I still like my Thermoquads, but....

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Bill Crowell

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I'm still emotionally and financially invested in my Thermoquads, but did you ever notice that if your TQ-equipped Mopar sits for awhile, the carb won't work right? The vehicle keeps running out of fuel. It will run fine for a minute or two, then die from lack of fuel, and then start back up again after a few minutes and do the same thing.

So far I have found two reasons for this:

1. Fuel inlet (float) valve stuck or obstructed due to residue left by our crummy gas; and

2. Top cover of the carb has loosened up so the carb idle circuit isn't pulling vacuum.

3. (?) Idle circuit obstructed by crummy gas residue.

Would anybody have more reasons that I should check out? I really need to be able to fix this when it happens!

Can I clean out the idle circuit without pulling the carb by removing the idle adjust screws and spraying carb cleaner in there?

Or is it time for me to disassemble and clean my TQ?

Kindly edumacate me on this guys. Thanks a lot.
 
Put a Holley Street Demon on it. They are the modern day Thermoquad. I love mine.
 
Will those carbs pass smog in California? I don't think so(?). The TQ was the original type of carb on the vehicle and complies with smog. Even though this Mopar is a 1978 model, it needs to pass smog here in CA every 2 years (isn't that ridiculous?), and pretty much everything needs to be stock for it to pass.

Besides, you've just got to accept the fact that some of us are real diehard TQ fans. Now excuse me, but I've got to get back to banging my head against the wall.
 
Will those carbs pass smog in California? I don't think so(?). The TQ was the original type of carb on the vehicle and complies with smog. Even though this Mopar is a 1978 model, it needs to pass smog here in CA every 2 years (isn't that ridiculous?), and pretty much everything needs to be stock for it to pass.

Besides, you've just got to accept the fact that some of us are real diehard TQ fans. Now excuse me, but I've got to get back to banging my head against the wall.

The Holley Street Demon IS a modern TQ. They do not appear to be CARB certified. Sorry you have that limitation. That sucks.

Street Demon 1901 625 CFM 4 Barrel Carburetor, Polymer Main Body
 
It's only a low-compression 440 anyway, Rusty, so it's never going to be any powerhouse, no matter what carb I use. Plus the TQ has great advantages because it's what I've already got and it's paid for.

And when a TQ works right, it works quite well.
 
Dont forget, the crap fuel that plugged up your thermo quad will clog up any replacement carburetor as well.
 
It's only a low-compression 440 anyway, Rusty, so it's never going to be any powerhouse, no matter what carb I use. Plus the TQ has great advantages because it's what I've already got and it's paid for.

And when a TQ works right, it works quite well.

Oh I absolutely love them, but the Carter tuning kits for them are ridiculous. Seen some in the 500 dollar range. cough cough hack hack.
 
It's only a low-compression 440 anyway, Rusty, so it's never going to be any powerhouse, no matter what carb I use. Plus the TQ has great advantages because it's what I've already got and it's paid for.

And when a TQ works right, it works quite well.

And I don't know about "never going to be any powerhouse". You can do a lot to wake them up. Especially if you want to pull the timing cover.
 
What sucks is you could put modern catalytic converts and a modern carburetor, have way cleaner emissions than when new and fail because its not the 42 year old worn out stock stuff it came with unless its CARB approved, which is a costly process.

Today's fuel is not crap, its designed for evaporative emissions and fuel injection. It lights off in a heartbeat which sucks for a carburetor as it's meant to be in a contained system not subjected to atmosphere.
 
Will those carbs pass smog in California? I don't think so(?). The TQ was the original type of carb on the vehicle and complies with smog. Even though this Mopar is a 1978 model, it needs to pass smog here in CA every 2 years (isn't that ridiculous?), and pretty much everything needs to be stock for it to pass.

Besides, you've just got to accept the fact that some of us are real diehard TQ fans. Now excuse me, but I've got to get back to banging my head against the wall.

Ah yes, the commiefornia smog laws.... My truck is a '92 gmc and it barley passes smog. One thing you could do is keep the smog legal thermoquad and buy something that has more power potential for having fun. Then, whenever you need to get it smogged, switch the carb so it passes. Alternatively, just have an intake manifold-carb setup you can just switch out. :usflag:
 
Just keep it bone TQ stock and it should pass. If it doesnt, fail it twice and get it fixed on the states dime as a gross polluter. TQ's should pass if they are in good shape as well as a smogger 440. I put a NOS carb on my 82 mazda and it blew cleaner than my 96 EFI Breeze. I'd check your EGR valve on that 440, guaranteed bad. it should NOT be open at all at idle or at WOT. My mazdas was opening at idle and I was able to adjust it to stay closed (it had a threaded pintle, some don't. I cranked it down 2 turns) a little longer off idle and it completely cleared up a rough idle.

Today's fuel does suck. Its down on power (diluted with methanol) , down on life expectancy (more hygroscopic) and is still expected to be used in open systems such as lawnmowers and generators. It even attacks some older fuel system components as well as using a food source that could be used for famine relief. Our flex fuel E85 van gets 70% of the mileage it gets on 'regular' gas (E10 here in CA) and my lawnmower and weed wacker wont start after 3 weeks of sitting unless I scrape the white jello out of the jet. They should sell 100% dino gas like they do red diesel for off road/ small engine use only in bulk, not the $18/gallon you pay for it in quart bottles at Home Depot.
 
