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Hi,
I'm in the pretty unique position of wanting less butterfly opening per unit pedal travel, i.e. I need to bring the power in more slowly to stop the wheels spinning. Has anyone modified their linkages or throttle levers/pedals to do this?
Cheers

Never tried it, I’d suspect you’d lose being able to achieve Wide Open Throttle though.
The only real way to reduce opening speed is to alter the ratio at one end or the other and as it’s a linear system this will affect the total movement

The SU HIFs have a large cam on the carb body that rotates the butterfly shaft...can you get different sizes/diameters of these?

Thicker oil in the dashpot ???

That's a good idea Catmint! Not many people understand that little well thought out 'not-quite-a-one-way' damper valve system at the end of the rod in the cap.

I got this throttle cam in one of my batches of H4 parts. I was planning on giving it a shot as I thought the twin 1.5” carbs might be a little touchy from idle

It uses the larger throttle spindle diameter but there’s a few ways to adapt it to the smaller HS2 spindle

And another idea is a linkage like you’d find on a Weber/Dellorto. It gives a nice feel at low throttle openings Or like the minisport/Taurus style for hs2 if you can get the angles right for a progressive pedal

I think that a LARGE diameter throttle quadrant that Tim shows will give a GREATER throttle response per inch of pedal travel. When YJM wants a LESSER, more gentle throttle response.

Thinking of the standard carb/cable connection, maybe you ought to SHORTEN the length of the lever part that connects the cable to the central axis spindle. Easy to work out mathematically. But that's a job for someone clever

Or just use a bit of judicious foot-work when accelerating.............

timmy201 wrote: ↑Tue Jul 02, 2024 10:58 pm I got this throttle cam in one of my batches of H4 parts. I was planning on giving it a shot as I thought the twin 1.5” carbs might be a little touchy from idle

It uses the larger throttle spindle diameter but there’s a few ways to adapt it to the smaller HS2 spindle
IMG_0827.jpeg

The beauty of such a cam/quadrant is that you get constant travel over angle, opposed to a simple lever where travel relativ to angle results in less and less opening angle over cable travel. (either positive or negative progression, depending where you have the lever set to).

YMJ wrote: ↑Tue Jul 02, 2024 4:13 pm Hi,
I'm in the pretty unique position of wanting less butterfly opening per unit pedal travel, i.e. I need to bring the power in more slowly to stop the wheels spinning. Has anyone modified their linkages or throttle levers/pedals to do this?
Cheers

Back to "slow action throttle": ever thought to use a cable ratio thingimomabob? Like in below photo. Of course you would need to invert it, i.e. "cable in" becomes "cable out" and vice versa.

Source:
https://www.scooter-center.com/en/throt ... -cmdmn0010

SPQR did a red plastic throttle quadrant for the HS2 carb. Supposed to make for smoother action. Never used one but have a carb with one in my stash.

As seen on Marks brochure pages.
https://mk1-performance-conversions.co. ... spqr-2.pdf
Item No. 23

Hi Peter, I think maybe you got it the wrong way around...
The LARGER the throttle quadrant (or LONGER lever) the less butterfly movement you get per pedal movement..

There have been SUs with 'eccentric' quadrants, to give non-linear movement -a 'softer' start..

I seem to remember cars like the Triumph Dolomite had a multiple-lever set-up to give a non-linear movement (lots of pivots to wear..!)

Hey, Andy....... You are RIGHT! I went into my workshop and tried it with a bits of meccano as a lever and cable and a pulley!

Good job I kept a lot of my old Meccano set!

Regards from Abingdon

Use a snail cam on the carb spindle. Been pretty common on large capacity powerful engines for ever....
Lots of pedal progression to lift off idle, but going from 3/4 to WoT only needs to bury the pedal the final 1/8 inch into the carpet pile.

I have an SPQR throttle quadrant on the twin HS2s on the Hornetto - transformed it.

Splinter, when it was still a boring 850 Countryman, had an SPQR quadrant on its single HS2.
Mark Burnett inherited that when he bought the car, so it may be in the SU museum now.

We used to beef up the throttle springs as well