Lean Burn Carb Idle Problems-Help Needed

77newyorker440

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Hey guys,
I am in need of your all's help and knowledge. The New Yorker is at Carlisle and is having some idle/driveability issues. It just started on this trip up but got progressively worse today.

Here is the problem: When you just slightly tap the gas, it stalls out completely. Sometimes you can get through the bog and get into the higher rpms, in which it runs pretty perfect. But anything in that range of slightly off idle kills it. This makes driving through Carlisle very hard, and I do not want this problem to get worse. The car has the original Lean Burn and Thermoquad set up, and I have never tuned or messed with it.

My guess is that perhaps the idle is too low? I don't have a test light with me, but the engine seems really shakey. Someone recommended for me to get a coil, so I will try that tomorrow but I am not sure if it will work.

Only another problem is that it is having a lot more issues with hot starts than it used to. The only changes from before (when it started nicer) are headers, valve covers, and experiencing heavy rain for the first time.

Thanks in advance for your help,
77newyorker440
 

CBODY67

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Sounds like an internal carb issue not related to the ELB system. As if the accel pump is not working all that it should or one of the internal fuel passages is not letting the transition fuel work as it should, in the transition between the idle system and the main system. Might be a vac leak somewhere, too, possibly.

MIGHT even be a load of highly-ethanol'd fuel, too! Like E15 or higher, rather than just "normal" E10.

For good measure, scope out some deals on a Mopar Perf electronic ign kit (or similar) and a Street Demon 650cfm elec choke carb. Then, those two things could put things back like "before ELB" with no intake manifold change. BUT for now, I wouldn't automatically conemn the ELB completely.

Just some thoughts,
CBODY67
 

Davea Lux

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First off, I don't think your coil is the issue. A bad coil will cause the engine to run progressively worse as more load is applied by increasing RPMs. Check the coil wire to be sure it is fully seated. Check the throttle position sensor to be sure it is not loose or disconnected.
It mostly sounds like your accelerator pump has bit the dust. Take the top off the air cleaner and see if you get a squirt of fuel as the throttle is moved, if it does not squirt, that is probably the issue. You might also want to check the fuel filter to be sure it is not full of crap and starving the carb for fuel.

Check those things and report back.

Dave
 

Love Shack

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I have a lean burn set up with a Thermoquad on my 79 road runner. I had similar issues. Bad accelerator pump. Rebuilt the carb, and the hard hot start issue was caused by a bad thermostatic choke control. It still had some ‘spring’ to it, but not like a new one. If you can’t find one for the Thermoquad, find one that looks similar and will bolt on, one for a two barrel application. You just need to swap out the rod from your old one. After the carb rebuild and choke replacement, mine runs like new. Be very careful to rebuild carefully to specs. Thermoquads can be fussy, but when set up right, are great. Good luck.
 

77newyorker440

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Sorry for the long wait, it has been a very busy few weeks, but here is the update.
The carb somehow fixed itself on the drive back to the hotel from the fairgrounds on Saturday evening, but in order to be safe, my dad and I sent the carb to @Dana for a rebuild.

However, I still have a question. Where is the idle adjustment screw on the Thermoquad. Most YouTube videos showed it being a silver screw being above the fast idle adjustment screw. However, I have no screw or screw hole there, so how would you adjust the idle? Is idle fully controlled by the Lean Burn Unit?
Thanks,
77newyorker440

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Davea Lux

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The lean burn controls have nothing to do with the fast idle on this application. The thermostatic choke control mounted at the base of the carb on the passenger side of the carb controls the movement of the choke which in turn moves the cam that controls fast idle. A lot of these cars idled too fast because the spring in the choke control was weak/corroded from age and did not fully release the choke. A lot of techs back in the day also set up the idle too fast so that the engine would not die when the car was placed into reverse.

Dave
 

polara66hardtop

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I suspect you need to rebuild that carb. My 77 Cordoba did the same thing. There are numerous places for vacuum leaks, mainly the O-rings. Find a competent rebuilder, I did mine and now it runs perfect.
and never use ethanol on thermoquads, the rubber in them don't like it.
 

