Gremlins in the Thermoquad ? and vacuum circuit, HELP!

[Don Frelier]

What kind of plugs did you use? If you put in Autolites I would'nt be sure about them.
Did you run it much between the plug replacement and carb rebuild?
A bad valve would not give you oil consumption. But with a rebuild it's not a likely candidate.
It should run real smooth and it should idle at 700 no problem.

 

[Charlied]

What kind of plugs did you use? If you put in Autolites I would'nt be sure about them.
Did you run it much between the plug replacement and carb rebuild?
A bad valve would not give you oil consumption. But with a rebuild it's not a likely candidate.
It should run real smooth and it should idle at 700 no problem.

Not not much at all used champion RJ12YC. I know these Mopars are notorious for fouling plugs, so the new ones were put in (pain in the butt) just before rebuilt carb installed.
Again the only real issue is a slight rough idle, nothing major. Puzzled that with timing adjustment it doesn’t smooth out and vacuum only marginally improved (17).
Thinking maybe I just can’t get the mix screws right.
Starts fine and smooth @ 2-3000 rpm.

 

[Woodruff Carbs]

Here’s how I set my mixture screws if I don’t have my O2 tapped in. If you pull the 3/8 pcv hose off the base of the carb at idle and the rpm raises and maintains: you are rich. If you pull it and it immediately dies:you are lean. The ideal reaction should be a 100-200 raise in rpm momentarily, then the engine should stumble and die out.

 

[Charlied]

Great tip, I’ll give it a go. Thanks much appreciated.
It shouldn’t be that tough to get it right, but it seems I always over analyze or complicate things.

 

[72sunroof]

3 things about the thermoquad I learned
1st the well seals need to be sealed with JB Weld Marine, it handles the heat and ethanol.
2nd the shafts can leak a lot of air. I bushed mine and it made a world of difference.
3rd float levels matter
If your mixture screws do nothing as you put them all the way in you have 1 of those issues.

 

[rumblefish360]

Thanks, I’m use to the older early system I think, where there is nothing g between the valve and the port. Or is my equipment missing something

YES...the EGR valve is closed idle and opens when the EGR carb port is exposed to vacuum AND If the EGRs thermal vacuum valve, located in the vacuum line, is above its setpoint value. When this thermal vacuum valve is closed, it inhibits the EGR valve from opening (cold engine conditions - like cold start up). EXHAUST GAS RECIRCULATION (EGR) adds a controlled amount of exhaust gas to the intake fuel charge to REDUCE combustion chamber temps by introducing an inert gas (CO & CO2) to limit or reduce the thermal NOx (oxides of nitrogen) generated IF the combustion chamber temps exceed ~ 1600° F., at the instant of combustion. EGR basically criples the HP produced by the engine at the trade off of cleaner air. The fuel-air-inert gas mix requires more ignition advance to light off the mixture. Chrysler's early EGR systems were fixed orifices, directly under the carb, tapped ihto the exhaust crossover passage in manifold floor.....a horrible example of stop gap engineering.
BOB RENTON

 

[Charlied]

Great tip, I’ll give it a go. Thanks much appreciated.
It shouldn’t be that tough to get it right, but it seems I always over analyze or complicate things.

Sorry for the delay in response, been dealing with some personal issues, but everything is OK.
Did the test , carb performed well, pulled the hose, RPM moved up slightly, then stumbled and died. Restart and condition the same. Thinking I’m wrongly accusing Thermoquad of problem. Think just maybe an ignition problem, weak spark to one cylinder, distributor cap cracked ( doubt it) bad wire, poor connection to cap or plug. Will test tomorrow see what I can find. BTW did a compression test recently, all good. If I’m missing something let me know. Convinced is something simple, my biggest problem is I over complicate things. Thanks for listening

 

[Charlied]

3 things about the thermoquad I learned
1st the well seals need to be sealed with JB Weld Marine, it handles the heat and ethanol.
2nd the shafts can leak a lot of air. I bushed mine and it made a world of difference.
3rd float levels matter
If your mixture screws do nothing as you put them all the way in you have 1 of those issues.

Hunch thermoquad not the issue ,a gremlin in the ignition system the bad actor, testing that trail, wish me luck !

 

[72sunroof]

Hunch thermoquad not the issue ,a gremlin in the ignition system the bad actor, testing that trail, wish me luck !

Just dealt with my bulkhead connector from my alternator melting, bypassed with #10 wire and a #14 fuseable link from output to the starter relay. My dying while hot issue stopped.
Honestly, people dismiss the thermoquad because it is complicated and they don't want to be bothered learning so they throw it under the bus. My favorite tale tale is that the plastic warps, utter garbage. Never seen it happen and I have bought some rough thermoquads.

 

[rumblefish360]

I had one warp on me. The engine for very hot!
Fixed it myself. Sand paper of a flat surface, rub TQ until it’s even again.

Love those TQ’s!

