Topic: Mikuni carbs for a 460/4?

[Tel#277]

Hi all,
Just wondered if anyone has tried fitting 4 seperate 26mm Mikuni carbs (as fitted to pitbikes) to a 400/4?
I'm prepping my Tony Foale chassis'd version for CRMC in the UK next year - and my attempts to find some used 26mm CR's have proved unsuccessful.....
The bike has a 460 Yoshimura kit & cam, gas flowed head etc, and the original carbs look tiny.
Anyone got any ideas?
Thanks in advance...

[MRieck]

Why don't you run Keihin CR26's?

[Sam Green Racing]

The modern ones are not allowed in CRMC racing Mike.

Welcome to the forum Tel#277, how about a name and where you are in the UK, we also like pictures

There are quite a few people on here that might come to your rescue.

Sam.

[simon#42]

depends what class its entered in sam , they would be fine in the post classic class , not sure where else a 400 based racer would be eligible at the classic club .

[Sam Green Racing]

That's why I am a drag racer and only a spectator at real racing Simon. 

Sam.

[Sam Green Racing]

If what Simon says is correct and it probably is, you need to read this thread Tel#277.

http://forums.sohc4.net/index.php?topic=42903.0

Sam.

[Ecosse]

i have the solution to your query but refuse to divulge in the absence of pictures of tony foale bikes.




i lied. i have nothing. 

but take pity on me... i require visual moto stimuli.   

[Tel#277]

Its already had the nod to race in the 500 aircooled class group 2 period 3, gona try & show them Suzuki T500 stinkwheel things the error of their ways!
I've got to put it back to its original monoshock rear end for eligibility reasons (it was previously raced with forgotten era in the early nineties who insisted it had to be twin-shocked!)
The later type CR's are widely used in CRMC now, but 26's seem ultra rare, I'm a cnc machinist, and I could easily machine out some stock carbs to something like 24-25mm, but I quite liked the idea of the individual 26mm Mikuni smoothbores for some strange reason (maybe I just like a challenge), I could easily make my own flange adaptors to suit the stock rubbers (or can I fit larger ones from a 500/550?)
Its a bit of a departure from the big Z based Kawasaki's I've built & raced in the past (and still do) but I'm looking forward to it.
I'll try to put some decent pics on soon.
By the way Sam - I'm based in N.E. England (Durham)

[Sam Green Racing]

OK, we'll call you Terry or Tel for short. I think we have 276 Terrys on the board so you can be #277.

Tel, did you not see this thread. http://forums.sohc4.net/index.php?topic=42903.0

Sam, near Manchester untill Wednesday.

[Tel#277]

Yes I read the thread - but I simply cant find a used set of CR26's - not yet anyway, in the past (probably my Z background here) I've always preferred Mikuni's, and I figured with new VM26 smoothbore carbs being available at £20 each it may be worth a shot? - just wondered if anyone else had tried a similar mod?

[rudi]

Hello from Germany,
yes positiv I put Mikunis on my CB 400 F Projekt . Look at the Picture.
Details on request.
My next Offer : Use Kawasaki ZXR 400 Carbs !!!!!!!
Same dimension as CB 400 f Orig. and with a Alloy Adapter and Intake Rubbers ready to use !
Dont forget to construct a Air Box or use K.u. N Individual Filter othewise the CV Carbs wont work....

[Tel#277]

Thanks for that Rudi,they look like the old VM29's - do you know if they are 26mm? or what they came from?

[turboguzzi]

Have used VM26's rack on my CB500 racer with really good results, they came off a GS750 I believe

BTW, 26VM from in line fours are not smoothbore, but just because of that, have amazing response down low.

the 75-100-75 spacing was spot on for the 500, you'll have to redo the mounting plate for the spacing of your 400 I'd think  

I think you'll go through some serious hassle trying to sort an easy to synchronize  linkage with single carbs and your wrist will have to deal with four return springs but have seen it done

TG

[simon#42]

Its already had the nod to race in the 500 aircooled class group 2 period 3, gona try & show them Suzuki T500 stinkwheel things the error of their ways!
I've got to put it back to its original monoshock rear end for eligibility reasons (it was previously raced with forgotten era in the early nineties who insisted it had to be twin-shocked!)
The later type CR's are widely used in CRMC now, but 26's seem ultra rare, I'm a cnc machinist, and I could easily machine out some stock carbs to something like 24-25mm, but I quite liked the idea of the individual 26mm Mikuni smoothbores for some strange reason (maybe I just like a challenge), I could easily make my own flange adaptors to suit the stock rubbers (or can I fit larger ones from a 500/550?)
Its a bit of a departure from the big Z based Kawasaki's I've built & raced in the past (and still do) but I'm looking forward to it.
I'll try to put some decent pics on soon.
By the way Sam - I'm based in N.E. England (Durham)

yes that looks like a good new class , i watched it at brands earlier this year . all the front runners where using rd based bikes and it would be nice to see some variety .   i have never understood the classic clubs classes , group 2 i suppose is for road derived bikes ?
oh and the forgotten era club insisted it had twin shocks because it was raced in the twin shock 500 class if i remember right . if it had been a monoshock it would have been in with the tzs and rgs  and would not have been competitive at all .

