How to tune ThermoQuad secondaries?

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Air door spring needs to be tighter. I found that the recommended amount of turns was never enough. I ended up with 2 1/2 to 3.Just keep tightening it until the stumble goes away.Punch it,get out and adjust,repeat...
 
Have you done anything with the step up spring or rod hanger in the primaries? If it was lean there (not way lean, but lean) it will make the secondary lean much worse feeling. By adjusting the screw on the hanger you can time when the primary power enrichment comes in, or remove it almost entirely... And yes, it if was me, I'd put more tension on that air door. You have a small engine that is not breathing well (single pipe) and the secondaries I think are too much for it. So add more preload (like -56 turns past closed) and try that.
 
Well, I've been trying to tune the primaries by the spark plugs, but I have to drive it around without the secondaries for a while so that I get an accurate reading. I really wish I didn't still have single exhaust, I'm sure I'm giving up a lot of power (and gas mileage) right there.
 
Kid - why don't we aim for a benchmark so we know where its at - and then go from there.

ATM its hard to provide advice because we don't know your primary jetting, rod size, rod setting or air door tension....

Try to answer the questions at the end of this post so we have more data.

So -

1/ Set your air door spring at turns past "closed". (If you tighten the spring too much it can break).

2/ - Set your tree at 3 turns off base point. (see questions below)

3/ - Bend your air door stop tab upwards (when the door is horizontal) a lttle bit - this richens the A/F at WOT. See pic.

P1010016.jpg


NOW -

Please get back to us with this info-

1/ What size primary jet are you running?
2/ What is the rod # you are running?
3/ Did you check how far the secondary valves are opening? See pic.


P1010017.jpg


See how the secondary valves are not guite vertical - this is correct. IF yours are opening too wide (completley vertical) , you'll have a massive lean out at WOT.


After you do the chages and give us the info, we can help you more.
 
After driving around with just the primaries and then checking the plugs they show that I'm actually running rich, so I think the primaries are fine (although I did lean the tree out about a 1/2 turn).

Primary jets are #98, and metering rods are #2377. BTW I have the tab on the air door already bent up a little bit.
 
I just watched that vid - and I agree its a lean out.

Check your spray bars for blockages, bend the tab a little more, and run the door on 4 full turns.

Before you drive it - remove the air cleaner and double check to make sure the door is pulling open cleanly.

I am going to check your rod/jet combo against my data - and Ill post back.
 
I just went out and did a couple trial runs, starting at 3 turns and going up in 1/2 turn increments and it still bogged no matter what. I got it all the way to 6 turns and it still falls on its face.

EDIT: I know the spray bars are flowing fuel because after every run the engine smells of gas and the air door is wet (on both sides). I almost want to use a video camera to record the carburetor as I floor it so I can see exactly what's going on. OH and it bogs no matter how far I open the secondary butterflies.
 
OK, I checked the TQ Vaanth guide - the 2377 rod is not listed, but on the scale of numbering it looks like it is a very lean rod.

Do you have measuring calipers (vernier) that you cam measure the rich stage of the rod?

Maybe Demon Sizzler will chime in on his opinion of your primary rods/jets - but I reckon they are far too lean.

Anyhow I have revised my suggestion for a benck mark -

Aim for the richest setting you can get it on (about 4 turns on the tree, bend the air door tab some more, and set the air door spring to around 4 turns-
 
OK gotcha -

Guess we need to make sure the door tension changes as you tighten and loosen it?

What spares do you have, extra primary or sec jets? Any other rods?

Im trying to get your carb to be configured a slightly leaner version of mine (I run a small stroker 318 with a slighlty bigger cam) - but I need ot know what parts you have?
 
I don't have any other tuning parts for this carburetor. I also don't have those calipers you mentioned...

After I'd tighten the air door I'd push down on the door to check the tension and at 6 turns it was pretty damn tight.
 
OK, I think we're going in the wrong direction here. I bent the tang a little more and adjusted the metering rod tree to 4 turns like you said (the air door was still at 6 turns), and when I took it out it bogged just like (if not worse than) before. Also as soon as I pulled in the garage I pulled one of the plugs and it was almost entirely black.
 
