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Discussion Starter #1
hey guys. im having a bit of trouble with my mikuni 28's. they leak from the overflow tube at the bottom when the bike is sitting. i've got no idea why. how do i fix this. im loosing a shit load of fuel this way. any clues? thanks all in advance

cheers

hely
 

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take em off unscrew the bowl check floats / needle and replace if necessary. If the needle is spooged then it is no good.
s
 

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Yeah, either the floats have sunk, ie leaked gas inside the floats, or the float valve has dirt or is sticky due to sludge. It might be that the float pivot has also gotten sticky from sludge if they've sat around with fuel in them for a considerable time. Just take them apart and clean. Replace the needle and seat (float valve assy) cuz they're cheap and its easy to do and are most likely the problem.

breathe deep when you do it and you might get a little dizzy. Doesn't last too long and you can get a good headache later but at least it's legal.

Mike O.
 

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my little rieju was having similar problems last season. the float was not set at the correct heigh/ level...... so the carb would not stop filling with fuel. also the small clip attaching the needle to the float was causing the needle to hang up and not properly seat. totally weird. after an hour or so fiddleing with it and arguing with my father in law about it... the problem was solved. bastard carbs

matt
 

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if you run at wot like donovan, it doesnt matter. just fill it, start and dont back off til its empty.

right j not d???


jc
 

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Discussion Starter #6
im really new to mikunis and im worried that if i start messing with the carbs that i wont get the bike to run again. i just finished syncing them this last weekend and that seemed to make a big difference in the acceleration and starting her up. im idling high right now at about 2500rpm and have to run the carbs with the choke on. if not, they want to bogg down and die. im jetted way too rich and so i've got sluggish low/high rpm. if i wot right off the start it will bogg and then pick up. however, if i gradually increase the throttle, she takes off like a rocket. i was going to just take the RD to a yamaha place near my house and have them tune the bike. they are going to charge me about 2.5 hours or so so im looking at about $250 for the job. think i can do this myself? i've got a tuning manual for mikunis but like i said before, im new to them and am not super comfortable with them. i've got a set of jets too that came with the bike that range from 180-220 for the mains. i think the idle jet is too rich and the main is too big though. the bike's got some expansion pipes on it so it's up jetted right now but i think the po got a little over zealous with it. anyway...what do you all think? try it myself? or take her to yamaha?

cheers

hely

74 Yamaha RD350 cafe
 

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do it yourself. the worst thing that can happen is that you will have to do the job 3 times. either way you can keep $250 in your pocket and you will have learned something. if you have the mikuni literature... you should be able to adjust them properly.

besides, half the time you bring a bike to a moto shop..... they just don't have the same interest in the machine as you do. they want to make money. you want to make your bike purr. make it purr.
 

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Yeah..there's a ton of RD tuning info on the net. You should be able to get REAL close with off the shelf info.

If you have fuel coming out of the overflow then you have a float/needle problem like everyone has said. That is one reason you are rich...assuming you are rich.... as float level goes up...carb runs richer.
Although the fact that it only runs with the choke on usually points to a lean condition....unless there is a high idle linkage.

If the bike is new to you...you need to do the whole deal...pull the carbs and rebuild if necessary...check the timing/points/condensor etc.
You gotta learn the bike eventually anyway.
JohnnyB
 

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Another thing to look for is a crack or air leak in the rubber manifolds that hold the carbs. That can cause high idle and erratic throttle response.
As the others have said, you can do it...

FR
 

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Discussion Starter #11
right on guys. actually the high idle is from when i synced the carbs. i put the idle a little higher so that when i take off in first the bike doesn't bogg as much. that way when im taking off in 1st, the rpm's drop but im still at 1000 you know? anyway...im going to check with my local place and see if they've got a needle kit on shelf. i tend to learn best from watching the first go around but i think im going to give this a shot. thanks all for the advice. i'll let you all know how things go.

cheers

hely

74 Yamaha RD350 cafe
 

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hely,

check out (google) sudco. they are in cali too!

texy

"who's scooter is that?"
"joe clancy's"
"where's joe clancy?"
"sleeping!"
 

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quote:
right on guys. actually the high idle is from when i synced the carbs. i put the idle a little higher so that when i take off in first the bike doesn't bogg as much. that way when im taking off in 1st, the rpm's drop but im still at 1000 you know? anyway...im going to check with my local place and see if they've got a needle kit on shelf. i tend to learn best from watching the first go around but i think im going to give this a shot. thanks all for the advice. i'll let you all know how things go.

cheers

hely

74 Yamaha RD350 cafe
I assume the mukunis you are dealing with are VM series carbs. Here is how I synch them on my triples. The method usually gets me so close that a few times I did not need to make any adjustments.

With the bike off I stick my fingers in the carbs to feel the slides. I then adjust the throttle cable so that both slides move up at exactly the same time (use the slide that moves earliest as the baseline for no throttle slop). I then reset the air bleed screw to the factory setting (should be 1 1/4 turns out but check the manual). I then start the bike and using that baseline carb I adjust the other carb until the blue smoke pulses are equal. Takes a lot of time and the easier way is to just get a carb synch tool and do it by the book but that takes an investment of money and my way is free.

no, SET YOUR IDLE BACK TO NORMAL. you should not run any two stroke street bike with a high idle, good way to overheat it and burn it up.

As for your bog...it's a fucking two stroke. They have no power whatsoever until you hit the powerband. They are supposed to bog off the line and be slow until you hit the band. That is what makes them so fun you go from making no power to full torque and hp within 200 rpms (not 200 rpms off idle, but at 2800 rpm you are still making no power, at 3000 you are almost at your peak power). RDs and Kawi triples have literally no balls until you hit the power band, it is just how they are, suzukis are a little different in that their powerband is really early but then again suzuki had a buffalo while kawi had a widowmaker.



here is a link to the manual on mukuni vm carbs:

http://www.mikuni.com/pdf/vmmanual.pdf

Edited by - Geeto67 on Mar 26 2006 6:32:04 PM
 

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what he just said. If it didn't fall on its face off the line, I would start looking for valves in the wrong place. To avoid the bogging, you have to learn how to get one of the line, so set the idle where it is supposed to be. Ask Zach how to get a smoker off the line,quick before he rides that R6 and forgets.

Anyway, try sending mail to Stan Lippert from WERA or post on the WERA BBS and maybe he will see it. Either him or Lyn Garland from WERA can tell you what you should have in there. An RD comes stock with 28's if I remember, so set the jetting at stock to start off with, then go from there.Your local Yammy shop won't be any good unless they have a mechanic over 40. Anyone younger than that has never ridden a street two stroke, and dirt bikes don't count.

Easy way to check float shut off height is to take the bowl off. The flaor needle is actuated by the big u-shaped metal flapper, that sits on top of the floats. For all Mikuni round slides, the gas should sto flowing when that u-shaped dealie (don't know the real name for it so don't make fun of me) is parallel to the bottom of the carb body. Turn the fuel on and manually shut the float needle with the u-shaped whatchamacallit. If it doesn't shut off when its parallel, bend the little tab that actaully touches the float needle until it does, then you are done. It takes longer for me to type this then it will for you to do it. Do this on both sides.

Start with taking the carbs completely apart and cleaning them first. Makes life easier.

Bike should run without the chokes on. You'll never get it off the line if you have to choke it to ride it.


Chris
 
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