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What sucks is you could put modern catalytic converts and a modern carburetor, have way cleaner emissions than when new and fail because its not the 42 year old worn out stock stuff it came with unless its CARB approved, which is a costly process.

Today's fuel is not crap, its designed for evaporative emissions and fuel injection. It lights off in a heartbeat which sucks for a carburetor as it's meant to be in a contained system not subjected to atmosphere.

It's actually better performance wise, because alcohol has a higher octane than gasoline. It IS crap though, in the sense it doesn't last as long and breaks down FAR sooner than non ethanol fuel.
 
It's only a low-compression 440 anyway, Rusty, so it's never going to be any powerhouse, no matter what carb I use. Plus the TQ has great advantages because it's what I've already got and it's paid for.

And when a TQ works right, it works quite well.

Don't forget to back off the timing too if you have it advanced. That will help it pass.
 
I called up an experienced mechanic friend of mine, who owns a smog and repair shop. He used to work on TQs, but likes to avoid them now. He gave me 4 tips to maybe get the TQ working again without disassembling it for cleaning:

1. Get the engine started and when it starts to die, spritz some carb cleaner into the TQ to confirm that it dies because it is starving for fuel.

2. If you don't already have some there, insert a length of rubber hose into the fuel line between the fuel pump and the carb. Clamp the rubber line and run the engine until the carb runs out of fuel. Then release the clamp. The inrush of fuel pressure into the vacuum will often dislodge any blockage at the float valve.

3. Get it running at about 1,000 RPM and then suddenly block off the carb air horn until the engine dies. This will sometimes clean out a plugged idle circuit.

4. Tap the carb all around with the handle of a hammer.
 
It's actually better performance wise, because alcohol has a higher octane than gasoline. It IS crap though, in the sense it doesn't last as long and breaks down FAR sooner than non ethanol fuel.

Its crap for a carburetor that sits in atmosphere. I've dealt with it, had to clean my pressure washer carb after it sat all winter. I live with it just like everyone else with an old vehicle. Its a ***** if you don't drive it every day.

I used to have a job where we intentionally vaporized gasoline and conveyed it to an engine. I've personally driven the CARB city and highway dyno runs hundreds of times, have been to a CARB certified facility, have multiple patents on the subject, worked with a PHD in Chemical Combustion, dealt with winter and summer fuel. Tested "up to" E10, E15, E85, and Indolene (which is what they use for certification). I've had that golden tar lab tested to see what it is (its basically very low octane jelly). Bottom line is, it is what it is, it does what it does, and you do what you can with a carburetor. But I have 11 year information so maybe that magic changed.
 
It's actually better performance wise, because alcohol has a higher octane than gasoline. It IS crap though, in the sense it doesn't last as long and breaks down FAR sooner than non ethanol fuel.
Only if your motor is set up to use higher compression to exploit the higher octane. If not, its wasted.
 
Find a way to run it out of fuel when you park it. Shut off the supply and let it idle until the bowl is dry. Next time it will crank a while but should run the same as when you parked it. Stupid California gas.
 
Don't forget to back off the timing too if you have it advanced. That will help it pass.
even timing is monitored in CA, if its not within 1 of EPA sticker timing, it will fail and test only stations wont take the 10 seconds to back the distributor off to proceed as its illegal. If NOx is high, its EGR related, if the HC is up, its combustion related. Methanol (HEET) in the tank helps with HC levels. We suck........I tell you Rob, its the most unfriendly classic car state in the union with their SMOG laws, yet there are thousands of 2 stroke STIHL leaf blowers in use every day here and you can smell them 50 yards away as they blow their nasty 2-stroke smoke. But trying to get that segment of the workforce to clean it up with newer expensive SMOG regulated equipment somehow "disproportionally affect a certain class of workers"...I though we were a classless society?
 
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Bill,
Stick with the TQ. Whatever is wrong with it can be fixed. And fixed easily.
A loose air horn will NOT affect idle.
Your problem may not be the carb at all. Could be a blocked filter, dirt in the tank, water in the fuel, tank venting. All these should be checked out.
If the above doesn't fix the problem, get an overhaul kit. These carbs are easy to work on, but do NOT forget the two screws inside the choke tower!!
There are two O rings that sit in the black body that can leak over time. They cause richness & rough idle, stalling.
Another area to check is the underside of the black body. There are two 'pods' under the pri jets that are epoxied to the body. Occasionally they deteriorate & leak, causing rough running. Test them for leaks by putting some fuel in the bowls & holding up to eye level & looking for leakage. If they leak, they can be re-sealed by removing the old epoxy & using new epoxy.

I would NOT use the new Holley/Demon TQ copy. They are poorly made...& designed. Great risk of dropping a circlip into the bore when changing m. rods. Mate tried one & could never get rid of the bog....Holley tech dept was useless.
 
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