Mikuni

Paul Marx

Paul Marx

Hero member
Location
France
I'm pondering rebuilding my long suffering SF2 before it blows up and before there's nobody around anymore for some of the specialised work.
Whilst I'm at it, why not upgrade the carbs.
Before I splash out, are these what everybody's using?
www.kedo.com

TM36 Flat Slide Carburettor, WITHOUT rejetting kit, not street legal, hose connection diameters: fuel/low pressure 8/6mm

Application: SR500, TT500, XT500 MIKUNI TM Flat Slide Carburettor Easy way to more power without engine modifications; power increase depends on intake and exhaust, an increase of 3 hp and more is possible over the whole rev range Equipment: Carburettor with accelerator pump, throttle...
www.kedo.com www.kedo.com
Paul
 
It's an IN joke, I got a laugh. Paul has been a 100% leave those points alone supporter for so long here, it's a bit shocking, a little pun, to hear him propose a post stone age mod to a Laverda Twin. Maybe he should consider a Magneto conversion instead.
 
Ok, Well that makes more sense... ;)
Personally i think different horses for different courses.
I have a couple of BSA B50 MX's that still run points! tried Boyers, (best in the bin!)
Least with points on a big ish single the Plug fires how ever slow the engine spins.. well that's the way i look at it.
Ran my T120 RV with points for about 35 years, till a points foot randomly broke so swapped to TRISPARK.
My old T120 beach race bike is still on Magneto! which is always fun in the Paddock.... if not my bike... then others! as people think you know stuff.
other than that its a Black box for me too
 
I have 39mm Keihin FCR on my non standard SF. A mate fitted 35mm to his stock SF3 and was totally happy. A challenge is the height under the frame so they have to fit on short manifolds, not really a problem, and before I put it on the track and extended the manifold length I had it on short manifolds and the standard rubbers connected between the carbs and the stock airbox. Another challenge, for me anyway, was fabricating a connector between the two so that I could use a single opening cable (I also fit a closing cable). I robbed the synchronising parts from a useless set of carbs off some Jap bike from the wreckers, I didn't like the tiny amount of possible adjustment in the standard synch system within each carb top. I also had to very carefully bracket them together so that they are aligned otherwise they can open at different rates. None of this was particularly hard to get done, and they work brilliantly and very easy to jet. The other thing we have done is leave the acc pumps disconnected for the throttle and just use them to squirt once for cold starts, Quentin modified a choke lever to do this, I just use the little lever on the RH carb as the pump system is linked via the float bowls, dead easy. There is no slide rattle, or I may be deaf.
 
To give Paul an honest answer:

Hi Paul, on the 3 cylinder Laverdas, most use the RS-Series Mikunis. They look very similar and to be honest - I have no real clue what the difference is... You could ask Stephen Topham, a brittish guy living in Germany since decades, who is the importer for Mikuni in Germany. Very nice guy, helped me on my Keihin-Conversion even and he offers kits for 3-cylinders and also for Laverda 500s already (in that case TM36-150). He might help you on the size of the carbs, the differences etc. and maybe even can offer you a complete set of carbs. The price on the page that you linked above is tempting though... However, Stephen can build you a set, spaced to fit the 750's if you send him the measurements (if he doesn't have them).


Single/separated carbs is no good for this application I would say as you have two cables each carb already, one that opens and one that closes the slider. If you use 2 single carbs, you end up with 4 cables... So - a properly spaced and adjusted set makes sense, which he offers for something like 695€ for the 500's. A one-off would not be much more expensive, I am sure, as he spaces them individually anyway...

I assume though, due to the higher displacement, he will recommend you a TM38 or even TM40 on the 750's. In the Laverda-World, this sounds big but keep in mind: most Guzzi owners convert their 750's and 850's to 40mm carbs, too, same displacement, same number of valves etc. ... TMR's are also an option, but a bit more expensive. They have a very different design with steel roller bearings for the sliders. Much easier and better controlled operation. They are the top class of the Mikuni range.

I have 41mm carbs (Keihin FCR) on the 1200 Laverda (well - 1116 or so) and they work well. You'll need to adopt your right hand though to the carbs, as they are much more "snapy", but also can cause a stubborn driving behaviour if you pull them open to quickly...

Good luck and let us know how you like them!
 
Laverdalothar said:
To give Paul an honest answer:

Hi Paul, on the 3 cylinder Laverdas, most use the RS-Series Mikunis. They look very similar and to be honest - I have no real clue what the difference is... You could ask Stephen Topham, a brittish guy living in Germany since decades, who is the importer for Mikuni in Germany. Very nice guy, helped me on my Keihin-Conversion even and he offers kits for 3-cylinders and also for Laverda 500s already (in that case TM36-150). He might help you on the size of the carbs, the differences etc. and maybe even can offer you a complete set of carbs. The price on the page that you linked above is tempting though... However, Stephen can build you a set, spaced to fit the 750's if you send him the measurements (if he doesn't have them).


Single/separated carbs is no good for this application I would say as you have two cables each carb already, one that opens and one that closes the slider. If you use 2 single carbs, you end up with 4 cables... So - a properly spaced and adjusted set makes sense, which he offers for something like 695€ for the 500's. A one-off would not be much more expensive, I am sure, as he spaces them individually anyway...

I assume though, due to the higher displacement, he will recommend you a TM38 or even TM40 on the 750's. In the Laverda-World, this sounds big but keep in mind: most Guzzi owners convert their 750's and 850's to 40mm carbs, too, same displacement, same number of valves etc. ... TMR's are also an option, but a bit more expensive. They have a very different design with steel roller bearings for the sliders. Much easier and better controlled operation. They are the top class of the Mikuni range.

I have 41mm carbs (Keihin FCR) on the 1200 Laverda (well - 1116 or so) and they work well. You'll need to adopt your right hand though to the carbs, as they are much more "snapy", but also can cause a stubborn driving behaviour if you pull them open to quickly...

Good luck and let us know how you like them!
Click to expand...
Thanks Lothar, but it's a rather long term project, first do the crank, valves, guides and a rebore. But the again, who knows.

The bike has been running rich on the left hand side for forty years even though I've changed the carbs for new 10 years back.
Maybe I should change the condensers? They've been there since 1973.

Paul
 
Quaint term "Condensor" from the days of Leyden Jars, that electricity "condenses" in the jar ( was an actual glass jar, with metal foil on the outside and inside ( modern capacitors have this "outside foil" ) annunciated on the pig tail type, as a tangental black line on one end. The actual value of this condensor is of some argument, in kettering systems.

The correct value ( perhaps 0,22uF ranging down to 0,1uF ) primary task is spark quench, secondary is to "ring" the primary winding for sustained multiple spark energies. Only real way to optimise this ringing is by observance and experimentation, nothing new to Laverda folk..

Mikuni Condensor, how novel, ringing endorsement if ever to be so, to stay within a topic...or no, a smile here. j.
 
Paul Marx said:
The bike has been running rich on the left hand side for forty years even though I've changed the carbs for new 10 years back.
Maybe I should change the condensers? They've been there since 1973.

Paul
Click to expand...
What are the signs of it, please? black, maybe even wet spark-plug? could be indeed pointing to a spark problem rather than a carb problem maybe...?
 
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