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Roy M's Avatar
 
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Location: Cumbria, England
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Throttle linkage adjustment

Inspired by a couple of recent posts I decided to check if my throttle was opening fully with the pedal to the floor - had about 3/8" left before the stop so now want to make the necessary adjustments.

My question is fairly simple - where do I start and am I about to open a can of worms?

From previous posts it looks like I adjust from underneath (at clutch housing) to get to full throttle but (and here's where I don't know the geometry of the linkage) it strikes me that, apart from taking up any slack I am likely to simply move the bottom (for want of a better word) position and have an increased idle speed. the only way I can see me gaining a greater travel is if I somehow increase the length of a linkage (if you see what I mean)

From the previous posts a lot of you have done this, some with idle problems and some without - can anyone help here?

Car is an '88 Carrera and it looks like I'm going to have to change my servicing garage as this should have been picked up for the price I paid (and they should be able to adjust front wheel bearings but that's anothr story)

Thanks for any help
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Old 09-17-2002, 12:58 AM
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You didn't say how you determined that the throttle wasn't opening all the way but you should be the one pressing the pedal to the floor while someone else watches the gap. A little movement at the pedal when it is close to the floor makes a big difference at the throttle. (I missed 1/2" of throttle travel once because I had my sweetie press the gas to the floor.)

Under the car on the left side of the transmission you'll find a bell crank (2 levers connected on the same shaft). One lever is connected to a stiff wire that goes rearward and up to the engine. You disconnect this wire from the bell crank and turn the wire counter clockwise to make the linkage longer. If it doesn't want to turn, you must loosen a jam nut on the engine end of that wire first.

-Chris
Old 09-17-2002, 01:35 AM
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Chris

I jammed the throttle to the floor with a length of 2 x 1 and am sure it was fully down.

Not sure how this will come out but if I extended A only then I haven't changed the arc and would end up with the same amount of throttle travel further up the scale - ie idle up but full throttle at the top end - to get the adjustment I was hoping for I would need to make B smaller to increase the arc of the throttle travel. Is this the adjustment you're talking about?

Throttle
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O C (Pivot)
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| B
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Old 09-17-2002, 01:54 AM
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I had exactly the same problem on my 89 Carrera and simply took out the slack but adjusting the balljoint a few turns which connects to the bellcrank under the transmission. At full throttle I've now got around 1mm between the stop on the throttle body and the arm. Idle speed was unaffected. So was performance, unfortunately.
Old 09-17-2002, 02:21 AM
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Quote:
Originally posted by Roy M
Chris

I jammed the throttle to the floor with a length of 2 x 1 and am sure it was fully down.

Not sure how this will come out but if I extended A only then I haven't changed the arc and would end up with the same amount of throttle travel further up the scale - ie idle up but full throttle at the top end - to get the adjustment I was hoping for I would need to make B smaller to increase the arc of the throttle travel. Is this the adjustment you're talking about?

Throttle
|
|
|
O C (Pivot)
|
| B
|
__________________
A
I was afraid you had used a 2x4 or something to jam the throttle down. That method is not very reliable IMO.

I understand what you are saying about just moving the range up or down. While either side of the throttle linkage could be shortened, I'm just used to shortening the one going up to the engine because I remove that linkage when I drop a motor (to keep it from getting bent).
-Chris

The throttle linkage should be adjusted so their is a little (2-4mm?) slack at the bell crank to wire linkage joint. When this is so, you should have full throttle opening as well.
Old 09-17-2002, 06:19 AM
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Mark Wilson
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Roy,
I first adjusted the bellcrank by the tranny. That took the slack out but the idle speed went up. I then disconnected the linkage at the throttle body and lengthened it slightly. Cured the high idle and had full travel.
Mark
Old 09-17-2002, 06:30 AM
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Thanks for the replies - I'll give it a go tomorrow and let you know how I got on when I get back from the Le Mans classic!!

Cheers
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Old 09-17-2002, 06:34 AM
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I have been needing to do this myself, but I work best with pictures (ala Pelican CD).

Does anyone have any pictures of their actual linkage and which items get adjusted?

Thanks
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Old 09-17-2002, 06:49 AM
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Hi guys,

I just did this yesterday as mine was off by about 1 inch from reaching wide open throttle. I believe the correct way to adjust this linkage to provide wide open throttle is by disconnecting the ball cup at the end of the throttle cable coming from the pedal/front of the car. It will just pop off the ball connected to the pivot. Caution some newer cars have a pin that holds the cup to the ball. Loosen the stop nut on the cable (screw it forward and then turn the ball cup in the same direction to shorten the length of the linkage. You may want to make an adjustment and then reconnect it and check the throttle position again. Then re-adjusted more if needed.

I believe that if you tighten the other side of the linkage by shortening the wire that goes up to the linkage at the engine that will fix the wideopen throttle issue but also increase your idle speed. Now with all this said, the linkage can be adjusted in 3 or 4 places and each has an affect on what happens to wide open throttle, idle speed and length of throw. If some of the other points have been adjusted incorrectly than it affects all the other distances and adjsutments.
Old 09-17-2002, 08:11 AM
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Roy,

You may also want to check your Full Throtle Switch. If it isn't operational your car will never know to go full rich.
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Old 09-17-2002, 09:25 AM
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Before attempting adjustment of your linkage ... I would recommend replacement of the two plastic bushings at the pedal bellcrank and transaxle bellcrank! After 14-15 years ... they are probably worn beyond reasonable limits, and another reason for excessive throttle linkage play!
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Old 09-17-2002, 09:29 AM
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Early S - Do you have a link to these parts on Pelicans website? I am still looking for some pictures of this so that I can visualize what I am doing.

Thanks
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1989 911 Carrera Coupe 3.2
2012 BMW 135i M Sport
"It is not how much power you have, it is how much you have left to spare!"
Old 09-17-2002, 10:06 AM
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How much HP did I lose?

Well I was inspired as well!!!

Just went and looked at mine, I had almost 1/3 travel on the Webers that wasn't being used!

How much HP do you think I was leaving on the table with only 2/3 - 3/4 throttle on an SC motor?
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Old 09-17-2002, 11:50 AM
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Now I'm interested as well. Wayne, I think this calls for a Technical Article. Think of all the throttle bushings, bell cranks and throttle pedals you'll sell!
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Old 09-17-2002, 11:59 AM
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