 

[383man]

YES...the EGR valve is closed idle and opens when the EGR carb port is exposed to vacuum AND If the EGRs thermal vacuum valve, located in the vacuum line, is above its setpoint value. When this thermal vacuum valve is closed, it inhibits the EGR valve from opening (cold engine conditions - like cold start up). EXHAUST GAS RECIRCULATION (EGR) adds a controlled amount of exhaust gas to the intake fuel charge to REDUCE combustion chamber temps by introducing an inert gas (CO & CO2) to limit or reduce the thermal NOx (oxides of nitrogen) generated IF the combustion chamber temps exceed ~ 1600° F., at the instant of combustion. EGR basically criples the HP produced by the engine at the trade off of cleaner air. The fuel-air-inert gas mix requires more ignition advance to light off the mixture. Chrysler's early EGR systems were fixed orifices, directly under the carb, tapped ihto the exhaust crossover passage in manifold floor.....a horrible example of stop gap engineering.
BOB RENTON

I remember the EGR jets in the lower part of the intake so it actually had some EGR at idle which I also thought was stupid. And I believe that was only on the 340 eng in 73 from what I remember. I agree completely with everything else you said about the EGR system. Some used to say EGR is the poor mans octane booster since it cools the cylinder and lets you run more timing since the inert gas wont lite off and it cant start another flame front and cause detonation. Ron

 

[Charlied]

Thanks for the advice. FYI pulled and replaced the plugs prior to reinstall rebuilt carb. They all were dry (thankfully) but showed heavy fouling since carb had internal leak ( bad o rings). Will re-check for spark, but think it is ok. Will recheck compression as well, but would think if a cylinder bad the roughness would be more pronounced and some indication of oil consumption seen, none evident.Also when motor @ say 3000 it’s smooth.
The motor was rebuilt long time ago, re bored .30 over, crank cut and balanced, new cam nothing radical ,hardened valves, etc. shop did a great job. I’ve put maybe 5K miles on it since then. Thinking I just don’t have the touch to set mix screws properly or There is a small vacuum leak that I can’t find. Maybe I’m just too critical and comparing it to my 2017 Durango, fuel injected of course which is smooth as glass, not a fair comparison.Just for the hell of it will try to find some no ethanol gas as see what happens. I remember the days of Sunoco 260 and Hi test Amoco which were great fuels.
Thanks for the advice.
Charlie

 

[Charlied]

Problem solved, returned to golden rule : Use the damn
KISS METHOD ! Checked the cap and one tower had corrosion, happened to be #7. Pulled the plug, yup,fouled little or no spark. Replaced cap, plug. Bingo starts right up and when warm idle smooth no twitch. $15 fix.
I wrongly accused the thermoquad, it was never the issue.
Now need to bleed the brakes to re-center the proportioning valve and I’m done for now. Yeah I know it never ends but that’s OK.

 

[Charlied]

Hi Dave, finally had time to work on it yesterday. Increased timing as suggested and saw only marginally improved vacuum (17) and slight roughness still there. Tested EGR, works properly. Rechecked all other vacuum lines and connections, tight no leaks. Puzzled why timing adjustment only marginally boosted vacuum and minimum ( if any) elimination of slight roughness. Did my best to lean out the carb as well. Don’t know where to go from here. Think I need the Mopar/Thermoquad/ignition whisperer here in ATL to work the voodoo. Frustrated.

 

[Charlied]

Hi Dave, finally had time to work on it yesterday. Increased timing as suggested and saw only marginally improved vacuum (17) and slight roughness still there. Tested EGR, works properly. Rechecked all other vacuum lines and connections, tight no leaks. Puzzled why timing adjustment only marginally boosted vacuum and minimum ( if any) elimination of slight roughness. Did my best to lean out the carb as well. Don’t know where to go from here. Think I need the Mopar/Thermoquad/ignition whisperer here in ATL to work the voodoo. Frustrated.

 

[Tim Ziegler]

A scope... just for the hell of it

 

[Charlied]

Problem solved. I get the dumb *** award. Wrongly accused the TQ of the problem, it never was. Returned to the golden directive: The KISS METHOD. ( keep it simple stupid)
Pulled each wire at the cap and the tower for one ( #7) showed some corrosion. Pulled plug, yup fouled little or no spark. Installed new cap and plug ($15 fix) and bingo starts right up and when warmed up steady, smooth idle with no twitch. Keep it simple! Thanks for all your help,appreciated.

 

[Charlied]

My timing light ( vintage like me ) died yesterday. Out of town next few days on it next week. Confident that’s the fix.Let you know.
Thanks

 

[Tim Ziegler]

You got a PRECIOUS car Charlie. Gray, black viny top, factory sunroof, R. Runner hood... I'm dreamin

 

[Charlied]

Problem solved. Returned to the basic golden rule, The KISS METHOD (keep it simple stupid)
Pulled each wire @ cap and one tower showed corrosion (#7) pulled the plug, yup fouled heavy, so little or no spark. Installed new cap and plug ($15 fix). It starts right up and when warm idle is smooth and no twitch.
I wrongly accused the Thermoquad of the problem, never was. So the lesson ( seems to be hard for me) keep it simple ! Thanks for your help,appreciated.
Now bleed the brakes to re-center the proportioning valve and I’m done, at least for now!