Thermoquad tuning issue
#1435708
05/13/13 11:53 AM
05/13/13 11:53 AM
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Joined: Jan 2003
Posts: 3,719 Space Station #5
471Magnum
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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?
-Jim
I can fix it... my old man is a television repairman. He's got the ultimate set of tools... I can fix it.
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Re: Thermoquad tuning issue
[Re: 471Magnum]
#1435712
05/15/13 10:03 AM
05/15/13 10:03 AM
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Joined: Nov 2003
Posts: 5,048 Atlanta Indiana
Dave Watt
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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.
Last edited by Dave Watt; 05/15/13 10:06 AM.
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Re: Thermoquad tuning issue
[Re: krep76]
#1435715
07/04/13 10:57 AM
07/04/13 10:57 AM
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Joined: Jan 2003
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471Magnum
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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.
-Jim
I can fix it... my old man is a television repairman. He's got the ultimate set of tools... I can fix it.
Currently Mopar-less
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Re: Thermoquad tuning issue
[Re: 471Magnum]
#1435719
07/06/13 11:15 AM
07/06/13 11:15 AM
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Joined: Jan 2003
Posts: 1,793 Windsor, ON, Canada
Diplomat360
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Posts: 1,793
Windsor, ON, Canada
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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)
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Re: Thermoquad tuning issue
[Re: Rug_Trucker]
#1435720
07/08/13 07:03 AM
07/08/13 07:03 AM
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Joined: Jan 2003
Posts: 6,410 nielsville, minn.
quickd100
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nielsville, minn.
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Quote:
Quote:
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
Air doors? Plural? What sizes?
My tunnel ram with 2 850 thermoquads. I made 18 dyno pulls dialing the carbs in. The same setup on my pumpgas 605 Hemi makes 853hp, 818ftlbs. and get 10mpg driving it nice.Dave
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Re: Thermoquad tuning issue
[Re: MY340]
#1435722
07/08/13 10:58 AM
07/08/13 10:58 AM
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Joined: Jan 2003
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471Magnum
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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.
-Jim
I can fix it... my old man is a television repairman. He's got the ultimate set of tools... I can fix it.
Currently Mopar-less
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Re: Thermoquad tuning issue
[Re: quickd100]
#1435725
07/10/13 08:42 PM
07/10/13 08:42 PM
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Joined: Jan 2003
Posts: 1,793 Windsor, ON, Canada
Diplomat360
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Windsor, ON, Canada
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Quote:
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
Hmm...so you avoid having the vacum signal fluctuations of a big cam affecting the metering circuit.
OK, makes sense, but how do you deal with the low vacum situations where you do not have WOT and yet the circuit should be running rich? I think this would happen just about any time you are going from cruise to power situation and maybe not quite yet dipping into the throttle to cause the mechanican lever to raise the rod tree.
For what it's worth I'll give this a try today...I'm curious...
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Re: Thermoquad tuning issue
[Re: Diplomat360]
#1435726
07/10/13 09:18 PM
07/10/13 09:18 PM
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Joined: Jan 2003
Posts: 3,719 Space Station #5
471Magnum
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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.
-Jim
I can fix it... my old man is a television repairman. He's got the ultimate set of tools... I can fix it.
Currently Mopar-less
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