77newyorker440

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Okay, so this brings up an interesting point. I do have that bracket, but my A/C solenoid appears to not work. When you turn on the A/C, the idle drops around 100-150, instead of raising. Also, as I said before, I am having the carb rebuilt, but, since this car is a daily driver, I, unfortunately, cannot avoid ethanol due to my location (no local non-ethanol gas).
 

CBODY67

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Premium doesn’t have ethanol. Kim

If so, considering that ethanol is an octane enhancer, then what is used to get the octane to the higher levels of Super Unleaded/Premium gasoline?

Just curions,
CBODY67
 

CBODY67

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Okay, so this brings up an interesting point. I do have that bracket, but my A/C solenoid appears to not work. When you turn on the A/C, the idle drops around 100-150, instead of raising.

The solenoid is that to "kick" the throttle speed back up with the a/c compressor operating. In some cases, the solenoid is not powerful by itself to raise the rpm, so sometimes it took a slight tap of the throttle to get the rpm to increase, by observation. Not sure if any replacement solenoids for the TQs are available any more.

What you might do is to find the idle speed specs for a non-solenoid TQ for your engine size. Use that as the hot base idle speed with the a/c compressor operating, then see where the idle rpm goes when the compressor is turned off. If it is too high, when the ignition is turned off, the engine will not die immediately, but try to keep running. Decrease the idle rpm until this does not happen. Might well end up in the 700-750rpm range, which would still have plenty of rpm with the a/c compressor working and the shifter in "D". Might need to tweak it a bit to see what works best for your vehicle.

Just some thoughts,
CBODY67
 

77newyorker440

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The solenoid is that to "kick" the throttle speed back up with the a/c compressor operating. In some cases, the solenoid is not powerful by itself to raise the rpm, so sometimes it took a slight tap of the throttle to get the rpm to increase, by observation. Not sure if any replacement solenoids for the TQs are available any more.

What you might do is to find the idle speed specs for a non-solenoid TQ for your engine size. Use that as the hot base idle speed with the a/c compressor operating, then see where the idle rpm goes when the compressor is turned off. If it is too high, when the ignition is turned off, the engine will not die immediately, but try to keep running. Decrease the idle rpm until this does not happen. Might well end up in the 700-750rpm range, which would still have plenty of rpm with the a/c compressor working and the shifter in "D". Might need to tweak it a bit to see what works best for your vehicle.

Just some thoughts,
CBODY67
That is an interesting idea, my car use to run after turning the ignition off, but that stopped a few months back without any tuning or changes to the carb.

When I get the carb back, I am planning on doing a full tune up and when I do that, I will test your idle idea.
Thanks,
77newyorker440
 

CBODY67

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Before the higher base idle speeds of the 1970s, due to emissions issues, "dieselling" was pretty much unheardof. But with the higher idle speeds, it became more prevalent. Still, not supposed to do it. Some used the same a/c idle solenoid (wired to the ignition system rather than to the a/c compressor) to set the hot base idle with, then when the ignition was turned off, the solenoid retracted and the engine stopped as it should.

CBODY67
 

Slap Stick

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If so, considering that ethanol is an octane enhancer, then what is used to get the octane to the higher levels of Super Unleaded/Premium gasoline?

Just curions,
CBODY67
Ethanol isn't used strictly for raising the octane. It is used as an oxygenate to reduce emissions. As side benefit is raising octane so fuel that uses ethanol has a lower octane before the ethanol is added.
Non ethanol premium uses chemicals to raise the octane, just like all fuels. Straight gasoline is very low octane before the octane enhances are added.
And saying premium fuel is ethanol free is only true in some areas. In many areas ALL gasoline has ethanol.

It sounds like the problems on the OPs car cleared up after leaving the area, so it must have been the fuel used in that area. There are so many formulations of gas depending on area laws it "bottles" the mind.
 

CBODY67

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It sounds like the problems on the OPs car cleared up after leaving the area, so it must have been the fuel used in that area. There are so many formulations of gas depending on area laws it "bottles" the mind.

Another observed complicating factor is that not all states have laws requiring the pumps to state the ethanol content of the gas being purchased.

Enjoy!
CBODY67
 
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