Problem - The real issue here is that the car never recovers from the "bog" once the secs tip in - and thats got to be a "mixture" issue.

Air DOor - Its bogging at whatever tension you set it at - so its not the door tension alone thats causing the problem. In reality its probably too tight at 6 turns - the door usually only needs a small amount of resistance - but thats not really the issue as you've discovered. Set it back to around 3 turns.

Conclusion - My own gut feeling is that the carb is still too lean and your primaries are not helping the situation.

Your primary rods are very lean, and your .098 primary jets are on the leaner side of "Best case"

I know you think its set rich on the primaries - but with those rods and jets I seriously doubt it.

Here's what Id do:

- Remove the primary/sec linkage to isolate the primaries.
- Tie off the sec butterfly valves in the closed position with a cable tie.
- Set the tree on the absolute richest setting you can (Be careful not to raise it too far - or it will foul on the small retainer plate as the throttle shaft pushes it upwards...about 4 turns of base is the max you can go.

Take it out and see if it blows blue smoke when you nail it. If it doesn't, you still have room to move to a richer jet on the primary side.

Once you know its not too rich on the primaries,- you have two choices -

1 / Drill the primaries to .101 and see what happens , or

2/ Buy some .101 primary jets, some 1966 rods and a spare set of secondaries from Demon and ask him to recommend a baseline tune.

Either way - leave the air door at a "medium setting - as we know its not the whole issue - and decide if you want to really test the jetting.

After all, you did say the change to .140 secs improved it slightly, yes?
 
I hardly noticed a difference with the drilled-out secondary jets. Also, when I drove around with just the primaries after I adjusted the tree to 4 turns it ran completely normal. I don't know if any smoke came out though because it's 10 o' clock here and I couldn't see. BTW wouldn't it be black smoke if it was too rich?

I'm going to call it a day at this point and (maybe) continue tomorrow, I'm not too psyched about wasting all this gas.
 
Not sure on colour - depends how rich it goes I think - but if you set the tree at four turns and there's no smoke - its clearly got room to move.

Drilling the primaries won't upset the apple cart too much,

FWIW - I set mine at:

  • .101 primaries,
  • Three turns on the tree
  • 75-1996 rods : .069 .048 .035
  • .141 secondaries
  • 2 turns on the air door, door tab bent upwards.

I know your combo is a little milder - but you only have to be little way lean and they'll behave like a pig.

Proof? - With a .125 secondary in mine, and everything else the same - it absolutely "flat lined" like yours is.
 
Damn, that sucks. I suppose I'll cruise around on the primaries until I can get those replacement parts. This has been very frustrating, but thanks a bunch for your help anyway. Some day my Duster will grow some balls and stop being a pig...
 
Moparmal said:
Not sure on colour - depends how rich it goes I think - but if you set the tree at four turns and there's no smoke - its clearly got room to move.

Drilling the primaries won't upset the apple cart too much,

FWIW - I set mine at:
  • .101 primaries,
  • Three turns on the tree
  • 75-1996 rods : .069 .048 .035
  • .141 secondaries
  • 2 turns on the air door, door tab bent upwards.
I know your combo is a little milder - but you only have to be little way lean and they'll behave like a pig.

Proof? - With a .125 secondary in mine, and everything else the same - it absolutely "flat lined" like yours is.
Click to expand...

Just a quick question, what's the altitude where you're located?
 
209 ft above sea level - temp is around 60 deg F with low humidity (its winter down here)

Today i set a new PB 0-60mph using a G-Tech with a TQ jetted exactly as above - 4.90 secs. And I had to crawl out of the hole to avoid crazy wheel spin.
 
Moparmal said:
209 ft above sea level - temp is around 60 deg F with low humidity (its winter down here)

Today i set a new PB 0-60mph using a G-Tech with a TQ jetted exactly as above - 4.90 secs. And I had to crawl out of the hole to avoid crazy wheel spin.
Click to expand...

Well that kind of changes things... Remember, I'm at around 7000 ft. above sea level in the Rocky Mountains.
 
