Thermoquad dry fuel bowl at cold start and restart

[Charlied]

Seems fuel bowls are dry on cold starts and restarts after a few hours.When cold have to crank for 8-10 seconds to fill, then it starts quickly. Holds steady idle (1000 rpm) and NOT running rich.
No evidence external leak. So would think an internal leak, but plugs are clean and given not running rich doesn’t support fuel leaking to intake.
Did a complete tear down and rebuild following Rocky’s road show about a year ago (excellent) and replaced gaskets in needle and seat location as well as those at the bottom of fuel bowl. I was meticulous.
Don’t think fuel can evaporate that fast.
Tested by starting cold and as soon as it was running shut it off (so fuel in bowl) left it overnight. Next morning pulled air cleaner manually pulled throttle 2-3 times watching the squirter, no squirt so bowls are empty, and since no real manifold heat with quick start and shut off think that eliminates evaporation. Stumped.


Any suggestions well appreciated. Thanks

 

[PurpleBeeper]

I'm no thermoquad expert.......but I can't think of any way a vacuum could be applied to suck the fuel out, and it won't evaporate that fast, so my GUESS is maybe a crack in the main body of the carburetor? It would have to be something that would let the fuel leak out

 

[pnora]

Did you re-glue the lower bowl wells. They are known for leaking.

 

[Cranky]

The lower bowl wells have 0-rings......are they still good?

 

[green440duster]

Lower bowl wells are the culprit 90% of the time. I had a great running carb on a Swinger with a 360 run great all day until you let it sit for more than 5 min then it would not start without a prime. New O- rings and fixed it right up.

 

[Cranky]

Once the lower bowls are right, then it's the secondary air door that needs to be addressed. That's where these carbs got their name ThermoBOGS....it's because no one knows how to set the the secondary air door. Not even the factory techs knew how to deal with them!! It's not that dang hard to do but it does take some experimenting to get it right. What works on the street might not work on the strip. Cars with good traction will show if it's right or not......

 

[Charlied]

Lower bowl wells are the culprit 90% of the time. I had a great running carb on a Swinger with a 360 run great all day until you let it sit for more than 5 min then it would not start without a prime. New O- rings and fixed it right up.

You have described exactly what is happening with me. Have new O-rings will install next week. I wonder if the ethanol gas has something to with it.
Funny thing is I have a 77 Vette ,all original, carb never touched and no problems.
Will let you know how it goes.
Thanks

 

[Charlied]

The lower bowl wells have 0-rings......are they still good?

Will replace them next week. How can I test before re-assembly of carb.

 

[Charlied]

Did you re-glue the lower bowl wells. They are known for leaking.

No, what’s a good adhesive to use ?
Thanks

 

[Charlied]

I'm no thermoquad expert.......but I can't think of any way a vacuum could be applied to suck the fuel out, and it won't evaporate that fast, so my GUESS is maybe a crack in the main body of the carburetor? It would have to be something that would let the fuel leak out

Will test bowl to be sure.
Thanks

 

[sam dupont]

I have glued the wells and the o rings in place with epoxy. The rings can hard to keep centered.
If you have a marble counter top (flat), it doesn't hurt to polish the body top with a sheet of 400 wet and dry to make sure it's square. Not too much, though.

Excuse my hijack, but... Out of frustration, I messed with this screw. Then I read in a manual that only the factory can set it. Not a shade tree skill level adjustment. Send it to a pro for a flow bench rebuild?

 

[MoparLeo]

When you have it apart pay close attention to the plastic accelerator pump hose. T-Quad has a hose from the pump to the nozzles which is unique to this carb. Often overlooked. A crack or poor fit can cause accelerator pump symptoms.

 

[4vnut]

This is the info I have had for years on how to set the "metering tree". Hope it is what you are looking for.

Metering rod tree adjustment,
with the fast idle cam not engaged, find the metering rod piston's center slot on the top of the piston center and with a small slot head screwdriver, lightly bottom the piston and turn the slot counter-clockwise until the piston stops dropping, then turn the slot clockwise noting exactly when the piston starts back up, still lightly bottoming the piston, turn the slot 1 turn clockwise. This is the correct way to dial-in the metering rod tree/piston. For a richer setting, turn the slot 1/4 more at a time. For a leaner setting, back off the slot counter-clockwise 1/4 turn.

 

[sam dupont]

This is the info I have had for years on how to set the "metering tree". Hope it is what you are looking for.

Metering rod tree adjustment,
with the fast idle cam not engaged, find the metering rod piston's center slot on the top of the piston center and with a small slot head screwdriver, lightly bottom the piston and turn the slot counter-clockwise until the piston stops dropping, then turn the slot clockwise noting exactly when the piston starts back up, still lightly bottoming the piston, turn the slot 1 turn clockwise. This is the correct way to dial-in the metering rod tree/piston. For a richer setting, turn the slot 1/4 more at a time. For a leaner setting, back off the slot counter-clockwise 1/4 turn.

Thank you. Who ever wrote the manual should have talked to you. I'm going to mess with that thing again. It must have some crap that I'm not getting. Another victim of setting.

 

[4vnut]

No, what’s a good adhesive to use ?
Thanks

Always had good luck with the JB Weld epoxy. Not the cures in 5 minute stuff. Surfaces must be clean for good adhesion as I'm sure you know.

 

[T2R9]

Thank you. Who ever wrote the manual should have talked to you. I'm going to mess with that thing again. It must have some crap that I'm not getting. Another victim of setting.

Also from your picture above the S link for the accelerator pump is on backwards. It should look like an S when looking at it from the front. It will affect your pump shot if backwards.

 

[T2R9]

I use Marine-Tex 2 part epoxy on the lower bowls when I rebuild TQ's. Not cheap compared to JB weld but it works well.

Amazon product ASIN B000Y8A06C

 

[sam dupont]

Also from your picture above the S link for the accelerator pump is on backwards. It should look like an S when looking at it from the front. It will affect your pump shot if backwards.

I stole that shot from the internet. I was studying the photo and it dawned on me, forehead slap, it isn't mine. whew.. but that's something to know.

 

[Charlied]

When you have it apart pay close attention to the plastic accelerator pump hose. T-Quad has a hose from the pump to the nozzles which is unique to this carb. Often overlooked. A crack or poor fit can cause accelerator pump symptoms.

Will do Thanks

 

[Charlied]

Always had good luck with the JB Weld epoxy. Not the cures in 5 minute stuff. Surfaces must be clean for good adhesion as I'm sure you know.

Thanks