• When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

Thermoquads fuel vapor connector

Jc cooper

Jc cooper

Second gear fun!
FBBO Gold Member
Local time
9:09 AM
Joined
Jan 2, 2017
Messages
700
Reaction score
403
Location
Houston tx
Thermoquads fuel vapor connector, does it need to be capped on 440 , carb is 6322s or leave open , not original carb for this 67 gtx
 
Agreed , cap it. At 170* F Our pump gas is about 50% vapor. So, the less atmosphere you expose the fuel to, the less it will evaporate.
 
Be aware that this is the external bowl vent your talking about I believe that would go to a charcoal canister normally. Uncapped when hot the gas fumes will go into the air. But when capped the fuel vapors can now only vent by the internal bowl vent which will vent into the carb throat and into the eng. So on a hot day this cheap pump gas can start to boil in the carb bowl if it gets to hot and then it will push all the fuel vapors into the eng and flood the eng out. I have had it happen with Holley carbs but the plastic bowl should help on the thermoquad. So just be aware that if you leave that capped you may have some hot soak problems of the eng being flooded real easy. Like if you take a 30 minute drive on a hot day and then stop for 10 minutes and go back to start the car and if you hit the gas while starting you may flood the eng out since all fuel vapors are going into the eng. That external bowl vent is normally made to open at idle and close when on the gas until they started putting all the emissions things on cars and then the one on the thermoquad used a solenoid and vacuum to control when it was open and closed which yours could have as they used a few different ones on them. So just be aware if you cap it and have hot soak starting problems. Myself I would put a hose on it and run it down on the side of the eng and leave it open. It will let vapors into the air on hot days but will help against heat soak. I dont think leaving it open will hinder performance as carbs are designed to have the external bowl vent closed when driving down the road and use the internal bowl vent when driving along as thats a balanced carb but I dont think leaving that open all the time will make enough difference to be felt and having it open at idle on a hot eng will be a big help. Ron
 
Agreed, for a street driven application, capping off the idle fuel bowl valve vent nipple can only contribute to potential hot start issues, defeats the purpose of the idle fuel bowl vent valve. If not running an evaporative recovery system, the nipple should be left open to the atmosphere.
 
Primary bowl vent tubes? Are not hose nipples. There is only one enclosed idle bowl vent valve hose nipple, external to the air filter element. The intended purpose of the enclosed idle vent valve hose nipple has nothing to do with the primary internal bowl vents.
 
Last edited:
Perhaps you should look a little closer at that upper casting the next time you have one open. The external vent valve nipple is the only passage that leads to a valve that closes off that passage when the throttle position is off-idle. You can not equate this vent valve nipple with the primary bowl vents in any way. Again, the intended purpose of the enclosed idle vent valve and related hose nipple has nothing to do with the primary internal bowl vents.

A bit surprised a business that appears to be specializing in rebuilding/restoring carburetors seems not to understand the function of idle bowl vent valves. Their use pre-dates evaporative recovery systems.
 
DFC99416-2520-4BA6-97D6-470C37CF46E9.jpeg
This is a 2124 air horn the top part of all production 6322 Thermoquds. The yellow dot is where the external bowl vent exits. The green arrows are the 3 bowl vents that exit into the air cleaner. The red lines are their path of travel. If the your theory of the 6322 external bowl vent were right, then every single aftermarket Holley would have hot start issues, especially since they are of all metal construction. If you apply your theory to the electronic bowl vent TQ’s them you’ve got something. The OP has a 67 GTX and I presume no charcoal canister, so then he cannot connect the purge port in the baseplate to even make it a closed loop, as was intended. So that don’t hold water either. I don’t appreciate you insulting me and my lively hood. Guys like you are the reason I am reluctant to help out on these forums.
 
