advice please :-)

[dal]

hi guys n gals
iv got a cbr 125 copy and the carb was knacked so I got me a VM22 Mikuni 26mm . now the bike starts fine but when I get to about 60mph it starts to make a bbbbrrrrrrrrrrrrrr sound lol and power stays the same ..... is this a mixture / tuning issue or jet prob ?
I also get a buring smell when I use the lights but that's a whole dif thread all together lol thanks .... dal

[Rogerborg]

[dal]

its a Superbyke RBP

I got it as a non runner and replaced the vacuum system with a normal on / off tap and new manifold without the hole . and as said new carb . and it fired up right away .... the bike picks up speed fine but as soon as you get near 3/4 throttle the bbrrrrrrrr like a low long fart kicks in lol ... so as you let up it goes back to normal and power builds up again ..im not expecting to much but it defo has a lot more left in it but the noise stops it .. I know its not a super fast bike and its a cheap one ... iv not touched any of the screws on the carb yet , hope this give you a bit more of a idea . thanks

[Commuter_Tim]

You say you had a hole in the manifold? (I assume you mean one that shouldn't be there )

Sounds like you may still have an undetected air leak kicking in at wide open throttle?

Does it happen in all gears, when over 3/4 throttle?
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The above post is most likely nonsensical.

I ride a Bandit 600... badly.

[RhynoCZ]

''bbbbrrrrrrrrrrrrrr'' = way too much air in the mixture. Did you fit the air filter there? Is the throttle body and jet size the same as you had before?
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[dal]

the jets are the standard size what were fitted in carb as stock which I believe are 95 main jet and 15 pilot jet . and I kept with the airbox style filter .

[Rogerborg]

Mmm, it does sound (unheard) lean, but I'd plug chop it anyway. For reference, my copybike with that engine came with a 90 main jet. I went up to a 95 happily enough with the usual cone filter noncery, and later de-catted exhausts. 100 was too rich.

Hopefully not a daft question, but is the choke definitely off? I know... uh... this guy who definitely isn't me... who after a few weeks of not riding forget which way the choke worked on his Dekni copybike carb, and again on his Enfield. What a chump.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[dal]

yep choke is off .... when the choke is on it idles really fast ... the original carb was a deni PZ27 ..

il be out in the garage in a bit il pull the plug out and see what colour it is . what way would you think of turing the mixture screw . (its under the carb oh great lol)

[Rogerborg]

[WD Forte]

most mixture screws are in for lean out for rich.
the manifold 'hole' was probably a nozzle for the vac tap pipe?
we're blanking that off and going manual on the 125 we have here at the mo.
It also has an air injection port plumbed to it
does yours? and have you blanked that off too if so?
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bikers smell of wee

[dal]

Yeah added filter and cleaned tank out first ...... And no other bit for pipes that I can see .

[Rogerborg]

Huh, well, it all sounds good then.

Air leak in the new manifold? I know there's not much of it, but is it air tight? Tried spraying some WD-40 or similar onto it at idle and seeing if the revs pick up?

I'd check the main jet again just to be sure that it's clear - it does sound like a jetting problem.

If all seems good, you could knock it up to a 100 or 105, because racebike.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike