Inconsistent idle (sort of..)

[beanhead]

Hi everyone, I have a 440 with the 274 XE comp cam and a speed demon 850 mech. carb,
initial timing is at 20° which gives me right about 36° all in, vacuum advance is disconnected at the moment...getting steady vacuum between 15/16 inches. (sorry guys I don't have a working tach right now) When the motor is fired up after sitting it makes some decent music at idle, when I get to the first stop the idle increases to where there is no real rumpity-rump...no big deal, but if I pop it into neutral and blip the throttle, the engine will return to the slightly lower idle speed again to where you can hear some cam....now, this is just a sound thing for me it has nice throttle response either way, no hesitating/surging etc---- However, I have noticed if I press on my throttle arm by hand when it's at rest, the rpm will drop a little..it IS at rest on the stops and the throttle cable is not tight..Did it before and after rebuilding/cleaning the carb. If I lower my speed with the adjuster screws, when it wants to idle lower then it's a little too low and gets a little shaky...thanks for any ideas!

 

[moparnation74]

First thing to check is your throttle return spring.....Or get a stronger spring....I would try that first before moving to something else..

 

[beanhead]

First thing to check is your throttle return spring.....Or get a stronger spring....I would try that first before moving to something else..

Thanks! I have the Lokar setup with two springs now but I wouldn't put it past them to be a little weak

 

[moparnation74]

One of my old carbs on another car exhibited the same problem and a stiffer spring corrected that. It could be something else but start simple first...

 

[dadeo]

You may want to check to see if your distributor advance spring is too light and not returning the advance all the way when you lightly get off the throttle.
Not sure how idle can drop when pressing on throttle arm if it's against the stop already.

 

[moparnation74]

He may thought it was at the stop but it may not have been....It may be related to something else but start simple first and move on....

Or with him adjusting the idle speed and the spring tension got it out of whack as well....He turned the adjuster and slowed it down but the spring didn't pull it all the way back until he popped the pedal to the floor and physics brought it all the way back...Hence, lower idle...

 

[Dennis H]

Wow, similar recent symptoms. 850 DEMON. Nice rumpity at about 750. Then intermittent hang around 1100. 2 return springs. Tore a bunch of deadening and carpeting out at the pedal to be sure. I think it was the modified lower base of the drop down air cleaner snagging the butterfly. Still not completely sure. Think I'm imagining things. When the throttle on the Coronet (manual) acts like the new Challenger (manual) on warm up, it is annoying.

 

[Yatzee]

Hi everyone, I have a 440 with the 274 XE comp cam and a speed demon 850 mech. carb,
initial timing is at 20° which gives me right about 36° all in, vacuum advance is disconnected at the moment...getting steady vacuum between 15/16 inches. (sorry guys I don't have a working tach right now) When the motor is fired up after sitting it makes some decent music at idle, when I get to the first stop the idle increases to where there is no real rumpity-rump...no big deal, but if I pop it into neutral and blip the throttle, the engine will return to the slightly lower idle speed again to where you can hear some cam....now, this is just a sound thing for me it has nice throttle response either way, no hesitating/surging etc---- However, I have noticed if I press on my throttle arm by hand when it's at rest, the rpm will drop a little..it IS at rest on the stops and the throttle cable is not tight..Did it before and after rebuilding/cleaning the carb. If I lower my speed with the adjuster screws, when it wants to idle lower then it's a little too low and gets a little shaky...thanks for any ideas!

Perhaps you have an issue with the linkage that runs down to the tranny creating binding, provided your car is automatic. Or maybe there's an issue with the fast idle cam or it's setting screw or the choke activating spring or rod. I have heard of such strange goins-on when guys remove the throttle plates from the shaft for cleaning and they are not set in right or loose. But in your case it sounds as though the stop screw is not seating consistently because of minor binding somewhere.

 

[oldbee]

Yes maybe a loose throttle plate or bent/worn throttle plate shaft? Not binding linkage on a part of int.manifold?

 

[beanhead]

Thanks for your replies everybody... I put another spring on there and it seems to drop back down to the proper RPM now at the stop lights, even after driving for awhile... it seems with the lokar setup on the demon the leverage point doesn't let the Springs exert enough pressure to pull it hard against the stop... stiffer spring now and all seems good thanks again guys

 

[Dennis H]

Thanks for your replies everybody... I put another spring on there and it seems to drop back down to the proper RPM now at the stop lights, even after driving for awhile... it seems with the lokar setup on the demon the leverage point doesn't let the Springs exert enough pressure to pull it hard against the stop... stiffer spring now and all seems good thanks again guys

Good deal. How about a pic of that spring configuration when convenient.

 

[beanhead]

Good deal. How about a pic of that spring configuration when convenient.

The Silver Spring is one I had in my toolbox...

 

[Dennis H]

Thanks, I initially went with a second spring to pass tech inspection for drag racing in Reno. It snaps back nicely so was not the source of the hang up.

 

[oldbee]

lol, OEM return spring from '68. I love these posts! It worked great on the 383 & now on the 440. I don't think these springs are the same as on firearm magazines!

 

[miller]

If I lower my speed with the adjuster screws

Just asking, okay...are you trying to adjust idle speed...at the mixture 'screws'? You set idle speed, at the idle speed stop screw.

 

[beanhead]

Just asking, okay...are you trying to adjust idle speed...at the mixture 'screws'? You set idle speed, at the idle speed stop screw.

Not using the 4-corner screws, no...the idle speed screws. I try not to fidget too much with them to keep my transfer slot openings proper. It was almost like when the throttle was on the stops, you could push on it and there was a slight amount of "flex" to the parts, just enough to make a tiny difference in RPM

 

[oldbee]

You do have a slight amount of play in throttle cable don't you?