Thermoquad idling issues

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Leaking fuel wells & leaking o rings are two different problems & have different symptoms.
Leaking FW:
- IF the lower gasket [ base to bowl ] is intact, idle is unaffected but you get a rich off idle.
- if this gasket is broken where it seals the throttle bore, then fuel will seep into the bores & cause a rich idle.

Leaking o rings:
- will cause rich idle & generally rough running, depending on how bad the leak is.
 
mopar says to remove vac spring from vac bar, adjust metering screw till the bar is close to top of carb well. now the bar will move with throttle blade, vac cannot affect anymore. btw set the bar at wide open throttle . my TQ has never had vac spring in it. just food for thought
 
Well, I'm not going to argue, but the metering rods certainly DO have an effect on the idle circuit. And with that, I am done on this thread. Good luck with it.
 
Removed carb and set transfer slots a little over square. Replaced o-rings with some viton 3/8 1/16 thick. Reinstalled carb and it runs good at 2 turns out on the idle mixture screws now but still pig rich at idle. And hard to do a hot restart without holding throttle halfway open, then comes the plume of smoke. There is a whistle at idle and I found it coming from the primary shaft on the passenger side. When shutting the car off I get a few drips from that same shaft location.

The shaft doesn’t feel like it has excessive play at all. But all the Teflon coating has been removed by the company that reman’d it.
Also the box said it was a 6138s but after measuring the primaries and looking closer at the half ground off number it’s for a 440 stationary engine. A 6518s Thermoquad. I doubt that has anything to do with the rich idle. There is zero drips from the boosters when running. I took a video but need to figure out how to post it.
 
Do people drill out the air bleeds on Thermoquads to clean up the idle or just drill the primary butterflies?
 
Met rods can ONLY affect idle if the boosters are dripping fuel & that is because the met rods are part of the main [ jet ] cct. And if the boosters are dripping fuel, then the carb has a major problem: flooding, or pri blades open too far at such that the main cct is activated.
 
[1] Whistle at idle. Some carbs do it, nothing wrong or anything to worry about.
[2] T slot close to square & mixture screws 2 turns out? Turning the screws in should stall the engine. If not, the engine is getting fuel from somewhere other than the idle port + a small amount from the t slot.
[3] I have never drilled the primary side air bleeds on a TQ & do not advise it.
[4] The PCV may not be working with the low vac. I would disconnect & plug it; then re-adjust mixture.
[5] One thing that concerns me about these re-man carbs. Internal corrosion of the alum passages. A re-man TQ on another engine that I tune has a problem whereby one mixture screw has no effect: can screw it in to seat it or back it out 6 turns, nothing changes. I suspect corrosion may have blocked a passage.
 
If you have 0.040" [ or less ] of T slot showing at idle, then you do not need any [ more ] bypass air.
 


Here is a video of it running. I don’t see any fuel leaking from the booster. You can hear the whistle from the shaft. Car is idling around 900 rpm.
Yesterday I was able to kill the car with both idle mixtures screws. Today I am only able to kill it with one. The other screw does change the idle characteristics, but doesn’t kill it.
 
Did you advance the timing like I suggested in post #17? You will get a BIG surprise!
Did you read the links I posted?
Advancing the timing will increase idle rpm, without doing anything else. That will allow the blades to be closed further, & greater adjustment of idle mixture.
That cam duration is going to have some smell at idle.
 
Bewy said:
Did you advance the timing like I suggested in post #17? You will get a BIG surprise!
Did you read the links I posted?
Advancing the timing will increase idle rpm, without doing anything else. That will allow the blades to be closed further, & greater adjustment of idle mixture.
That cam duration is going to have some smell at idle.
Click to expand...
I haven't advanced the timing yet. I will try that tomorrow. Seems like most people run around 16-20 for a daily driver. I am not sure how well the car will start with 30 degrees at idle. I just have the stock electronic ignition with no start retard. The blades are already just about closed enough to completely cover the T-slots. I have read the links you posted. Some smell at idle is alright, but when you back up at night and see thick exhaust smoke in the headlights, that doesn't seem normal.
Could you make out the smoke coming out of the exhaust in the video?
 
toypar said:
Do people drill out the air bleeds on Thermoquads to clean up the idle or just drill the primary butterflies?
Click to expand...
Demonsizzler used to make this modification to his “Racing TQ’s” only for the serious racer. The thing is, you really don’t need to do this on most engines. He used Holley parts to get this done.

The primary butterfly drilling is easiest and quickest way to get done what you want done. The air bleeds are more for driving down the road or track when the blades are much more open.
This is where the AFR is affected by that mod.
 
