My first Thermoquad tuning question!

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Locomotion

Locomotion

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Took my NHRA Aspen wagon out Saturday with a test engine to make sure all the suspension mods worked and it went straight. Car ran well for what it is (7.57-7.61 @ around 88mph in the 1/8 w/1.57-1.58 60'.) But on the burnout, I started in first and before I got it wound up in 2nd, it fell on its face and stayed around 3k - 3.5k even with my foot on the floor. The subsequent run was fine. Would like to know what to work on next time out.

* Would the secondary adjustment be too light?

* What are the smallest tuning increments that would show a performance difference in a run? (1/8 turn, 1/4 turn, etc.)
 
I would think spring is to light. Go 1/4 turn until you go to far (slower 60) 1/8 back to dial in.
I've only really fine tuned a TQ for street performance with a wideband.
I adjust spring rate for smooth secondary transition in 2nd gear pulls.
WOT AFR is dialed in with jetting and really fine tuned with air door opening stop.
 
hi, how many wraps on air door spring? also, the choke linkage has to be blocked open.
on throttle side of carb. you don't want it to move at all. I think your air door is too tight. on our 340, its set vertical, then tighten spring until it just closes. mine would blubber in water box, before. a s/s racer said door was too tight. it was opening and closing. so , loosened it up, problem went away. also, did you drill out back of vacuum canister? we done that, it let 's door open faster, without delay. BTW , this is a 340 stocker. not a street car!!!
 
when the secondaries do not open, it has no power, and will not rev up!!! if it was rich it would pop and miss. we've been using a TQ on 340 stock eliminator for long time. we had to overcome problems.
 
Make sure the choke levers are staying in the right spot. If that moves the secondaries won't open, nevermind the air door.
Check the vacuum levels and the step up spring. If you're not at WOT the rod hanger is still being controlled by the spring and it might not be anything close to what you need. That's normally the issue I have the biggest problem with on Tquads - that step up spring and lack of replacements.
 
The step up spring can be swapped out for a AFB/AVS spring with use of a washer to help under it. Not a fan of this. Otherwise, the cam under the step up spring is a mechanical guarantee .

The lock secondary can be wired to guarantee opening as well since the mechanical linkage can fail to perfectly operate. The choke must be open, and fully open with force to get the linkage to operate.

Would you like pictures illustrating?

Myron, I have read this since you first posted it. I'm just not quite sure of the issue at hand that you feel is lacking.
 
I agree on the choke linkage hanging up. Happened to me on a run years ago. Car came off the line like gangbusters and then wouldn't pull. The choke plate had been removed but there was still an arm on the baseplate which flipped back and locked out the secondaries. Once I wired it up, I never had the problem again.
 
Thanks for all the tips. I'll follow up on them and run them by the guy I bought the car from.

The runs themselves were all very good. I think 60' can be improved upon a bit with carb tuning and converter change. But I have to put my fresh engine in first, which should be faster. The problem only happened during the burnout. First gear was fine, I shifted into 2nd in the water and before it reved back up much, it died as if on a rev limiter or choking down a rag. The actual launch and run was fine all the way through.

What's interesting is that it apparently never happened to him when he ran the car. I put a full 3" TTI system - 1 5/8"-1 3/4" step headers, X-pipe and Dynomax Bullet mufflers on, along with suspension changes. The exhaust helped my Dart Sport so I put it on here, plus I needed the weight. ET's on the Aspen didn't slow much considering we added over 150 lbs so far. So I was wondering if the change in exhaust efficiency affected the carb tune-up, mainly the secondary opening, or not opening.

With my new engine, I'll have to test again and wanted to know what to do "IF" the problem occurs with it too.
 
If something's loose in the choke it can move. It's counterweighted to fall away and let the secondaries open but it can get hung up. I lost a clip on the choke linkage many years ago and it did that to me getting on the highway.
 
Myron, did you have the secondary linkage wired to open all the time? The little lever can fall on and off very easy.
Jetting wise, perhaps the secondary may need a change.
 
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