Thermoquad blues

[PursuitSpecial]

I've been tinkering with the Thermoquad on my Gran Fury for a few months now trying to get it to perform at least comparably to my Holley 84014, and it just comes nowhere even close. I can't even get it to make the trademark moan when the air door opens. The carb is a model 9365 for a 1981 318 truck, so the only difference between it and my original carb is the lack of the O2 feedback solenoid. I tried all the tuning tips in the direct connection manual. It has #1966 rods, .149 secondary jets, and I bored out the spray bar and accelerator nozzle. It has the secondary vacuum brake to roll the air door open and prevent bogs. The carb runs great otherwise, no bogs or backfires, idles and accelerates perfect, it just has no power and won't make the sound I want. And slowly leaks all the fuel out in about 2-3 days. The car feels like a slug and won't even chirp a tire like it will with the Holley. My dad is a carburetor expert but he refuses to touch TQs because of the poor fuel atomization and tunability, but I'm determined to get it to work just for the trademark bluesmobile sound. I put the carb on my HP 400 77 Gran Fury and it still doesn't make the sound. When the air door opens on it, it goes so lean it starts skipping and fluttering and once it finally opens, it just runs in place, but I attribute that to running a small block carb on a big block, throwing the calibration off. I don't get it. I'm running the richest jets the carbs ever came with and the engine is still starving for fuel and not flowing enough air to make noise. I'm starting to think there's an inherent handicap in the later 80s carbs or something. I've got a 74 model large bore TQ I'm building, if it doesn't make noise there must be something else afoot.

 

[Camtron]

I still have yet to get my hands on a TQ, and I figure you already know but there’s like 20+ adjustments that all have to be done in specific order/procedure to come close to desirable results…I went 625 Street Demon when I did my 4barrel swap. you get the sweet sound from the secondaries opening and they’re super easy to tune, lol

 

[Aspen500]

IIRC, there's 21 adjustments. If adjustment #6 is off, adjustments 7-21 will be off (for example). Way back when, the TQ always seemed to work fine,,,,,,,,until someone messed with the adjustments (kind of like the Ford VV carb was). I do remember the TQ having the problem of the plastic mainbody warping and leaking air or something similar. It was 40 years ago so the memory is a bit hazy.

 

[M_Body_Coupe]

...I can't even get it to make the trademark moan when the air door opens. The carb is a model 9365 for a 1981 318 truck...It has #1966 rods, .149 secondary jets, and I bored out the spray bar and accelerator nozzle...The carb runs great otherwise, no bogs or backfires, idles and accelerates perfect, it just has no power and won't make the sound I want...

Ahh yes, that "whhhhaaaaaa" sound eh?

So here is the thing, for a 1-3/8" primary carb this is probably way too rich to start off with.

Stock that carb had a 0.097" primary and 0.110" secondary jets with a 2359 rod, which is: 0.072 - 0.054 - 0.045 stepping, while your 1966 rods are: 0.067 - 0.052 - 0.045.

Therefore even with a matching power step of 0.045", that new 0.149 secondary jet is sizes and sizes larger!

However, that probably doesn't have any bearing on the lack of the sound. So I'm curious: do you actually get the secondaries openning up when you blip the throttle wide open with the car just at a stand-still (i.e. no moving, just in sitting there)?

I would want to make sure there are NO bindings of any sort in your throttle linkage and that the TQ settings actually let the carb fall in-line with what the engine's air flow demand is like.

For what it's worth, take a look at my 'Carter TQ Library' dump here => darcio.no-ip.org/mopar/carter_tq/Carter_TQ_Library-Aug_2024.zip

That's everything I have on the mightly TQ, good amount of reading, including various original Carter published service manuals, so do a little bit of a digest and you'll be in a great position to troubleshoot the issue further!

 

[PursuitSpecial]

Yeah, the secondaries work fine. You can floor it briefly out of gear and they roll open, but no sound. The stock jets in the carb were ludicrously lean, it would bog even when gradually tipping into the secondaries and backfire if you nailed it. I've read most of the literature out there, and made all of the adjustments exactly as written in the book "Super Tuning Carter Carburetors" using the data for a 340-360 carburetor. The carburetor works fine now. It doesn't bog, backfire, or stumble. It works great just for normal driving like I do 99% of the time, but WOT is just underwhelming, it hits the kickdown and still just struggles to gain RPM with no noise. I don't really care about horsepower or acceleration though, just the sound when you hit it. I know the engine is capable of doing it, my grandpa drove the car for 20 years and used to comment on how when you would pass someone it would sound like it's sucking the hood in while it runs in place. He had 2 different carbs on it through its life, the original one that it came with, model 9372 and a replacement he had put on it in 1990, model 9014, an early big block carb. I suspect something is different about the truck carburetor I have on it now. The only other thing that could be wrong is maybe an airflow problem with the engine, when the carburetor was changed, the throttle position sensor and vacuum transducer on the kick panel computer were never hooked back up, meaning he drove the car for 14 years and over 100k miles at base timing, which appears to have deposited a thick, shiny crust of carbon soot in the intake and could be restricting the engine.

