1970 Hemi Carb Issue - Guru's?

[Hemibird]

Hey Folks ... I have been "Lurking" Here for years, and have gleaned some very valuable information. Thanks. BUT, this is my first post, and it is due to a strange issue that has popped up ... literally. I'm hoping someone with mre experience than I can Answer this.

The car - 1970 Hemi Roadrunner 4-Spd

The issue - There is a solenoid on the primary carburator(Back One), that lifts up to make contact with the throttle linkage, increasing to engine RPM. I'm assuming it it part of the automatic choke system. The solenoid expands fine, and when I pull the power wire, it contracts down, BUT, while powered, it never shuts off, causing the engine to race. I have backed off the contact screw ... only to have the solenoid expand further, and backed off more, and it expanded even further. Now, that idle adjustmen linkage screw, is backed all the way out, and the solend stays fully expanded when hooked up. Is there a sensor somewhere, or is it contained in the solenoid ... that allows this unit to function properly? My 68 Hemi has a manual choke, so this piece is non-existant on that car, therefore I can not compare or swap out parts to diagnose the probem.

Thanks in advance

 

[67 coronet]

not sure on the dual quad hemi set up,but those solenoids are normally for the ac.kicks the idle up a bit because of the draw of the ac comp at idle.

 

[Hemibird]

not sure on the dual quad hemi set up,but those solenoids are normally for the ac.kicks the idle up a bit because of the draw of the ac comp at idle.

Well ... since no Hemi came with A/C ... that isn't the application ... BUT ... Yes, the function is to kick up the idle, but it never releases, and the longer the car is driven, the higher the idle gets. I disconnected it when the idle was getting into the 2500 RPM range. I was able to maintain highway speed without stepping the on the gas, unless I was going up hill.

 

[Meep-Meep]

This solenoid is most likely has the same purpose as the one on the 440 6 BBL setup. It's an anti dieseling device. The solenoid will have only two positions: Full out with 12V and fully retracted at 0V. Try screwing the brass plunger in and see if there is some adjustment. Seems to me my 440 6 BBL is adjustable.

To properly adjust, you would set the idle speed screw on the carb body so that the throttle blades don't stick in the bores but not open ver far - not enough to allow a normal idle. Then use the screw over the solenoid plunger to set idle. When powered off the throttle closes to choke off the air supply, thus preventing dieseling.

- - - Updated - - -

Oh, and nice cars by the way. I know someone who has the exact same RR! Same guy owns the purple hemi Cuda seen in the back ground.

 

[Hemibird]

This solenoid is most likely has the same purpose as the one on the 440 6 BBL setup. It's an anti dieseling device. The solenoid will have only two positions: Full out with 12V and fully retracted at 0V. Try screwing the brass plunger in and see if there is some adjustment. Seems to me my 440 6 BBL is adjustable.

To properly adjust, you would set the idle speed screw on the carb body so that the throttle blades don't stick in the bores but not open ver far - not enough to allow a normal idle. Then use the screw over the solenoid plunger to set idle. When powered off the throttle closes to choke off the air supply, thus preventing dieseling.

- - - Updated - - -

Oh, and nice cars by the way. I know someone who has the exact same RR! Same guy owns the purple hemi Cuda seen in the back ground.


View attachment 146038

OK thanks. I'll play with it later today. My concern is, that whatever input that causes the plunger to expand, is not functioning properly. The plunger never retracts while the car is running.

That blue 70 is a Hemi 4-Sp Also? They only made 44 Coupes I think. Didn't know there were "Twins" out there.

 

[Meep-Meep]

It's not supposed to. The sol is always hot to maintain the idle. When you shut the car off the plunger retracts to slam the throttle closed and that prevents dieseling.

I think his is a HT. ..As a matter of fact I can see the absence of a pillar through the windshield. Yours look like a HT too, so I guess you have a twin. I also just remembered I saw one at the Spring Fling MoPar show in Van Nuys CA. Also blue hemi 4 spd but don't recall if RM21 or 23.

 

[440+6]

It works just like meep said, and they are all adjustable.
Give it a bit of throttle to make sure it's popped up all the way before adjusting idle.
Then unplug it and set low idle, just enough for it to run 600-650 rpm
If it won't hold a steady idle it may be week and need to be rebuilt.

Freakin' awesome cars you got there.

Just looked at your pics again and I'm not a hemi guy but those return springs look pretty heavy, it may be fighting them.

 

[Hemibird]

It works just like meep said, and they are all adjustable.
Give it a bit of throttle to make sure it's popped up all the way before adjusting idle.
Then unplug it and set low idle, just enough for it to run 600-650 rpm
If it won't hold a steady idle it may be week and need to be rebuilt.

Freakin' awesome cars you got there.

Just looked at your pics again and I'm not a hemi guy but those return springs look pretty heavy, it may be fighting them.

Well .... I think I found the real problem ... on the other side of the engine. The choke tube was corroded and snapped down at the exhaust manifold. That plunger seems to be reacting to an improperly functioning automatic choke. Those springs are stock. I'll know for sure in a couple of weeks when I replace that tube.

- - - Updated - - -

Yea you are correct, the 70 is a hardtop ... my 68 is a Coupe. I got them mixed up. If I do it again, I'll get both the same. :head_smack:

 

[snakeoil24]

Meep is correct, this is anti dieseling solenoid.

 

[Meep-Meep]

Well .... I think I found the real problem ... on the other side of the engine. The choke tube was corroded and snapped down at the exhaust manifold. That plunger seems to be reacting to an improperly functioning automatic choke. Those springs are stock. I'll know for sure in a couple of weeks when I replace that tube.

- - - Updated - - -

Yea you are correct, the 70 is a hardtop ... my 68 is a Coupe. I got them mixed up. If I do it again, I'll get both the same. :head_smack:

Fixing the choke tube is just good GP to keep thing working but has nothing to do with the choke. Adjust the solenoid as instructed.

 

[coloradodave]

What he said...both times.

 

[Hemibird]

Fixing the choke tube is just good GP to keep thing working but has nothing to do with the choke. Adjust the solenoid as instructed.

OK ... Choke tubes are fixed, and carbs rebuilt. Solenoid still not functioning properly. Guess I need to get a new/rebuilt one.Thanks for the advice guys.

 

[440+6]

In your 1st post you said it would pop down when you unpluged it, and if it pops back up when you plug it back in I would say it is functioning properly.

It should always be in the up position when the key is in the start or run position, and pop down when you turn the key to the off position.

Why do you think it's not working?