TR2/3/3A Throttle sticks

[doc50]

I have a common problem I've tried to fix to no avail. I always need to kick the throttle down, usually a couple times in quick succession to idle down from 1200 or even higher. I've put a heavier return spring at the bulkhead, increased axial spring tension at the butterfly rods on the carbs, oiled and greased everything. Nothing seems to help.

That jus cain't be normal....

ISTR someone (Randall, was that you?) having a cure, maybe something as simple as adjusting geometry of the assy to certain angles relative to each other?

Thanks for any sage advice.

Thom
1959 TR3
#TS34909L(O)

 

[TR3TR6]

Did you check to make sure your throttle shaft isn't bent a little? That's a common problem especially after installing an engine. If you disconnected the linkage, you can then figure out where the hangup is.

 

[trglory]

You probably already checked this, but it's important to note in the general discussion that the very first thing you need to do is to make sure that the needles are centered in the jets. If you don't hear a healthy clank when you drop the pistons, you will not be able to reliably set the idle of the carbs. Once you get that squared away, you can then go about checking for vacuum leaks, rod adjustments, spring tensions and the like.

 

[karls59tr]

I ended up running an extra return spring from the front of the linkage to the area around the horn. There is a better method....Auxillary Carb Return Spring: "More BS about TR's" with a picture on Page 22. (Maybe Randall could post the picture as I believe he has a copy of the book online?)

 

[TR3driver]

ISTR someone (Randall, was that you?) having a cure, maybe something as simple as adjusting geometry of the assy to certain angles relative to each other?

I think it was more a case of running down all the problems I've seen. Most common (for me) is wear in the front throttle shaft bushing. That lets the shaft droop down just a bit when the throttle is open, which in turn causes the throttle plate to drag on the bottom of the bore. Blipping the throttle gives the plate enough force to slide along the bore and lift the shaft back up where it belongs (and also I think reduces the downward force while it is closing). But, I have also had the bellcrank pivot wear until the crank drags on it's mounting bolt; and the balls in the rod end pivots wear into a football shape that can bind just as it reaches idle.

I did a quick scan through "More BS" but didn't see anything about a throttle return spring. IMO the stock springs should be plenty and adding more springs is likely to cause other problems (like accelerated wear). Note that you can adjust the tension on the springs mounted on the carbs (but again don't go too tight or that front bushing will wear faster).

Here's the "More BS" link so you can look through yourself. I might have missed it.
https://drive.google.com/open?id=0B2H2NJt34OffMmE1YTU0YzctMTQyOC00MmJmLWFiZGItNTI5ZjI3N2NjZTIy

 

[karls59tr]

I think it was more a case of running down all the problems I've seen. Most common (for me) is wear in the front throttle shaft bushing. That lets the shaft droop down just a bit when the throttle is open, which in turn causes the throttle plate to drag on the bottom of the bore. Blipping the throttle gives the plate enough force to slide along the bore and lift the shaft back up where it belongs (and also I think reduces the downward force while it is closing). But, I have also had the bellcrank pivot wear until the crank drags on it's mounting bolt; and the balls in the rod end pivots wear into a football shape that can bind just as it reaches idle.

I did a quick scan through "More BS" but didn't see anything about a throttle return spring. IMO the stock springs should be plenty and adding more springs is likely to cause other problems (like accelerated wear). Note that you can adjust the tension on the springs mounted on the carbs (but again don't go too tight or that front bushing will wear faster).

Here's the "More BS" link so you can look through yourself. I might have missed it.
https://drive.google.com/open?id=0B2H2NJt34OffMmE1YTU0YzctMTQyOC00MmJmLWFiZGItNTI5ZjI3N2NjZTIy

Page 22 Fig 16

 

[TR3driver]

Thanks, Karl.

 

[doc50]

*Throttle isn't bent (far as I can see)
*needles centered (good 'drop clank')
*I will look into the extra spring, (though as people have said, it would lead to increased wear on the throttle shaft in the long run...)
* Throttle shafts bushes seem to be tight, but I'll recheck those, as well as "More BS"
* I'll look at p22 fig 16.
Thank you for the ideas, folks.
Thom
1959 TR3
#TS34909L(O)

 

[doc50]

Again, thanks Terry, Joe Karl and Randall. I found the problem and it was indeed the shafts. They were worn just a bit....but just enough.

I was amazed at how one has to jigger the butterflies around when screwing them on to the new shafts. When first installed, there was a slight gap around the butterflies, so it idled at 2500 RPMs. When I redid them, I discovered that there appears to be only one way the butterflies can be mounted, even though with the beveled edge, it looks like there are two possible orientations.

Hope this may help anyone replacing throttle shafts.

Thom
1959 TR3
#TS34909L(O)