Lighter Mikuni RS Flatslide Throttle Return Spring?

[MOTOMORON1100E]

I installed a set of RS34-D21K Mikuni flat slides on my recently completed '82 1100E , with a Domino push/pull throttle and new custom Venhill cables..  K&N offset oval individual filters, Vance & Hines 4-1 exhaust. Valve lash set, carbs balanced with gauges. It runs GREAT.

But the throttle return spring is extremely heavy. As in numb hand after a half our. I tried one of those clip on the grip plastic palm things, and it slowly works it's way around the grip. 

I found a lighter spring for the big Mikuni HS/HSR 40+ mm Harley carbs from Mikuni OZ which is dimensionally identical to the stock spring, but wound from 1.55mm vs 1.77mm wire. It's a little lighter, but still much heavier than I'd prefer on an all day motorbike. 
I tried moving the hook on the spring to the other post, which results in a dead spot before the spring is engaged. 

Potential solutions include: 

Anneal the hook on the spring and form it so it has about 20 degrees of pre-load when engaged on the alternate post. 
Measure and buy a spring from McMaster-Carr's springs made to your specifications service. 

Has anyone else solved this?

[coombehouse]

I fitted a set of 38mm flatslides with the spring on the alternative post & it all works fine. Still not exactly light but better. Have you considered that the carbs may just have the wrong spring fitted. 

[Gixer1460]

With a push / pull throttle set up I'd loose the stock spring completely or add an entirely remote spring - like a lighter coil spring - if you require 'auto' close. Also bare in mind a 'Quick Action' throttle will make any throttle action much heavier - great with CV's but murder for slide carbs!

[Mike711]

I had a Q/A fitted with 34s & lasted 1/2 hour before giving up & going back to a std set up. It's now prefectly comfortable & I can live with slightly longer throttle action.

[Dezza]

I have RS carbs on a bike I recently rode for the first time. It has a Motion Pro twistgrip and cables. I have not ridden a bike with RSs before. The action is heavier than CVs but not too bad. It definitely takes some getting used to though, especially getting the free-play right and the different behaviour overall to cv carbs. Blipping for downchanges is different as is throttle response in higher gears at low revs. You have to be smooth with the throttle. When the accelerator pumps kick-in on acceleration it's also completely unlike anything CV. I just think they need some getting used to and minor fettling. I did have to faff a bit getting the cable routing correct to get the lightest throttle action possible so maybe there is scope here for improvement re: OP.

[Mike711]

To revive an old thread, I spoke to Allens Performance who import Mikuni and they said there are 2 return springs on RS carbs and I could remove one or there are also different locating pegs for the springs that will lead to a lighter action. I haven't tried either mod as my carbs are still with Allens having a 30yr service but I will be experimenting when they come back.

[Mike711]

https://www.allensperformance.co.uk/carb-kit/alternative-throttle-return-spring-chart/

[Dezza]

1 hour ago, Mike711 said:

https://www.allensperformance.co.uk/carb-kit/alternative-throttle-return-spring-chart/

Which one's the spring supplied as stock?

[Mike711]

1 hour ago, Dezza said:

Which one's the spring supplied as stock?

Sorry I don't know, I'll be talking to Allens soon about mine & will ask them.

[Gixer1460]

6 hours ago, Mike711 said:

https://www.allensperformance.co.uk/carb-kit/alternative-throttle-return-spring-chart/

This is for VM type carbs and the return spring is internal over the slide and under the cap ! No RS carb has springs nearly 4 or 4+" long !

Looking at the RS36 data sheet - https://www.allensperformance.co.uk/carb-kit/rs36-d3-k-data-set/ - there are no alternative closing springs! Just different posts that spring mounts on.

[dago]

On 3/21/2023 at 11:48 AM, Mike711 said:

To revive an old thread, I spoke to Allens Performance who import Mikuni and they said there are 2 return springs on RS carbs and I could remove one or there are also different locating pegs for the springs that will lead to a lighter action. I haven't tried either mod as my carbs are still with Allens having a 30yr service but I will be experimenting when they come back.

I've just tried this at the weekend, I unhooked the spring nearest the outside of the carbs and put the middle spring on the middle post, it's a lot lighter and no sticking so far