Thermoquad help questions

[midnight340]

Hi All,

I have rebuilt the TQ and using a Mr. Gasket spacer to my LD340 for now. I did a bunch of work this morning to the spacer, gasket, and some on the intake opening to get nice smooth accurate alignment. Should help some.

But I have a couple of questions:

1) If I am not using a choke on my 340 for now, do I need the choke pull-off? I know they serve more than one purpose, but is that only if using a choke? (I have a new pull-off, but haven't found info as to whether I need it.)

2) My TQ is a '73 440 unit, and this model has what I assume to be a bowl vent pipe off the off the passenger side top plate. What do I do with this? Plug it? Route it somewhere?

Appreciate any help, thanks!

 

[RustyRatRod]

It must have the choke pulloff and it must be good. It also acts as the vacuum brake for the secondary air door so that it does not just drop open on acceleration.

 

[bbrroowwnn]

also LD340 is a squarebore manifold and the TQ is a spreadbore Carb

 

[bbrroowwnn]

you would have to hog it out like this

[FOR SALE] - LD340

 

[midnight340]

It must have the choke pulloff and it must be good. It also acts as the vacuum brake for the secondary air door so that it does not just drop open on acceleration.

Thanks Rusty, and I have a brand new one from Mike’s Carburetor.

also LD340 is a squarebore manifold and the TQ is a spreadbore Carb

Yes I know... mine is port-matched to my ported X heads, and I put hours into smoothing it out some, so it’s a keeper. The next time off I’ll modify it, until the it will run like this:

 

[midnight340]

I guess the pipe vent broke off but I have spare parts. So what do I need to do, replace this? then what?

Some of my parts carbs don’t have anything here.

 

[RustyRatRod]

I guess the pipe vent broke off but I have spare parts. So what do I need to do, replace this? then what?

Some of my parts carbs don’t have anything here.

View attachment 1715413673

I believe that just presses back in. I would clean it up good and put a small dab of sealer on it and just knock it back in with a small hammer.

 

[midnight340]

Then where does it go??

Also, I read in an old demonsizzler post that for performance you should drill out the accelerator nozzles to .031” (if I recall correctly, something close to that...)

 

[Dana]

The vent can and should be plugged, if the whole charcoal can setup isn't there. There is no one size fits all with squirters. Do not enlarge them if there isn't a problem getting out of the hole.

 

[318willrun]

Thanks Rusty, and I have a brand new one from Mike’s Carburetor.



Yes I know... mine is port-matched to my ported X heads, and I put hours into smoothing it out some, so it’s a keeper. The next time off I’ll modify it, until the it will run like this:
View attachment 1715413671

I think the secondary throttle plates might hit with just the 1" adaptor. Might want to check that. IF you floor it and they wedge it will pin the throttle open.

 

[rumblefish360]

Then where does it go??

Also, I read in an old demonsizzler post that for performance you should drill out the accelerator nozzles to .031” (if I recall correctly, something close to that...)

Do NOT drill out the squirter cluster until you know you need a bigger shot.

The vent can and should be plugged, if the whole charcoal can setup isn't there. There is no one size fits all with squirters. Do not enlarge them if there isn't a problem getting out of the hole.

The vent should remain open and not plugged up since it releases built up pressure that occurs from time to time within the fuel bowls. Fuel will not spill out. Reinstall it with a dab of lock tight for piles and tap it in if need be until it seats.

I think the secondary throttle plates might hit with just the 1" adaptor. Might want to check that. IF you floor it and they wedge it will pin the throttle open.

The secondary side should have absolutely ZERO issues contacting the intake manifold when the spaced is used.
Zero, none, Na-da, Zilch, etc

 

[midnight340]

I think the secondary throttle plates might hit with just the 1" adaptor. Might want to check that. IF you floor it and they wedge it will pin the throttle open.

I am running a stock type gasket and I reshaped the adapter quite a bit with a Dremel so am safe there.

Do NOT drill out the squirter cluster until you know you need a bigger shot.[/QUTE]

 

[midnight340]

OK , so I hear you say the tube once inserted just hangs out in the air as a vent. (But I do see my two 9000 series carbs aren’t even drilled in that location, seem to have a different small vent cast in.

 

[midnight340]

Gotcha. Easy to do later if need be. The reason I even considered it was because my motor liked a full shot through .043” nozzles on the Eddy 750.

 

[Dana]

Do NOT drill out the squirter cluster until you know you need a bigger shot.

The vent should remain open and not plugged up since it releases built up pressure that occurs from time to time within the fuel bowls. Fuel will not spill out. Reinstall it with a dab of lock tight for piles and tap it in if need be until it seats.

The secondary side should have absolutely ZERO issues contacting the intake manifold when the spaced is used.
Zero, none, Na-da, Zilch, etc

That TQ already has adequate venting. In fact we should all be using the electric bowl vent units with this pump gas that is 50% vapor @ 170*f. There are two was to vaporize a liquid: Add heat or reduce pressure.

 

[RustyRatRod]

The vent can and should be plugged, if the whole charcoal can setup isn't there. There is no one size fits all with squirters. Do not enlarge them if there isn't a problem getting out of the hole.

This^^^^^ you can plug the hole in the carburetor where the tube is already out, or, reinsert the tube like I described and slide a rubber plug over it. It's not the float bowl vent. It runs to the charcoal canister as described and if you don't have that, then that line is not needed.