[fishhead]

Alot of the "other" makes and models (Kaw 900/100 in particular ) use the 750 sandcast 1 into 4 throttle cable when going to the 4 individual carbs.

 What I have done in the past was to modify "other" application carbs to fit the application that I wanted them to fit on .

 The 1st pic is of Mikuni 38mm flatslides modified to fit the Suzuki GT 750(off a 780cc snowmobile). The carb spacing was altered to fit the intake spacing on the GT and of course, rejetted.
 The 2nd pic is a set of Mikuni 33mm flats modified for the 750 SOHC. Spacing was altered, jetting was altered,etc.

 I prefer to modify the carbs with a single throttle shaft as I hate the 4 seperate throttle cables that seam to always need to be adjusted and stretch at different rates.
 
The easiest (allthough, not very easy) would be to get a set of Mikuni 26's off a 76 KZ 900 (the 76 has the"smoothbore" style slide adjusters) and replace the carb mounting plate with a custom made one (like Rudi's set).

3rd pic:
 The 76 KZ 900 carbs have the 2 screws that hold the idle screw mount on at a 45 degree angle (they usually have the "connector Bracket" for the carbs shown-stock). These have the Smoothbore style slide adjusters.

4th pic:
The KZ 1000 / GS 750 usually have a different mount for the Idle screw bracket/Cable bracket (some KZ 1000 have the idle speed screw from the bottom). These 2 screws that hold the cable mount to the carb mounting plate are pointed down (not on a 45 degree angle, like the 76 KZ) . These carbs have the later style adjusters and are not as "easy " to work with  (when modifying) as the earlier 1976 26mm carbs are.

 

[rudi]

Here are a detailed Pictured from the Carbs
if you want more Details , please let me know, I prefere Telefon because my Computer Expieriance and my two Finger System makes it difficult...........
Dont miss the Chance...
Look at www.cb400f.de......

[bwaller]

Those are a tight squeeze rudi, would you mind showing us a pic of the opposite side too?

[rudi]

Ok i will do my very best.............
Some more pictures ........

[rudi]

The PC kills me....................

[rudi]

aaargh...............

[Tel#277]

Thanks for all the help - looking at a couple of the links Rudi sent maybe I should look at Amal concentrics as an option....
If I can figure out how to post pics I'll put some on!

[Tel#277]

Here's some of the Foale in its previous (twin shock) guise, as well as being monoshocked as per original, I will be switching to bigger discs & Brembo or Lockheed brakes, and of course a fairing (probably a Davies Motorsport K4 item)
I'm undecided about a colourscheme, my thinking is the red with silver fairing thing is a little before its time...

http://s669.photobucket.com/albums/vv59/Telsport-racing/

[turboguzzi]

very nice tool! pretty rare too,

from my experience, you should reel in the T500's but dont expect to get too near to the RD 350's unless your cut off date is 72' (so those are only R5's with 5 speed boxes).

definetely go for bigger discs.

cool stuff rudy,

TG   

[754]

I think i have a set here somewhere off an 80 GS750., look like the ones in the pic for the 400.. anyone know if they are 26mm ?

[rudi]

Yes if they are from a Suzuki GS 750 they are 26mm Venturi . We use them to tune up a CB 400 f with 500ccm³ Powroll Big Bore Kit. It works but not without changing the Internal Parts like Needle / Jets etc.
Check in the Picture Galary cb400f.de about "Karsten Laue " and you can see the Result.....

[fishhead]

The 26's can be told apart from the 28's by the thickness of where they mount to the carb holders (engine side).
 Right side top - 26mm
 Right side center - 28mm
 The 28's are noticably thinner than the 26's

Rudi's are 29mm smoothbores. They can be told apart from the 26-28's by the extra castings in the intake side bell (none of these shown in my pic are 29's- no extra castings in the intake side bell)

[turboguzzi]

Yes if they are from a Suzuki GS 750 they are 26mm Venturi . We use them to tune up a CB 400 f with 500ccm³ Powroll Big Bore Kit. It works but not without changing the Internal Parts like Needle / Jets etc.
Check in the Picture Galary cb400f.de about "Karsten Laue " and you can see the Result.....

do you have any pics info on those powroll pistons?

tnxs

TG

[Tel#277]

I assume the carb rubbers aint the original size with the Z900 carbs? - do the CB550 ones fit?

