Been trying to get my thermoquad tuned in on my stroker small block and it’s been giving me some fits.

Previously, I had a 6166 model (72 400) with the primary jet opened up to 101 and the stock 5137 secondary jet and 1938 rods. Also, the squirter was opened up a bit (don’t recall exactly how much). Ran really well, but pretty rich at WOT. Never had a wideband O2 on it though to get any readings.

Body on that carb cracked, so I replaced it with a 6322 off a 73 440 truck. I swapped the primary jets, rods and squirter from the 6166, but used the smaller 5125 secondary jets from the 6166.

At that time, I also installed my wideband O2.

The carb pretty much performs the same as the 6166 did, but it’s a bit lean at under light steady part throttle acceleration. It’ll bog slightly when the transmission upshifts. Very rich at WOT (10:1). Dead nuts on at idle and steady cruise.

It’s largely unresponsive to adjustments of the step-up screw. Started with a one turn up from bottomed, and have added as much as an additional full turn.

Played around with different jet at rod combinations from the two carbs, without much improvement.

I figure I can make a secondary air door adjustment to get the WOT back in line, but I want to figure out that part throttle issue first. I’m thinking maybe I need to take a look at the step-up spring, but I figure the two carbs would have the same spring. Or maybe I need to go back to the larger secondary jets, but I really don't think they should be coming into play at part throttle.

Any thoughts?

Nothin' from nobody?

What's the practical adjustment limit on the step-up? How far should I be turning that screw before I need to be looking elsewhere for a problem? Just to try to get a reaction, I gave the screw another full turn and it seemed to help the cruise. Still fat as heck under heavy load.

It sounds like just the secondary door is adjusted a little too loose..try tightening it up a bit, maybe a half turn at a time...

That's easy enough to try, but I'm thinking the opposite on the secondary side. It's rich under full throttle with no bog on heavy throttle input. When I initially calibrated, if anything I set it tight.

Does the 10.0 Air/Fuel ratio stay steady during a WOT run, or does it straighten itself out after a few seconds?
Without being there to tune on carb myself, it sounds like the secondary air door adjustment which is giving you the problem. I agree with tightening it up a bit to see if it makes a difference.
If it's set way too light, it will open fast and just keep pouring fuel in.
Don't go more than 4 full turns of the air door screw from the resting position, otherwise you can break the spring.

Sounds like I have the same problem at the moment. I've got everything else dialed in except it runs rich at WOT. I've disconnected the secondary linkage to see if I could isolate the problem and it is still running 10:1 with just the primaries at WOT. Were you able to fix the issue with yours?

I have a factory 46 page service book from Chrysler on the thermoquad. I will scan it an upload it...great info. Do you have the c-4152 tool for adjusting the air valve adjustment plug? You should still be able to order it from Miller tools.

http://www.mediafire.com/download/t7d9tgfh9i0kt9h/82TBOGBOOK.pdf pdf

It's not perfect yet. Still a little lean under light part throttle acceleration. Done quite bit of tweaking to the air door, pump shot and step-up piston. Can't say that there was any one thing that made a major difference.

One issue I know I've got is with the step-up piston. Needs a lighter spring. Carb goes really fat when I lift on coast down.

To fix your rich WOT condition, I'd set the stop on the air door to open just a bit more. That will lean things out in hurry. Tweak it about 1/16" to 1/8" at a time.

Good to hear you haven't given up, what jet and rod combo are you running?
I'm not sure adjusting the air door stop will have any effect on my situation. I've disconnected the secondaries to isolate this issue on the primary side. I'm going to wire open the choke next just to make sure it isn't effecting it in any way.

They can be VERY sensitive to air door opening. Try adjusting it in .050 increments. My 528 Hemi on the dyno picked up 55hp by adjusting the air doors just .050. Dave

Jim,

Where are you overall with your tuning effort?

I ask because most recently I had made some progress on getting my 9800 series to idle (had everything to do with getting the idle air bleed sized 'just-right' for my combo). Now the next step is to really get into the bigger picture and try to have a decent cruise/power AFR.

I'm using the Innovate LM-1/LM-1 RPM Covnerter combination. Here is where I started off:

O2/RPM chart


O2 stats


RPM/O2 chart


RPM stats


....after a rod change (2110 to 1996) and air bleed change from the stock 0.065" to 0.037" here is what I ended up with:

O2/RPM chart


O2 stats


RPM/O2 chart


RPM stats


What I am curious about is what are the actual AFR to aim for? 14.7 is stoich...OK, but beyond that I read/hear that our performance motors will run 'best' slightly richer...so maybe around the 13.5-14 ballpark figure, and somewhat richer under WOT...but where?

In short, I'm wondering what is everyone using as the 'aim/goal' in their tunning efforts?

BTW: A shameless plug to our little F/J/M body forum, here is the direct URL to the full writeup on this => Dippy.org TQ Tuning Post (M_Body_Coupe)

Cutting coils off the spring will make it shorter. It doesn't lighten the spring rate.

I've got a couple of springs. Colors are different, but dimensions appear to be the same. I might try trimming one of them.

I found that tuning with a very long duration cam was easier if you discard the spring entirely. My cam is 288/292@.050. Engine runs and idles much better now. Dave

Dave,

That's what I did years ago with a 300 duration solid cam in a 340 and it worked the best for me too.

I believe removing the step up spring is somewhat akin to plugging the power valve on a Holley. I'm running an XE275HL cam. I don't think it is quite so radical that it should require ditching the spring.

hi, the metering rod bar rides on a lever that's connected to throttle shaft, it will move the bar up as you open the throttle. mopar said years ago, to do that so carb would idle and lack of vacuum would not cause mixture problems, after doing that open the throttle and see how far the bar moves up, then adjust it accordingly. its a very simple setup.best bet is to buy the book on carter carbs.