 

[midnight340]

Excellent!! Thanks guys!!

 

[lemondana]

-midnight340- Your adapter that you show is for a Quadrajet. The Thermoquad adapter has more meat between the rear flange bolts. Hold that adapter up to the bottom of your TQ and you will see the potential for vacuum leaks on the TQ base.
Ask me how I know. Edelbrock has two different part numbers, one for a TQ and another for a QJet. Although they show the same picture for both.

 

[midnight340]

-midnight340- Your adapter that you show is for a Quadrajet. The Thermoquad adapter has more meat between the rear flange bolts. Hold that adapter up to the bottom of your TQ and you will see the potential for vacuum leaks on the TQ base.
Ask me how I know. Edelbrock has two different part numbers, one for a TQ and another for a QJet. Although they show the same picture for both.

I will check this out. I am sure I was swayed by the price, when they appeared to be the same. The Edelbrock #2691 ($46.00)probably would not have required the reshaping I did with the dremel on the Mr. Gasket #1932 ($21.00.). But I will take a close look tomorrow.

 

[rumblefish360]

Gotcha. Easy to do later if need be. The reason I even considered it was because my motor liked a full shot through .043” nozzles on the Eddy 750.

The 750 Edelbrock has a larger primary bore than the small TQ. On the larger TQ, I’d have to run calipers to find out the diameter of the venturi’s narrowest point. That’s half the equation. The double booster ring up top is the other.

 

[midnight340]

-midnight340- Your adapter that you show is for a Quadrajet. The Thermoquad adapter has more meat between the rear flange bolts. Hold that adapter up to the bottom of your TQ and you will see the potential for vacuum leaks on the TQ base.
Ask me how I know. Edelbrock has two different part numbers, one for a TQ and another for a QJet. Although they show the same picture for both.

I see what you mean when putting the adapter against the carb, but using the thick gasket looks like it will solve that. It covers the entire base of the carb.

The 750 Edelbrock has a larger primary bore than the small TQ. On the larger TQ, I’d have to run calipers to find out the diameter of the venturi’s narrowest point. That’s half the equation. The double booster ring up top is the other.

Ah,I see! That makes total sense once you explain the differences in the primaries. Thanks!

 

[rumblefish360]

No worries. The double booster keeps incoming air at a higher speed to help atomized the fuel. It’s main purpose is for the fuel out of the discharge nozzle but the extra area will also effect the discharge out of the pumpshot.

Make sure you reset the pump arms height after moving the position of the rod.

 

[midnight340]

OK, up and running. All settings were done according the manuals as I rebuilt it.

Improved throttle response over the 750 Edelbrock, even though I'm not getting a vacuum signal from the port on front. 6518S carb (440 Industrial) with only one port for distributor on front and the port for the pull-off in back.

If I blip the throttle lever I get vacuum for a split second, then back to zero. So driving I probably get some advance for just a bit.

I can adjust idle mix to 14-15 on the A/F meter, but with any throttle at all, it goes to the meter limit of 10 A/F. Running along at low speed cruise (idle circuit) it's OK, but then with throttle in the 10's at best. I backed off the small screw on the rods and it seemed to help just a bit. But I'm way rich.

Does seem to have some unevenness mid throttle. So where do I start??

 

[rumblefish360]

With identifying the rods you have and there dimensions.
You came up with a number that can not be cross referenced with the Vannth guide, so you need to measure the tip and the next one or two steps of the rod.
Let us know the sizes.

The rods hang on the “tree” which has a central, in the middle, piston that rises and falls with vacuum. If your not generating enough vacuum, the tree rises early and enrichens the carb to early giving you that dead stupid rich condition. There is a spring under the tree’s piston. It is larger than an AVS or AFB spring. Delete the spring. In the base plate is a cam that will raise a level for a manual enriching of the carb.

The tree’s center where the adjusting screw is raises and lowers the rods in the jet. To lean out the mixture some at idle , spin the screw to drop the tree downwards. This also delays enrichment.

You won’t get a vacuum signal from the port up front because it is a timed port for the distributor. This is normal and how Chrysler set up the system. It doesn’t see vacuum until you open up the throttle a little. Try from the rear port instead.

You never gave any description to the engine. Compression ratio, cam, headers????

 

[midnight340]

Engine and cam notes:
9:1 compression 340, ported X heads, 1-5/8" headers, MSD ignition, headers and LD340 intake port matched.
...cam is a Lunati solid.(Advertised Duration (Int/Exh): 264/272 ;Duration @ .050 (Int/Exh): 235/243 ;Gross Valve Lift (Int/Exh): .525/.546 ;LSA/ICL: 110/106 ;Valve Lash (Int/Exh): .016/.016 ;RPM Range: 2400-6600)

The rods measure at 67/57/45. They have a 45 section but the 57-67 is a taper. And the jets (can't remember at the moment) are the same as what were used in the stock '73 800 340 carbs, so should be close.

I hear you say I should remove the spring for the rods tree?? And it will work with just the mechanical cam lift.
Since I'm used to the Edelbrock drivers side being manifold vacuum, I never thought about it being timed/ported. So to set idle mix by vacuum I can use the rear port (used for the pull-off.)

Thanks, rumblefish360, this will get me on the right track. Even with the overly rich condition I was really liking the throttle response. Looking forward to getting this thing dialed in!!