[turboguzzi]

I assume the carb rubbers aint the original size with the Z900 carbs? - do the CB550 ones fit?

I've used the stock 500/550 with the 26VM's, they work fine

[bwaller]

They work fine with the 28's too, (same carb inlet OD) although not if they're old and hard.

[rudi]

Hello from Germany.......
Answers to all your Questions : Yes I use different Intake Rubbers on the Cb 400 F Cyl. Head together with a Alloy Plate which I bolt on to the Head by using the Orig CB 400 F Thread Positions. I use Kawasaki Z 1000 A1/A2 Intake Rubbers with mold in Tubes for the connection of the Balancing Hoses.
The Carbs are Mikuni VM 29SS Rac. Carbs.
Photos from the 500ccm³ Powroll Pistons are not availabel. They are also sold out since a Long Time .
But dont worry , look over the Fence............
Have a look at at www.ooracing.com . They offer Pistons with 13 mm Gudgeon Pin and up to 60 mm .........The only wrong Thing is : They are 3,25 mm too short , look at the attached Photo.
The other Picture shows my 450 ccm³ Yoshimura Piston Kit which I upgradet with a low fricticion coating on the piston skirts .

[rudi]

Pictures...

[rudi]

pictures...

[turboguzzi]

Hello from Germany.......
Answers to all your Questions : Yes I use different Intake Rubbers on the Cb 400 F Cyl. Head together with a Alloy Plate which I bolt on to the Head by using the Orig CB 400 F Thread Positions. I use Kawasaki Z 1000 A1/A2 Intake Rubbers with mold in Tubes for the connection of the Balancing Hoses.
The Carbs are Mikuni VM 29SS Rac. Carbs.
Photos from the 500ccm³ Powroll Pistons are not availabel. They are also sold out since a Long Time .
But dont worry , look over the Fence............
Have a look at at www.ooracing.com . They offer Pistons with 13 mm Gudgeon Pin and up to 60 mm .........The only wrong Thing is : They are 3,25 mm too short , look at the attached Photo.
The other Picture shows my 450 ccm³ Yoshimura Piston Kit which I upgradet with a low fricticion coating on the piston skirts .

the powroll ones look good but are they 14 or 15 mm pin?

the ooracing ones looks familiar from so many other asian monkey-bike tuning shops. If you look hard enough youll find also 14 & 15 mm pins pistons. BUT, they will all have very low compression height. I accepted the challenge and shortened my block big time, had to find also some creative solutions to keep the cam chain tension (transplant of a CBR600 tensioner)

[Tel#277]

I've got the new "manifold" manufactured, and fitted Suzuki GS1000 vm28 carbs to the 460 motor,(though I'll need to do something with the cable mount as its too close to the Foale chassis rail).
As the chassis is that tight for size, removing the carbs for jetting changes is going to involve dropping the motor down/forward in the chassis, so any advice on jetting for them would be REALLY appreciated!

[specweld]

test run .
Tel contact Dave Roberts, Hartlepool.
dplatforma@aol.com
re honda

[specweld]

Hi tel,never done this before, hence the test run.
I have a 400/4 (bored to 500)
lightened ,balanced,polished crank
Robson rods (yes Robson not carillo)
web cam
gas flowed head
1mm oversize valves (inlet & exhaust)
26mm CR carbs
Dyna 2000 ign.
close ratio gearbox
TZ front end, AP brakes
TZ rear end, AP brakes
 etc. etc.
I have been playing about for years with cb400's. and if I can be of any help just get in touch, I'm only down the road from you in hartlepool.

I know 3 lads who run 500 hondas in CRMRC and they all use modern CR carbs.
Am not up to sending pics yet , but if you go to TTR400 site , click on SOME HOT 400'S , the first 3 pics are my honda (the yellow one),it's well worth browsing the rest of the site (loads of goodies, some in my bike) and kevin (who runs the site) is very knowledgable and helpful.

Dave

[Tim2005]

Tis good to see another 400 fan. Which Web Cam grind do you use & what's your opinion of it?

[specweld]

this particular engine is still running in so not sure how it will compare to others in the past. The cam is the softest of the 3 grinds,I think it was sent by mistake but the guy who did all the porting and valvework did some calculations and suggested it would work out better than the full race cam , he said he could get more or less the same flow figures but keep the power output further down the rev range.
(sounds good to me)

He has flowed several cb 500 heads with full race cams (inc. Col Stockdales engine) . we compared the results and the flow rates are almost identical .

Incidentally, the cheapest and most effective way to improve the carburation £ for £ is to bore them out and rejet them, plus you get the benefit of everything fits as it should. I have a set already set up and jetted,
you can try them on your bike if you want, an if happy you can just copy all the mods on to a standard set.