 

[Ele115]

Are you trying to use a non Lean Burn carb on a Lean Burn engine? If so, I would correct that situation first. The timing and carb work together on those

 

[Aspen500]

A longshot idea here. You said the intake is crusted in the ports, have you seen the back of the intake valves and bowl area? It's possible the valves are caked thick with carbon and restricting air flow. I ran into that many times over the years at work. Might be worth a check anyways.

 

[Ele115]

It's not "always the carburetors fault" either. Timing advance and the basics but you dont have the correct carb for one thing. Just do a basic on it and see what you find. Timing light, vac gauge, plugs, spark quality and verify quality and correct application of your parts. Come to think of it, you can't do much about your timing advance so just check base timing and timing chain.

 

[GTX JOHN]

149 is a very rich jet for most combo.

Even a small change in "Spray bar" of a few thousands really
changes the carb richer as well and has never worked for me.

 

[PursuitSpecial]

Timing isn't an issue, I replaced the original ESA distributor and computer with MSD and new plugs when I started driving it. It has a mechanical advance with 16 degrees at idle and about 40 maximum. I have a borescope so the next time I pull the carb I'll have a look at the valves.

 

[Ele115]

OK so this is no longer Lean Burn. It's in the carb or engine (likely) Wouldn't hurt to check compression, fuel delivery and vac, but that's up to you. I thought you had mentioned Lean Burn. Anyway, good luck.

 

[M_Body_Coupe]

Timing isn't an issue, I replaced the original ESA distributor and computer with MSD and new plugs when I started driving it. It has a mechanical advance with 16 degrees at idle and about 40 maximum. I have a borescope so the next time I pull the carb I'll have a look at the valves.

Honestly, I do not want to sound like an all-knowing "guru", or everyday jerk, but it is very hard to square up your "...timing isnt' an issue..." and "...about 40 maximum..." remarks.

So here is the thing: SB Mopars, especially the open chamber heads, need extra advance (in comparison to the closed chamber stuff) but 40 deg isn't it!!! Normally the best power is around 35 deg...and "around" means +/- 1-2 degs at most.

If you are genuinely running with 40 TOTAL mechanical advance I would be willing to put money on detonation being an every day thing.

Anyways, not quite sure what you were expecting as far as advice goes, but you pretty much have an answer for just about every suggestion so far, and that answer appears to be "nope, that's not it".

Yeah...kinda hard to work with that, you know?

 

[kkritsilas]

I also am no expert, but isn't 16 deg. at idle a little much? Isn't it normally at 8-12 deg. at idle? And yeah, 35-36 deg. at about 2500 rpm with the vacuum advance pulled and plugged? All assuming a close to stock engine, of course.

 

[SRTMirada]

The secondaries won't open if the choke isn't completely off. Make sure that you have the engine warmed up and the choke is fully open.

 

[AHBguru]

The secondaries are vacuum operated. If you have the air door adjusted correctly, it'll open up at WOT and draw fuel, creating the sound we all know and love. On the TQ in particular, there are two things that affect secondary air door operation: the choke and the choke vacuum kick. If the choke is working properly, there should be absolutely no play in the valve. If the vacuum kick is bad or misadjusted, that will also mess up secondary operation. Check the choke thermostat, test the vacuum kick, and make sure it's all adjusted properly. I don't think it is. I think that choke is closing under load, making it run stupidly rich, and locking out the secondaries.

On that note, since the engine is carboned up that bad, it has to come apart. It's gummed up, and will soon blow itself up with that much sludge and gunk in it. At the very least, pull the heads, hot-tank everything, and start over. Replace the timing chain while you're in there. If the cam and lifters are fine, leave them be. New cams and flat tappet lifters are of rather poor quality. Run what's in there.

When you're finished doing all that, re-jet the carb so it cruises at 18:1 ATFR. Yes. Really. TQ's were designed to run super lean. Leaner is meaner, and also extends the life of the engine. Or would've, anyway.