Not my intention to insult anyone, merely expressing an observation. Your picture shows the idle bowl vent valve removed, does it not? My theory? No, idle bowl vent valves are quite common on OE carbs from this time period, both open and later enclosed, including all the OE Holleys. This discussion is not about aftermarket carbs, as stated, few aftermarket carbs today include them. Many replacement aftermarket carbs from the day had them, however.
Purge port? Closed loop? On a vehicle not running a evaporative recovery system using a charcoal canister, the purge port would not be used, nothing to be purged, the purge port would need to be capped off. The purge port has nothing to do with the primary function of the idle fuel bowl vent valve.




bowl vent valve.JPG
 
Last edited:
Thanks guys for the discussion on the vent situation on 6322 carter thermo , open conversation so often brings about educated lines of reasoning , not challenges of ones skill or intelligence on any given subject, in my life, I have gained much knowledge, by chewing the cud , thank you and may Peace and Harmony prevail ! Traveler !
 
It only has the one external bowl vent and the internal vents that vent the bowl to the air horn. Depending on the year as to how the external bowl vent works as some are just mechanical and have the arm that open the external vent at idle and closes it off idle. Others use a solenoid and vacuum to open or close the external bowl vent as on that one it uses vacuum to close the external bowl vent when started and then has the electric solenoid to keep the vent closed when running so if you step on the gas and the vacuum drops the solenoid still holds it closed when running. When its running and the external bowl vent is closed it then opens the bowl to the internal bowl vents so its a balanced carb and vents the bowls to the airhorn which can change from normal atmospheric pressure when running with the air going down into the eng by the internal bowl vents. It only has one nipple that is for the external bowl vents that vent the bowls to external atmospheric pressure. Some will have about 3 vents that vent internally to the air horn and none of them are the external bowl vent. Like I said the external bowl vent was worked a few different ways over the years that carb was used due to the emissions laws. Ron
 
Latest update on the 6322 Thermoquad carb , after the lively conversation about the bowl vent on this carb as to close it off or leave it open , I decided to close as a working experiment, now even after a week of not driving, it starts right up and has no fuel issues and no vapor lock whatsoever! Thanks Guys
 
To be clear, original the purpose of the idle bowl vent valve has nothing to do with vapor lock or cold start. Good luck.
 
As said the only time it will give problems with heat soak and flooding on starts is on a hot start in hot weather. Even on a hot day when first started it will start fine because the eng is cold but drive the car 15 miles on a hot 90 degree day and then park the car for 15 minutes and then when you go to start it all the fuel vapors that can be from the hot eng sitting a few minutes will only go into the eng and if you hit the gas pedal as starting that hot eng it may flood and be hard to start. Thats why that bowl vent is made to be open at normal idle with the eng off. It wont make a starting problem starting a cold eng because there has been no heat in the eng to cause any fuel vapors in the carb to rise up and go somewhere which will be into the eng out of the carbs internal bowl vent. So you should not have a problem on a cold eng even on a hot day as long as the car has been sitting in shade and the eng is cold you should have no problem. Its a hot soak as its called when you will have a rich condition. Ron
 
383man said:
As said the only time it will give problems with heat soak and flooding on starts is on a hot start in hot weather. Even on a hot day when first started it will start fine because the eng is cold but drive the car 15 miles on a hot 90 degree day and then park the car for 15 minutes and then when you go to start it all the fuel vapors that can be from the hot eng sitting a few minutes will only go into the eng and if you hit the gas pedal as starting that hot eng it may flood and be hard to start. Thats why that bowl vent is made to be open at normal idle with the eng off. It wont make a starting problem starting a cold eng because there has been no heat in the eng to cause any fuel vapors in the carb to rise up and go somewhere which will be into the eng out of the carbs internal bowl vent. So you should not have a problem on a cold eng even on a hot day as long as the car has been sitting in shade and the eng is cold you should have no problem. Its a hot soak as its called when you will have a rich condition. Ron
Click to expand...
Ok will keep eye out for problems, if any easy enough to remove rubber cap from it , not big deal either way!!!!!
 
You must log in or register to reply here.

Similar threads

70b5bluerunner
69 Coronet R/T fuel pump
Replies
12
Views
469
turbine68rt
turbine68rt
Rob'68Net
Vapor Return lines
Replies
10
Views
538
68 Sport Satellite
68 Sport Satellite
P
fuel line
Replies
0
Views
293
paul1969cars
P
Vanderstel
Fuel drips when gassing up
Replies
4
Views
654
kiwigtx
kiwigtx
7
71 GTX Vapor return line/tube
Replies
3
Views
763
Bee1971
Bee1971
Auto Transport Service
Back
Top