how to make a carb setup throttle less "twitchy"

This is a dumb question, but I can't seem to get it right. On the GT6 I have an SU HS conversion, and cable throttle conversion (replacing the old rod and lever setup). The setup was "improv'd" using a Tercel cable and a bracket from something I don't recall offhand (I think maybe some other old british car). Basically there is alot of initial resistance and then very little resistance. Basically I have to slip the clutch a bit when in traffic for fear of rear ending cars in front of me, lol....

Ever since I've had it set up the throttle has been super-twitchy from idle. I've adjusted the angle of the pull, the cable attachment point on the pedal level, and a few other things but nothing has really helped. The next step? I guess something with the return springs on the carbs themselves? Can these be adjusted or replaced with a weaker spring.

anyhow, any thoughts or advice is welcome. Maybe another lever setup? IDK. Brain freeze. It's been so easy working on the e30 that I think I've forgotten how to work on the LBC.....

Here are some pics

btw, the red cable in the pics is old. It currently has a cable that is a more appropriate length :)

lol....it's not that. It's the fact that once you overcome the initial tiny bit of travel on the pedal, it's at like WOT and super-light like a hair trigger......

I still fail to see the problem.

But seriously, I would think that replacing the return spring on the throttle with a heavier spring would be more helpful. If the throttle has to overcome more resistance to open it will be more docile.

Other than that I don't really have too much experience with carbs.

haha....yeah, that' s my problem too. This is the only car I've had with carbs, and it went from the rod-linkage mush Strombergs to the SU setup that's totally opposite. Carbs are not my strong point, other than basic tuning and setup.

If you look at factory setups on more modern stuff, you will often find a thingy....doodad...grooved pulley 1/4 kinda thing- I'm sure there is a word for it... anyway, it will often be set up with the initial pull being longer, and the pulley tapers down to a smaller length, giving you greater mechanical advantage and finer control at smaller throttle openings, then getting faster the more the throttle opens. I shall search for a picture to ruthlessly hotlink.

Imagine this, but not round. Or round, I guess, but with the pivot hole off center.

hmm....that makes sense. I wonder how I could set it up on this car. I'll have to look more closely at some cars at the JY, since all my cars here except the e30 are drive by wire

I built one like the above for my dual DCOE throttle bodies using a piece of aluminum, a hole saw and a file.

I cut out a round disc with the hole saw, spun it in my drill press using a bolt and filed a groove in the edge with a file and some sand paper.

You can use a round cablestay to hold the cable in place on the disc with a drilled hole in the outer edge. Elongate the center hole to fit the shaft.

irish44j wrote: haha....yeah, that' s my problem too. This is the only car I've had with carbs, and it went from the rod-linkage mush Strombergs to the SU setup that's totally opposite. Carbs are not my strong point, other than basic tuning and setup.

I haven't even gotten to drive my car yet so I can't sing it's praises, but my l24 has SU's with a rod linkage, seems like maybe will fit with very minor modifcations?
Always felt like a rod linkage would be a lot more direct than a cable from another car, but maybe not. Have not done testing on the theory at all lol

make that alot of modification considering what side of the engine the intake is on. lol
didn't think that one through.
and anyway, why would you need anything other than WOT?

I dicked around with levers and bellcranks for a while w/ the DCOE on my Sprite. Ultimately it was an exercise in competing monkey-motions, and I decided that linear things I can understand. So I made the linkage in the image below out of some aluminum, a bit of stainless rod and a couple toothed-belt pulleys and a bit of belt. The splice on the belt is on the slack side - I thought I'd buy one the right length, but it's been years and years and it works fine.

A bell crank would work better. What I see is the length of the levers on the linkage shafts are to short which means your throttle pedal has to overcome that lack of leverage on the shafts.

Streetwiseguy wrote: If you look at factory setups on more modern stuff, you will often find a thingy....doodad...grooved pulley 1/4 kinda thing- I'm sure there is a word for it... anyway, it will often be set up with the initial pull being longer, and the pulley tapers down to a smaller length, giving you greater mechanical advantage and finer control at smaller throttle openings, then getting faster the more the throttle opens. I shall search for a picture to ruthlessly hotlink.

Roller cam linkage?

Look down the throttle barrel and make sure that the butterfly is not binding in the barrel when off throttle. You may need to adjust your throttle stop...then the idle mixture.