G'day R/birds, hope all goes well with the build. I strongly recommend disk brakes, welding mounts is no harder than posts & theyre much safer. I had front disk only but have now fitted disk rear wheel. I need to weld the mount also, as well as attach points for tank, motorcycle led indicators & the x chamber once tuned. I'll run motor in first. I need to replace the rear wheel gear/freewheel cassette. Its been dicey for ages but it didnt matter with the stock setup. Since fitting the shift kit it has started to fail so no riding for the past week. Ratios are 13 to 29, 7 speed. The new rear wheel is an 8 speed, I used a spacer to fit the 7 speed cassette but will fit an 11 to 28 8 speed cassette this friday. Keep you informed. Cheers mateAnyone using a Mikuni VM16 ?
- Thread starter Ratchetbirds
- Start date
Hi Rachetbirds, hows the bike progressing. I have fitted new 8 speed cassette. I made a mistake with the ratios last post. Its 11 / 30 Hyperglide & with 11 on right side of the jackshaft gives nice spread,, lowest will pull anywhere & a tall top. I've taken it to 60 ks, it'll do a good bit more when run in, its still pretty tight. The guys at rocksolid are machining up a manifold to fit the Mikuni without using the plastic shim, OD 25mm with the end 4mm turned to 21mm for the Oring built into the carb. I'll probably order one of their billet heads in a week or so cant wait, & I'll try & get pics posted when done. Cheers mate
i've got my mikuni back up and running on my race bike. weird thing, is it's running lean now, whereas on my old bike, it ran rich. the only different thing on the motor is an expansion chamber.
i might have an air leak somewhere. haven't had time to dial it in...
i might have an air leak somewhere. haven't had time to dial it in...
Hi Bairdco, hows it going. Fitting an expansion chamber will nescesitate a carb retune. You're using 16mm mikuni right? What size jets, needle, slide have you had to use to dail it in, & what is done to the motor. Mine has the stock port arrangement except for a cleanup of casting burs & stock head at the moment, tho will shortly have a hi comp billet head & an sbp expansion chamber matched to the port. Cheers mate
i was having a lean condition and hard starting on my mikuni vm22 it was the float level!! had the carb on to much of an angle i believe the mikuni vm carbs can run up tp 3/4 throttle without even using the main jet.. at least thats what i read..
glenn
glenn
22mm is a very big carb for a motor this size, but if you're getting a good plug color well & good. I havent fitted the carb as I'm waiting for a manifold but tuning proceedure s downloadable from mikuni's web page. They are started throttle closed as there is no choke, rather a tuneable start circuit, the slide closed acts ensure the motor draws thru the idle & start circuits. Cheers
Hey guys, the manifold you's are using to mount these carbs is a straight shot to the jug, right? Can anyone tell me the overall length of the manifold? No problems physically fitting the carb in there? Just eyeballing it, it looks like it'll fit but might be close. I plan on rerouting the clutch cable to a tab mounted between the top & clutch cover side mounts on the shift kit. I have figured the manifold profile for the O-ring to seal on as end 2mm OD 17mm, next 2mm OD 21mm &manifold OD 25mm. Cheers
offhand, i don't even know what the jet sizes are, they're all stock from when i bought it new at a swap meet for 5 bucks.
on the first bike i put it on, it was running so well i never bothered to re-jet.
on this bike, it's a grubbe gt4 straight plug head, reversed barrel, modified sbp pipe, trimmed piston skirt, and pretty much everything else i could think of to do to this engine.
i'm gonna keep messing with it, buy some jets, etc...
here's a pic before swapping the gt5 out with an older gt4:
on the first bike i put it on, it was running so well i never bothered to re-jet.
on this bike, it's a grubbe gt4 straight plug head, reversed barrel, modified sbp pipe, trimmed piston skirt, and pretty much everything else i could think of to do to this engine.
i'm gonna keep messing with it, buy some jets, etc...
here's a pic before swapping the gt5 out with an older gt4:
the frame is a slighty modified Colson Double Bar Junior. made in ohio in 1936,37.
here's the build: http://motorbicycling.com/showthread.php?t=36139
here's the build: http://motorbicycling.com/showthread.php?t=36139
I just bought and installed a mikuni vm 16 on my bike and ill share what I have done .First off I had to make a manifold for it , The carb came with a 70 main jet . I thought that might be to rich so I went out looking for smaller jets .I found a few and started with the 70 that came in it .
The bike started and idled well but anything over half throttle it would bog. I flipped the choke on while riding it home and it ran better so that told me it was lean . It was late and the biggest jet I bought was only a 72.5 . I started scrounging and found a few more jets from a pit bike I have but they were a 96 and a 100 jet I threw in the 96 to see if it would run .
What a difference that jet made bike runs really good now from idle to full throttle . I am sure it could use some fine tuning still but it does not four stroke at all . Idles really well and has a snappy throttle response on the stand .
The bike started and idled well but anything over half throttle it would bog. I flipped the choke on while riding it home and it ran better so that told me it was lean . It was late and the biggest jet I bought was only a 72.5 . I started scrounging and found a few more jets from a pit bike I have but they were a 96 and a 100 jet I threw in the 96 to see if it would run .
What a difference that jet made bike runs really good now from idle to full throttle . I am sure it could use some fine tuning still but it does not four stroke at all . Idles really well and has a snappy throttle response on the stand .
Awesome work Headtrama. Thank you for posting your pic and experience with your carb. Gives me a whole new perspective on jets for my carb. I wouldn't have thought to try a jet that much larger but now I will.
Today I messed with it some more , It had a slight stumble off idle . I bought some more jets and went down to a 92.5 jet . I let the bike fully warm up and turned the air screw out until i got the highest idle from it . It's about 1 3/4 out from seated , took it for a ride and the bike runs perfect now . The stumble is gone pulls hard and sounds crisp . no four stroking anywhere. It has a very smooth idle and snappy throttle response now . The needle is in the center where it is suppose to be . Try going richer on your jetting Ratchetbirds.
That is exactly what I am thinking. Richen it up.....alot. Have you canged any of the other internals? Air jet and such? I can't tell you how much your posts have helped me on my carb set-up. Just gotta get the frame painted and finish mounting my shifter kit and x-chamber. Also upgrading some of the components in my CDI then we are ready to mount the carb again.
Everything is the way it came out of the box except for the main jet. I have been riding this thing every day trying to get some miles on it before the up coming race. I have about 45 miles on it now and so far so good .
hi Rachetbirds, hows the build going. I got my carb mounted & tuned, Headtrauma made the manifold & did a fantastic job. My carb has 5 bleeder holes in the needle jet. Required 72.5 main & the stock 25 pilot jet. Run great. Have fitted rocksolid head. Am about 1/4 way thru the 4th tank of fuel since motor rebuild & fitting all other components,, have put about 3/4 tank thru it since fitting head & carb & have had it up to 65.1kph by phone gps app so I expect it'll loosen up a bit yet. Its a great carb for these motors, very responsive all thru the range. Cheers
By the way guys, I dont want to mislead anyone, the bike wont maintain 65k's, I can reach that after a slight downhill then a long flat that is protected from wind etc, where I can let it wind out,,, good for doing plug chops. I can maintain around 57kph,,, til I hit a headwind. I have found that its better to use 6th gear (shimano hyperglide 8 speed cassette) as top, it doesnt really have torque for 7th & 8th. Cheers guys