Bewy said:
Did you advance the timing like I suggested in post #17? You will get a BIG surprise!
Did you read the links I posted?
Advancing the timing will increase idle rpm, without doing anything else. That will allow the blades to be closed further, & greater adjustment of idle mixture.
That cam duration is going to have some smell at idle.
Click to expand...
I hooked a vacuum pump to the vacuum advance and advanced it to 32 degrees and the idle went up 175 rpm. I was able to back the idle screw out about 1-1.25 turns to get it to idle around 900rpm. Still have smoke coming out of the exhaust. Passenger side idle mixture screw doesn’t kill the engine when seated but the drivers side does.
When I shut the car off after idling for awhile, hot engine, I got fuel smoke or vapor rising up out of the primary aree and still have fuel dripping from the primary shaft only when turning off. Which tells me there is fuel leaking above the throttle plates somewhere. I have not been able to see any drips out of the booster when idling or when shutting off. But this has to be my rich running issue.
 
The idle rpm increased because the engine is making more HP. Exactly what was expected.
So, when you switch off the engine, fuel leaks out of the pri shaft?
That could be leaking needle & seat { unlikely } or the o rings are not sealing. After switching off the engine, shine a light down the pri bore to see if you can see where the fuel is coming from.

Did you disconnect & plug the PCV? This cam is going to need more air & fuel to idle. So the fact that the pri blades are almost closed means the engine is getting air from somewhere. Make sure the sec blades are fully seated. That leaves the PCV [ not closing off at idle & letting a large amount of air into the engine ]; or air leak
 
Bewy said:
The idle rpm increased because the engine is making more HP. Exactly what was expected.
So, when you switch off the engine, fuel leaks out of the pri shaft?
That could be leaking needle & seat { unlikely } or the o rings are not sealing. After switching off the engine, shine a light down the pri bore to see if you can see where the fuel is coming from.

Did you disconnect & plug the PCV? This cam is going to need more air & fuel to idle. So the fact that the pri blades are almost closed means the engine is getting air from somewhere. Make sure the sec blades are fully seated. That leaves the PCV [ not closing off at idle & letting a large amount of air into the engine ]; or air leak
Click to expand...


So, this engine wants 32 at idle. Fair enough. Even using manifold vacuum (he can’t use ported or it won’t matter and we both know that) he will still have a hard time getting the rest of the curve in shape.

This is an example of needing a programmable ignition. He’s going to have a hard time not having too much timing at peak torque. I guess that depends on what the curve needs to be without the extra timing at idle.

This is one of the hardest things to build a curve for. You can’t get the timing low enough at peak torque even when the vacuum drops.

He may be better off at 26 or so initial, no vacuum and tune the curve up and then see what he can get with the vacuum hooked up.

Now I’ve forgotten what the original engine is…
 
Ok, 340. Most likely it won’t want over 35 at the most. Running 32 at idle even with vacuum is going to make the curve hard to get. Especially without knowing what the can pulls and when.
 
I think 32* initial is way to much unless your going to run it locked out and with - a programable ignition - excellent idea Newbomb. This seems to be way out there kind of thing for most guys but MSD has a distributor for this. Works with or without a vacuum advance hose hooked up.
 
Post# 44, 45 & 46. Nope, not hard to get 32* at idle. OP can stick with his 12* initial [ static ] timing & add 20* with man vac adv. He can then choose the centri curve he wants. There is more than one way to do it....
A 440 that I dialled in recently has a sizable cam in it, M1 single plane intake & 850 TQ. It idles with 42*, 32 init [ locked dist ] & 10* added with MVA.
 
post number 15 holes between rede lines are idle by pass air passage, may not be open

carb with holes.jpg
 
Bewy said:
The idle rpm increased because the engine is making more HP. Exactly what was expected.
So, when you switch off the engine, fuel leaks out of the pri shaft?
That could be leaking needle & seat { unlikely } or the o rings are not sealing. After switching off the engine, shine a light down the pri bore to see if you can see where the fuel is coming from.

Did you disconnect & plug the PCV? This cam is going to need more air & fuel to idle. So the fact that the pri blades are almost closed means the engine is getting air from somewhere. Make sure the sec blades are fully seated. That leaves the PCV [ not closing off at idle & letting a large amount of air into the engine ]; or air leak
Click to expand...
I pinched off the pcv hose and the car wanted to die.
 
Newbomb Turk said:
Ok, 340. Most likely it won’t want over 35 at the most. Running 32 at idle even with vacuum is going to make the curve hard to get. Especially without knowing what the can pulls and when.
Click to expand...
The can starts advancing at 12 inches of vacuum. This engine makes 9-10 at idle. The distributor was set up by FBO. He set it up for 18 initial and 34 all in. Advance adds around 14
 
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