RGS Mikuni conversion

ksoholm

ksoholm

Senior member
Location
Bellingham, WA, USA
Lads,

I'm embarking on a Mikuni conversion on my restored RGS. The bike has Witt DMC2 and Jota cans. I've read lots here on the how-tos - Redax's angled intakes, etc. - and intend to use the stock airbox. My only question is which dual-pull throttle have you found to work well with the stock switch assembly?

Any other fine words of wisdom?

I expect the change in running refinement to be substantial, as it was on my Moto Guzzi Sport 1100 when I installed Mikuni flatslides on that last year - way better than the PHM40s.

Thanks-

Kristian
 
If you're talking RS36 then -
https://www.motionpro.com/product/01-0316  You can machine the ND switchblock to accommodate the screwclamp end of the twistgrip and everything will then fit neatly on the bar.

Angled intakes means lining up the inlet rubbers with the airbox will be a challenge. Shortened straight inlet stubs work best for that, but you're at the limit for permitted carb operating angle.

Although a twin-pull is recommended by Mikuni, apparently you can get away with a single pull on a Laverda triple.

The choke operating rod mechanism can be extended by cable to the bars, but in my experience the brass choke plungers will then wear against their vibrating steel operating tangs resulting in no choke operation after a while. This is because the detent ball bearings that operate against the rod need to be removed to get the cable operation to work satisfactorily.

 
I use a cable operated choke on my RS36 carbs and have good operation even with the detent ball bearings in place.
 
Using a twistgrip from a '80s model Suzuki with CV carbs allows fitment of dual cables, identical to original but with 2 cable openings.

I've never bothered with the dual cables, even removed one of the 2 return springs to makes things lighter on the wrist.  Stock choke lever works fine with the cable choke conversion.

piet
 
sfcpiet said:
Using a twistgrip from a '80s model Suzuki with CV carbs allows fitment of dual cables, identical to original but with 2 cable openings.
Click to expand...

Bear in mind, you have to ensure that there is no free play in either cable when using dual cables.
Otherwise you will come into a turn on open throttle, and then if you need to back off, the drop off will be too great. That's exactly what I was adjusting here, for that very reason:
IMG_2730.jpg
 
How so, Chris? Can you elaborate.
Isn?t it standard practice to always have some freeplay in cables to allow for maneuvering or it?ll pick up throttle. I have always installed with a bit of play twin or single cable, never encountered your problem.
 
Tippie said:
How so, Chris? Can you elaborate.
Isn?t it standard practice to always have some freeplay in cables to allow for maneuvering or it?ll pick up throttle. I have always installed with a bit of play twin or single cable, never encountered your problem.
Click to expand...

FI Grant.

The top cable is to open the slides, butterfly or whatever you have. The bottom is to assist the slides, or butterflies to close. If, particularly the return cable is too loose, the rpm drop, as you roll off the throttle, can be too great. Think of it as a tug o war rope joined in the centre by a large loop. The greater the loop, the more play it has when the tension is removed.

The single cable, holds the slide up, no matter where the slide is due to spring tension, except if the slide fully is closed. Flat slides use the return cable to assist return, as they have a habit of sucking still, if the spring tension is too low, or god forbid, the spring breaks.

I?m not suggesting there be no slack on the throttle cable when fully closed.
 
My point was that perhaps FI  is more critical of cable slop than slide carbs.
 
Grant said:
My point was that perhaps FI  is more critical of cable slop than slide carbs.
Click to expand...

Maybe so, but either way twin cable position is critical, even with carbs.

I've seen a bank of 3 flat slide carbs not open fully because of the twin cable position
being set incorrectly, a trap for (not only) young players.  :-X
 
I don't follow your reasoning Chris. The throttle opening cable is always under tension because of the return springs (except when slides are closed). If there's slack in the return cable, how can it pull the throttle closed too much?

The return cable actually does bugger-all. It's normally under zero tension at all times. It's only there as a fail-safe. The only time it ever comes into play is if the system sticks enough that the spring(s) won't close the throttle. You could delete the return cable and not notice any difference - as Rob mentioned earlier.
 
Dellortoman said:
I don't follow your reasoning Chris. The throttle opening cable is always under tension because of the return springs (except when slides are closed). If there's slack in the return cable, how can it pull the throttle closed too much?
Click to expand...

Good point, and well made. Maybe this is a failing of the FI system set-up (dunno)

I put up with this while overseas, and with the off throttle back-pressure of the 1400 it was almost dangerous. If going into a bend too hot, rolling the throttle off just backed the rpm off so much it near locked the back wheel, unsettling the bike. It was like there was a gap between on and off the throttle.

When I picked up the bike from the shippers last week, I went to Eastern Creek to see the Laverda team, and adjusted the return cable so there was no slack. Wish I had thought of this while I was away.

The ride back home was a pleasure, rolling off the throttle was just that .... no major drop in revs, just a smooth roll off. 

The flat slides on my GSXR, with one cable means I need a very heavy return spring to shut the slides, otherwise the vacuum would momentarily hold the slides open, and therefore the revs.
I have recently bought an R1 throttle to allow for two cables, as intended.

 
when I was racing my Montjuic (1979/80) which had stock Delortto's and single pull cable, it was easily possible to get into trouble (rear wheel patter) entering corners and snap shutting the throttle together with hard downshifting, something I learned to be a bit more genteel with over time, in fact the rear brake only came into its own mid corner and (sometimes) on exiting/charging away.
CLEM
 
When Mark, Reds mate first fitted the Miks on my 3C the return spring was that strong I couldn't easily blip the throttle on down changes. Mark then backed the return sping down one setting, it's done by removing a bolt on the throttle shaft and allowing some tension off and replacing the bolt that holds spring tension. That made a huge difference to the tension returning the throttle to idle. That's on a bank of 3, no idea if that's applicable to single carbs. Ask Mark. I have pull and push cables and zero hanging idle issues and a nice light action.
 
You must log in or register to reply here.
Back
Top