The Official Mikuni Flatslide Carb Thread

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

I made a statement error which should of said the TMs should flow slightly more than the RSs due to the bell mouth opening radious allowing smoother air flow entery to the venturis,it dosen't mean the RS are bad but the surg factor you're looking for may not happen till you get in the 36 to 38 mm sizes,depentant of engine displacement.You still have a far superior carburetor then any OEM or any round slide out on the market. When jetted for proper air fuel ratio,you'll difinitely notice the smoother power delivery and torque boost and the wow factor....................Jack

Cooltouch

I have a set of 36 roundslides I bought for my cafe project, but all this talk about the advantages of the flatslides has got me reconsidering. Prolly be a while before I'll have the funds to buy a set of the flatsides, though.

Still, I'm wondering what carb size and what sort of settings I should expect for my application. The bike will have the 763cc big bore kit (with 10.25:1 cr), a Webcam 59 grind cam, mild port-n-polish work to the head (removed the rough machining marks and smoothed things out), and 2-into-2 exhaust, probably with shorty reverse-cone megaphone silencers. Maybe Norton-style peashooters (I have a spare set of genuine Norton ones).

I suspect that 34 flatslides will be adequate, but I don't really know. And I haven't a clue, really as to what sort of jet/needle/slide combination I'll need. Those of you who have a feel for this, care to offer an opinion -- or point me to a source on the web where I might be able to glean a workable combination?

Best,

Michael

TheDude

has anyone used kiehin flat slides (like 34mm pj carbs off a Yamaha Banshee)?

xsjohn

How much gas can go into these things without plug problems......?

xsjohn

81XSChopper

Looks like this is going to be quite a deal for a flatside carb -- if you are lucky enough to find another matching one...

cgi.ebay.com/ebaymotor...dZViewItem

greg

TheDude

at the risk of creating competition, there's a ton of flat slide carbs on ebay right now. Thus my inquiry about the kiehins. There's a bunch of Mikunis as well. I just use the key word "flat slide" or "34mm" in a search of all ebay motors. Most of the hits are snowmobile carbs, but I can't imagine there's any difference aside from maybe an oil injector barb (which I think might work for vacuum petcocks/carb syncing)

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

If you added up the cost of brass to convert a 2 cycle carb over,you'd be better off just purchasing a 4 cycle carburetor..................Jack

daddyk · New Member Joined: Jul 18, 2005 Posts: 9

Back with a RS jetting update. Mikuni seemed to know what they were doing with the jetting. The P-8 NJ turned it into a burbbling mess, to rich. It came to me with a 9DZH05 needle which is the richest listed. Tried all the clip positions with the P-8,none were as good as the P-4 NJ one step rich on the clip. I am at 135 MJ now gives a better plug color and even more topend. It has no trouble hitting redline in top gear in a hurry. Only room for a quick blast on the road.Shhh don't tell any one. That's with stock gearing and it's pretty freaking fast. I am running a 59 web cam and Mac two into one exhaust with the stock asmatic baffel out and replaced with a White Bros. 10" baffel. I can only say I'm very happy with the way it's turned out. Starts easier,idles better,pulls better all through the rev range. Oh and on the pumper aspect of the carbs you can feel it but only if you really jerk the throttle open especially in the lower gears it really shoots out. If you're rolling the throttle on normally I can't really notice anything.

krauser4valve · New Member Joined: May 28, 2008 Posts: 3

I found this thread from a google search, I'm having a hard time getting the pilot jetting correct on my bike. It's a 77 BMW R100rs w/ Krauser heads, Supertrapp CC exhaust and TM36-2 carbs. I currently have #30 pilot jets fitted and it's still running too rich, blackening the plugs and stinking the neighborhood up. Any suggestions that can get this thing running right would be appreciated and rewarded with some sort of beverage.

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

Not into motorcycles anymore but I might be able to assist you in jetting the Flatslides. Does the Kruaser head have the spark plug centrally located between the valves and give me your exsisting jet combination your running now.......................Jack

krauser4valve · New Member Joined: May 28, 2008 Posts: 3

Yes, one 10mm plug in the center. This link is pretty much what my bike looks like www.geocities.com/knut...080767.htm The jets are:

Main: 4/042 180
Pilot: VM22/210 30
Needle Jet: 389 Q-6
Needle: 6FJ40
Throttle Valve: 832-43002A 4.0

Thanks

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

Very "SWEET INDEED" Wink

I have a 76 R90/S that's been intensely modified,dual plugged,38mm flatslides,336 cam,ported head,punched out to 1000CCs and Super Trapps,hp#s, don't really care but you best be holding on to grips when you nail the throttle Laughing

With the plug being centralized, the flame front is much shorter and combustion efficiency is incresed,therefore fuel demands need to be reduced or you'll be faced with overly rich condition,as you,re experiencing now. My suggestions for the pilot is drop down to 20 but have on hand a 17.5 and 22.5 they're inexpensive anyway. On your initial take off,you want no hesitation and if by any chance when you come to a stop and the motor coughs and dies,you need to step up to the next highest pilot jet. The main jet seems to be on the lean side for the application but once you get the P/J sorted out,place in first gear and NAIL THE THROTTLE WIDE OPEN and hang on Laughing

If the motor falls flat on its face,your to lean on the main jetting, step the jets up till the motor pulls cleanly from a dead stop,once you get the main jet sorted out you can proceed to tuning the jet needle and needle jets but always remember if you change the needle jet to leaner setting,you'll most likely need to fatten up the main one step,just use the spark plug coloration as your tuning tool...........Jack

krauser4valve · New Member Joined: May 28, 2008 Posts: 3

I just came back from the local Yamaha dealer who only had a one #20 and 2 #15's, so I sprung for the #15's ( I hadn't seen your message yet). Bad move, won't even idle unless the enricheners are on. I'm going to just order a few pairs to play with like you suggested. What mains are you running?

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