Wierd throttle issue?

[1BAD68]

My Charger runs great and everything but here's the issue...
When giving it gas from a stop, if I slightly push on the pedal it works fine but anything more than a slight gradual push and the thing takes off.
It lurches forward to the point that if I am turning a corner, the tires spin. Its actually embarassing because it looks like I'm trying to show off or something.
Once it does its initial "lurch" then it works fine.
Its a 318 with a Edelbrock 600 Performer carb.
I went through the linkage several times over and there is no binding and you cant feel it in the pedal so I'm starting to think its a problem in the carb, maybe accelerator pump?
Any ideas?

[John_Kunkel]

Does that Edelbrock carb have the correct Mopar throttle lever extension? (Edelbrock #1481) Without it the linkage/cable position and ratios won't be correct.

[1BAD68]

No it doesn't have the Edelbrock #1481 part but it has worked fine for the last couple years without it.
Here's another symptom that happened yesterday...
getting on the freeway I punched it and got up to 65 then let off and throttle was stuck at 3200 rpm. I kept kicking the pedal but it was still stuck.
Was able to get off the freeway and slowed down fine until the transmission decided to downshift to 2nd gear, I'm standing on the brake going sideways around the corner tires smoking.
Pulled over and shut it off, popped the hood and the throttle cable was pulled back in its hold down bracket about a 1/4 inch.
I have figured out the problem but just for fun, maybe you guys can figure it out?

[elacruze]

Broken motor mount?

[1BAD68]

Yup thats it, drivers side.

[b5blue]

Along with through bolted engine mount one of these welded to the K frame will stop that from happening, I'm glad you are safe!   

[elacruze]

Yup thats it, drivers side.

YAY I win!! 

I love playing 'Telephone Diagnosis' !

[Al]

 

[68X426]

I was going to say you must have used some Toyota parts!

It would have been funny months ago.


Thank you for passing on info about this. 

[greenpigs]

Does that Edelbrock carb have the correct Mopar throttle lever extension? (Edelbrock #1481) Without it the linkage/cable position and ratios won't be correct.

Mine works fine without it also, or appears to. Is it something you think i should add?

[elacruze]

This may turn into a threadjack, but hey...

Throttle lever extensions are for drivability. There is a ratio between the distance your throttle pedal travels and the amount the throttle plates open. This ratio accounts for how smoothly the throttle reacts to your foot, and plays into how easy the car is to drive and control. Your engine build, driving style, rear axle ratio, torque converter, flywheel weight etc. all play into drivability as well so every car is different. If you don't have the lever extension, buy it or make one to try out and see if you like the change; a lot of people suffer with less-than-optimum drivability because they don't know it can be a lot better. Consider also the angle at which your cable pulls the lever off idle. The closer to 90* your cable is at idle, the more progressive your pedal will be.
Drivability has been one of my bread-and-butter areas for a very long time; I bought $1000 worth of European throttle bodies for my build for no reason other than that they have a progressive throttle linkage instead of a simple lever or cable snail like all the American throttle bodies. Drivability to me is paramount, and I have never failed to find some business tuning somebody else's car after they drive one of mine.
Matching all your components with your goals is important, everybody knows that. But what we often fail to see is that our actual use is often a lot different than our vision was, and that a few minor adjustments and compromises to our original goal can make the car a lot more fun to be in a lot more often.

[greenpigs]

It may not be about the original subject but its still related and for about $9 worth trying.

[John_Kunkel]

The throttle usually works OK without the extension but the TP linkage needs it to maintain the correct lever ratio.

[greenpigs]

You mean for the kickdown? I use a manual VB so I may be fine with the way it is.

[1BAD68]

Consider also the angle at which your cable pulls the lever off idle. The closer to 90* your cable is at idle, the more progressive your pedal will be.

can you explain this in more detail?

[1BAD68]

Also, why would the rubber part rip like this?
These mounts are about 6 years old.
Can I get new rubber parts or do I get the whole mount?
Any part numbers?

[elacruze]

Consider also the angle at which your cable pulls the lever off idle. The closer to 90* your cable is at idle, the more progressive your pedal will be.

can you explain this in more detail?

It's a little difficult without pictures. I'll try, and see if I can find or draw something up to illustrate.
First, understand the relationship between a few key points;

-Throttle shaft, which is the pivot axis for the throttle lever
-Throttle cable attachment point on the throttle lever
-throttle cable housing fixation point on the engine

The throttle shaft never changes its location, it only rotates.
The cable attachment point is fixed at a specific distance from the shaft.
The cable attachment point travels in an arc from idle to wide open throttle.
The cable housing fixation point does not change.

So, if your throttle cable fixation point was on exactly 180* from the cable attachment point on the lever, the line drawn from the CAP to the CHFP would pass through the TS axis. (ignore for a moment that it's obvious you wouldn't be able to pull the lever this way) When you pull the throttle cable, there is a 1 to 1 relationship between how far you move your foot and how far the cable retracts. But, CAP doesn't travel directly backwards to the CHFP, it travels about 90* to the cable travel. So it has to open the throttle more degrees of arc to accommodate the cable travel distance. At the point where the cable attachment point, the throttle shaft, and the cable housing attachment point form a 90* triangle, the lever opens the throttle plates the least amount per movement of the cable.

So, if you begin at idle with the cable end, throttle shaft, and cable attachment at 90* then you will have the most pedal travel per opening degree where you need the most control, right off idle. Further, as you open the throttle more, the relationship between the opening and cable movement acts the same towards fully open as it does off idle-the more you open, the less the cable travels per degree. This is ok, because if you're already at 1/2 or 3/4 throttle you don't need fine control the same way as you do off idle.

Please let me know if any of this isn't clear and I'll go find a diagram someplace to illustrate.

[1BAD68]

Thanks, that made sense.
So by modifying it to be at a 90 degree angle does it make a significant difference?

[elacruze]

Thanks, that made sense.
So by modifying it to be at a 90 degree angle does it make a significant difference?

The short answer is yes.

The long answer is, it depends on a huge amount of variables. To begin with, all of these angles are considered by the OEM and the aftermarket engineers before you ever see the parts; that's how they know you need an extension particular to Chrysler, to maintain something like the stock ratios and pedal feel. So, you can assume that it's already not far off of a realistic best. There is always room for individual improvement though.
Where it gets squirrely is after you add an engine/trans combination underneath the throttle that behaves in ways the engineers can't plan for. Big throttle plates open more bore area per degree of arc, letting in more air, so simply adding a larger carburetor changes your tip-in and throttle feel. Putting together a fast opening throttle, a stroker motor and low axle gears makes for a jumpy car.
Also, without some significant modifications like custom cables and brackets, you probably can't achieve a 90* position at idle anyway. You only have a limited cable travel, so you have to be sure it still opens 100% too. At a minimum, adding length to the lever reduces the pedal ratio somewhat so you'll see less sensitivity even if that's the only change you make. You can add spacers under your cable bracket, if the cable is long enough to allow that to get the cable to pull at a higher angle. You may be able to reposition the lever on the throttle shaft, or add a bolt-on lever to the shaft plate to change the starting point of the cable attachment. You just have to experiment with positions and ratios to find what works best for you and the car.

I can't let any of this pass without a word about safety; Whatever you do, you absolutely *MUST* be certain that there is no possibility of binding, holding the throttle open, hanging up on brackets, engine torque opening the throttle, or components coming disconnected while 'testing'. Your life is at stake every time you touch the throttle system, as much or more so than with any of the other systems in the car.

[FLG]

Check out Rons thread on reinforcing the motor mounts to avoid that situation.