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Revision as of 22:00, 26 August 2016
Motorcycle carbs, bike carbies. Flat-slide, constant vacuum or variable venturi carburetors.
Contents |
Overview
TUNING is critical. Bike carbs as-is run poorly on automotive engines. But with the right jet or needle selection they can run very well.
Keihin Flat CR (FCR)
bike carbs on A12Y engine
Matsuoka MSR carbs
adapt carbs from your favorite motorcycle
Suzuki GSX-R (aka GSXR)
Yamaha YZF-R1 (aka R1) carbs are a fad in USA as of 2012.
ヤマハ
Adapter Kits
Fumiya Kit
Datsun 1200 enthusiasts Fumiya sells these
Keihin FCR
rallytwit made 73.22 RWHP on his A-series.
39mm FCR carbs with a near standard GX motor; ported head, headers 2 inch exhaust and 14lb flywheel. As far as reliable FCR carbs are stone axe reliable. For street (or racing) use you would have to do some tuning but it's not a big deal. I only needed an hour of dyno time to get the car 95% dialed. My only problems were because the carbs were on 175HP A-series powered sports racer so the jets were way off what my motor needed............lots of guys use these on street bikes and they are standard equipment on MX bikes. 32MM would likely be better for a street car, the 39's on my car border on over-carbed.As fars as how the motor runs they are the bomb the motor sings......revs like mad and instant throttle response.
Flatslide FCR Sidedraft Flatslide FCR Downdraft CR-MX off road ruggedized Roundslide CR
FCR41 kit for oval-port A-series
Matsuoka MSR
http://www.matsuoka-m.com/web/carburetor
MOTOR SPORTS PRO SHOP まつおか
Matsuoka MSR are like FCR but about $1000 US cheaper. They use the same sliding throttle valve design. They're made by Mikuni. Manifold can be any DCOE (Weber/Dellorto/Solex) type.
new, jetted to your spec: 96K yen (1230 AUD) or with manifold and linkage closer to 200K yen.
Feral said:
When I say just about as good as injection I mean the low speed response from the Mikuni flat slides is incredible. It will still not be as accurate as any well laid out injection system, but really do work very well
MSR Flat Valve 42 mm 238,000 MSR Flat Valve 45 mm 258,000 MSR Flat Valve 48 mm 298,000
Mikuni
Mikuni also made constant velocity (CV) carburetors. The venturi size is what sets the HP characteristics. CVs use the same bore size as venturi size except for a fixed obstruction to generate vacuum.
Mikuni BS series. For example 1980- Suzuki GS1000 came with BS34 carbs (34mm) for 90 HP. A 1981 Kawasaki KZ1000 fitted with BS34s made 102 HP.
Mikuni BS series variable venturi constant velocity design Side draft
Mikuni BD series Downdraft
These being CV carburetors are similar to SU carburetors. They have a traditional butterfly throttle but the actual airflow is controlled by the round slide (piston) that floats up by vacuum action. It is opposed by the dome spring.
Flat Side * Mikuni RS * Mikuni HSR * Mikuni TM
Flat Slide
VM
Mikuni VM - late model round-slide series http://www.mikuni.com/pdf/vmmanual.pdf
VM28 may be ideal for a stock A12 (see Carburetor Sizing) - and are only $100 each.
BDST
BDST D=Downdraft CV constant velocity
BDST36 is the famous Honda CBR600F3 carburetor 85-100 hp (F1 used 32 mm carburetors)
BDSR
BDSR D=Downdraft R=Radial slide
BDSR40 is the famous Yamaha R1 carburetor 150hp
BS32
Mikuni BS32 was chosen by Nissan to power the A-series engine in the 1970 Sunny Cab (model C20).
16010-G0301 BS32-5A [from '69-7] 16010-G0302 BS32-5B (from '70-1)
16189-G0320 JET-slow No. 45 16036-25522 JET-slow air bleed No. 210 16296-G0320 JET-air, 0.8 diameter 16033-G0340 JET-main R170 16295-G0320 JET-enrichment, No. 50 16346-G0320 SPRING-diaphragm 16353-G0320 SET-needle 16354-G0320 NEEDLE-jet
16546-G0300 Air Cleaner ELEMENT
BS34
90 hp 1980- Suzuki GS1000 102 hp 1981 Kawasaki KZ1000 SX650 1989-1984 * 132.5 main jet * 2.5 pilot jet * Y-O needle jet * 5HX12 needle
BS34s are rather forgiving and will at least run most engine set ups with stock jetting. W
The pilot air jet is removable, and the main air jet is fixed.
3 main circuits of the carb * slow speed or idle (mix screw and pilot jet) * midrange (slide, slide needle, and needle jet) * high speed or main (main jet)
These all overlap the circuit next to them and changes made to one will slightly effect the other
Float height on the brass floats is 27.3mm. For later units with plastic floats, 22 mm. +/-1mm. BS34 are are fitted with drain valves opened by a screw, with a hose nipple on the outlet. To read fuel level, attach the sight tube to the outlet and set vacuum petcocks, if fitted, on "Prime," and open the screw until fuel flows into the sight tube. With the motorcycle level, hold the sight tube upright beside the carburetor body. Fuel should rise in the tube no higher than the lower lip of the carb body where it overlaps the float bowl, and no lower than 2 mm. below it.
The pilot circuit fuels the engine in low-speed operation, when the slide is lowered.
real Mikuni jets are availible . Get them from the stock size up to two over on the pilots and up to three over on the mains. Follow the guide and test them to see what your engine needs. http://www.amckayltd.com/carbguide.pdf
Tuning kit * Pilot jets * Needles * Main jets
BS34 Jet Needle
5IX11 richer 5HX12 leaner
Needle Jet
Needle Jet Y-O 336-Y0
Yahama 1200
Photo Index
fcr,msr,keihin,cycle carb,bike carb
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