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TR2/3/3A Auxillary carb return spring in "More BS about TR,s"

karls59tr

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Does anyone have a better picture, or maybe a sketch of this setup? It's on pg 16 of Bob Shaller's pamphlet on Triumphs. I can't quite make out what's been done to the connection at the throttle shaft in the picture. Looks like maybe some kind of vertical rod attached to the shaft?
 

Geo Hahn

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Looks like the extra arm is brazed to the throttle shaft.

Are you looking at an original paper copy or an online scan or such (i.e. would a better pic help?
 
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karls59tr

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Looks like the extra arm is brazed to the throttle shaft.

Are you looking at an original paper copy or an online scan or such (i.e. would a better pic help?

I'm looking at an online version of the picture in the paper copy. So I need to braze say a 1&1/2" rod on to the shaft,drill a hole for the spring and fabricate a bracket that bolts to the air cleaner,correct? I've never done any brazing but I will give it a shot. The reason that I'm interested in this mod is that I'm having issues getting the idle to return to normal. I've read the posts on the various causes of this in a recent thread and I've done the required fixes with no luck. What worked for awhile was attaching a spring from the front of the throttle shaft to the horn bracket but still having issues of return to idle. I should mention that I have a fast road cam installed so I'm not sure the stock idle of 850 is appropriate? I get a steady idle at 1000 rpm but after a drive the idle wants to stay at 1500 rpm which seems a little too high. The 3 runs well enough and plug checks show tan colored plugs so I thought I'd try the center return spring set up. Any thoughts?
 

TR3driver

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Strange, p16 of my copy if "More BS" deems to be all cylinder head stuff. I don't see anything about an extra throttle return spring.

I question the wisdom of adding tension to that shaft anyway. It will put even more force on the front bushing, increasing wear and making the problem even worse.
 

CJD

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It’s been a while since I read that book, but ISTR the aux spring going vertically from the linkage. The result was reduced load on the shaft while ensuring a consistent idle. The stock link puts a side load every time you open the throttle. A well positioned linear spring would counter and reduce that load.
 
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karls59tr

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Strange, p16 of my copy if "More BS" deems to be all cylinder head stuff. I don't see anything about an extra throttle return spring.

I question the wisdom of adding tension to that shaft anyway. It will put even more force on the front bushing, increasing wear and making the problem even worse.

My mistake. Page 22...Fig.16
 
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karls59tr

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It’s been a while since I read that book, but ISTR the aux spring going vertically from the linkage. The result was reduced load on the shaft while ensuring a consistent idle. The stock link puts a side load every time you open the throttle. A well positioned linear spring would counter and reduce that load.

I wonder if I could just hook a spring from the shaft "coupling" to the heat shield I have put on?
 

TR3driver

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OK, I found it. It does look to be brazed to the shaft, but I think a copy of the front clamp-on lever would also work.

I've fought problems with returning to the set idle myself, found issues all the way from the nylon bushings in the firewall binding when they get hot, to wear in the bellcrank pivot allowing it to drag on the bolt head, to wear in the linkage pivot balls causing them to bind only at idle.

But the most common, for me anyway, is wear in the front shaft bearing/bushing allowing the throttle plate to drag on the bottom of the bore. That has been my main motivation for rebushing carb bodies twice now, and both times it made the problem disappear.
 

charleyf

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The part that will suit your needs is called a Throttle Linkage Arm. You can buy these at several sources such as SPEEDWAY MOTORS. Part number 910-18400 std. ( $10) or 910-18410 Lite. This unit clamps onto the rod with set screws so no brazing is involved. You can cut off any excess length that you don't want. In your case you can vary the tension of the spring by the length of the arm or the size of the spring. As for a bracket to hold the other end of the spring you only need a small hole for the end of the spring to fit into. Like maybe the edge of the air cleaner.
Be sure to check the diameter of your rod and get the appropriate size arm to fit that.
 
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karls59tr

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The part that will suit your needs is called a Throttle Linkage Arm. You can buy these at several sources such as SPEEDWAY MOTORS. Part number 910-18400 std. ( $10) or 910-18410 Lite. This unit clamps onto the rod with set screws so no brazing is involved. You can cut off any excess length that you don't want. In your case you can vary the tension of the spring by the length of the arm or the size of the spring. As for a bracket to hold the other end of the spring you only need a small hole for the end of the spring to fit into. Like maybe the edge of the air cleaner.
Be sure to check the diameter of your rod and get the appropriate size arm to fit that.
Thanks for the info.:encouragement:
 
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