Ignition - there's no power in ignition. Ditch the MSD junk, and get a regular Mopar electronic ignition kit, which uses a single pickup, so set the base timing for 7-9°BTDC, total mechanical advance at 33-35° BTDC, and all-in (with vacuum) at least 55° BTDC at 4000 RPM. Set the curb idle for 650 RPM, and fast idle for 1200 RPM. Run Autolite or NGK copper plugs, good 7 or 8 mm resistor wires, and double check your coil. You must run a ballast resistor with the Mopar kit. Never run it on the street without vacuum advance.

Air cleaner - run a regular dry filter. Find a Mopar dual snorkel air cleaner, one with air horns at 9 and 4. Or find a 340 air cleaner. Use the flexible hose from the main air horn over to the factory CAI tube (it runs down under the battery, and comes out behind the front license plate). You can remove the rubber shield at the front end there, for a little extra sound.

 

[PursuitSpecial]

The choke has been disabled, it's wired open, there's no need for a choke in this area, even in January a few pats on the gas is sufficient to keep it running. The only car I have that has a functioning choke is the Aspen. The vacuum brake works properly from my testing and I've even tried disabling it entirely to allow the secondary to fly open as it likes and it still doesn't make noise. I tried retarding the timing back 5 degrees, no change in performance or sound but I will keep it there to preserve the engine, even though I don't think an 8:1 engine on 93 is going to severely detonate just from a few degrees of timing, but there is always moderate undetectable damage that can occur. If I were after lean mixtures and high advance curves at cruise without compromising power I definitely wouldn't choose a thermoquad, my dad experimented with the old Holley mile-dial system that allows you to control the mixture with the turn of a knob and a MSD timing control that allows you to advance or retard timing on the fly and water/methanol injection to curb detonation under load using a knock sensor to keep it in safe parameters. He was able to get relatively high mileage out of a 440 pulling loads. Even better, use port fuel injection. Putting a dedicated lean secondary jet in the carb is just going to kill the power for the sake of mileage. Lean mixtures have no effect on spark knock, but rich mixtures can only decrease detonation and preignition. I have observed that experimentally with the aforementioned devices. BTW, when I was running the 84014 Holley with a nice fat secondary jet and a power valve, it got better mileage than the factory spec thermoquad as well as performing much, much better. The engine isn't carboned up to the point it needs a rebuild, it runs flawlessly, burns no oil, has good pressure and doesn't make any unusual noises despite having 175k on it. I'm not about to rebuild an engine to make a carb happy. I'll try steam-cleaning the valves with water and if it doesn't help, it's not a dirty engine problem.

 

[AHBguru]

The choke has been disabled, it's wired open, there's no need for a choke in this area, even in January a few pats on the gas is sufficient to keep it running. The only car I have that has a functioning choke is the Aspen. The vacuum brake works properly from my testing and I've even tried disabling it entirely to allow the secondary to fly open as it likes and it still doesn't make noise. I tried retarding the timing back 5 degrees, no change in performance or sound but I will keep it there to preserve the engine, even though I don't think an 8:1 engine on 93 is going to severely detonate just from a few degrees of timing, but there is always moderate undetectable damage that can occur. If I were after lean mixtures and high advance curves at cruise without compromising power I definitely wouldn't choose a thermoquad, my dad experimented with the old Holley mile-dial system that allows you to control the mixture with the turn of a knob and a MSD timing control that allows you to advance or retard timing on the fly and water/methanol injection to curb detonation under load using a knock sensor to keep it in safe parameters. He was able to get relatively high mileage out of a 440 pulling loads. Even better, use port fuel injection. Putting a dedicated lean secondary jet in the carb is just going to kill the power for the sake of mileage. Lean mixtures have no effect on spark knock, but rich mixtures can only decrease detonation and preignition. I have observed that experimentally with the aforementioned devices. BTW, when I was running the 84014 Holley with a nice fat secondary jet and a power valve, it got better mileage than the factory spec thermoquad as well as performing much, much better. The engine isn't carboned up to the point it needs a rebuild, it runs flawlessly, burns no oil, has good pressure and doesn't make any unusual noises despite having 175k on it. I'm not about to rebuild an engine to make a carb happy. I'll try steam-cleaning the valves with water and if it doesn't help, it's not a dirty engine problem.

We've given you the advice you've asked for. You've got the car so jerry-rigged, and you're obviously determined to use the holley, so put the dumb thing on there and run it. I see no need for any of us to assist further.

 

[Ele115]

Uncle Tater says thar aint a dagggum thang wrong wid er excepn' it aint makin that thar wah whooomp sound y'know? I'm fixxin a put about 68 degreees advance in 'er and go haul corn squeeezins