the external vent was open off idle. Ron

 

[moparmarkus]

if the external bowl vent stays open going down the road with your foot on the gas it can run to rich

Ah, that may be the reason why acceleration felt a little less then before, after the tune up yesterday. I will correct that to a just slightly open bowl vent in idle and closed position on gas. Thanks again!

 

[idrivemopar]

Great info. Thanks 383man for the explanation, nice to learn something new!