Fair and reasonable point on the altitude, but the engine is clearly starving so we have to work out why.

Sometimes its possible to go straight past the point where you need to be - by concentrating on the wrong target..

so I suspect running the air door so tight may have created another problem not related to the original issue.


First - Before closing the hood and driving it - Get someone to give it a blast on the throttle while you watch the air door (DONT put your face too close to the carb!) - or move the throttle linkage yourself

Check and make sure the secondary valves and the air door are opening properly, it shouldn't flop open, but it should open also shouldn't "resist" opening as well. At 2.5 turns after the door goes level it should be about the right tension.

Your metering rods worry me - they are about as lean as you can get for a TQ, so your primary setting will be dragging your WOT fuel settings right down.

I reckon its "roll the dice" time for you - so before you give up, Id take a chance and richen the primaries significantly - drill them to .103 , three turns on the tree and set the air door at 2.5 turns.

Use the .140 secondaries

The idea is to make it "fatter" than it should be - but not insane - to see if the car starts to run properly - at least it will show it was too lean before.

- and then take it out and see if it drives behaves any better.

Also, what type of air cleaner are you running? TQs are very sensitive to disturbed air flow. Some aftermarket air boxes, and some smaller filters, really muck them up.
 
MOPEkidD-3 said:
Well that kind of changes things... Remember, I'm at around 7000 ft. above sea level in the Rocky Mountains.
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I know it is an old thread, and you have probably ditched the TQ by now, but I was reading this and wondered, have to checked the Choke Vacuum Pot? I had one go bad, only 3 months old, and it would not pull down. It exibited the exact problem you are mentioning. I tried that secondary door spring every which way, and bent that tab repeatedly. I accidently stumbled across the Dash Pot being bad! Hook a vacuum source to it, and see if it pulls down. Mine would pull down, but I could easily pull it back out, while the vacuum was still engaged. You should not be able to pull it open easily.

Also, when the dash pot is pulled down, there should be very little play in the secondary door, mine has none!

Let me know if this helps.

Jimmyray
 
A big problem with the thermoquad is the main body warps and leaks (vacuum and gas). Only way to fix that is to machine it flat again. But I still prefer a Carter over a Holley. If you are going to drill out jets remember that you can't hold it in your hand when drilling. You need to have it rigidly mounted on a drill press to make a nice round hole.
Lynn
 
Thanks for the tip but I took that carb off months ago, it just turned out to be way off in pretty much every aspect... My MPG went up by 3 just swapping to a known-working AFB even when I was taking advantage of the working secondaries :evil4:

If/when I do try another ThermoQuad I'm going to get a core that's set up as close as possible to my engine combo from the factory and have it tuned by DemonSizzler from there if it doesn't run well. I just gotta see it professionally done before I can figure it out myself. I think my cousin is actually wanting to get one for his 440 Polara to improve gas mileage so we'll see.
 
MopaR&D said:
I think it's time to give up on this carb. I epoxy'd those two holes in the front of the primary air horn and although it idles a bit better now, it still does the same exact thing when I open the secondaries. I took it out for the umpteenth time to try to tune the air-door tension and again, no matter how tight or loose the spring is set it bogs (just like before) as soon as I tip into the secondaries, then pulls hard for a split second when I let off (followed by a faint puff of black smoke out the tailpipe that I can see in my mirror).
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check the acceleration pump CUP, ethanol can eat them, result is as you stated, had similar issue, and it was the pump CUP .
also the fuel bowl, when inverted has 2 well caps they might be leaking. this would cause the leakage and engine flooding/rich .
I say this due to my current experience with my TQ's
 
slant6/4speed said:
A big problem with the thermoquad is the main body warps and leaks (vacuum and gas). Only way to fix that is to machine it flat again. But I still prefer a Carter over a Holley. If you are going to drill out jets remember that you can't hold it in your hand when drilling. You need to have it rigidly mounted on a drill press to make a nice round hole.
Lynn
Click to expand...
I never had a fuel bowl warp, did experience fuel bowl caps leaking. Also careful with using electric fuel pump, pressure may be to high causing leakage at the cover gasket
 
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