Minuki carby tune up.

[cass38a]

My bike (125cc Lifan) starts first go and runs perfectly in most conditions but...... when you twist the throttle real fast to 100% it dies momentarily. If you open it a fraction slower it accelerates no problem. Does anybody know what I can do to sort this?

 

[CHINGArider]

Try moving the needle clip in the carb down a clip or two if its not allready on the lowest setting.

 

[PICCOLO]

yeah thats what i would do and maybe some jetting

 

[tubes380]

which way do you move the needle to richen the mixture up or down, and will this fix his problem cos mine had the same prob but now i have an irk it doesnt do it at all.

 

[sik-pj]

mine gets real hot after rideing 20mins or so... do i need to turn the mixture or is that normal

 

[Trashthumpy]

that means its running lean so richen it up abit

 

[sik-pj]

ryan u talking to me?? mate

 

[NinetySix]

hot = lean, usually.

if you move the clip on the needle one notch towards the point of the needle (so the needle sits higher in the throttle piston) it will let more fuel in, thus richer. move the clip towards the top of the needle and it will let less fuel in too

have a look at the idle screw too tho (usually at the front of the carb on the bottom) which is probably more likely to make the bike run hot than the needle, especially if your just putting around or even idling it

 

[CHINGArider]

have a look at the idle screw too tho (usually at the front of the carb on the bottom) which is probably more likely to make the bike run hot than the needle, especially if your just putting around or even idling it

I think youre talking about the mixture screw, the idle screw is the one on the side of carby.

 

[mjc85]

have a look at the idle screw too tho (usually at the front of the carb on the bottom) which is probably more likely to make the bike run hot than the needle, especially if your just putting around or even idling it

I don't think the idle screw would have anything to do with the engine being hot, it's definately running too lean.

When I installed the new bigger pipe on my bike and started it for the first time there was alot of heat coming from the engine and pipe onto my legs. So I moved it to the richest setting and its a better but it still needs to be richer.

 

[NinetySix]

yes idle mixture screw, not idle speed adjuster screw. running lean at idle while your not moving will make any motor run 10 times hotter than it should.... running a little lean at WOT while your belting along wont raise the temps quite so much

 

[mjc85]

yes idle mixture screw, not idle speed adjuster screw. running lean at idle while your not moving will make any motor run 10 times hotter than it should.... running a little lean at WOT while your belting along wont raise the temps quite so much

The mikuni's on most pit bikes don't have a mixture screw.

 

[sik-pj]

if the bike is running lean does it make any power diff thanks mate

 

[THUMPY125]

The mikuni's on most pit bikes don't have a mixture screw.

yes they do its tucked up underneath the carbi close to the cooling fins on the barel. hope this helps.

 

[NinetySix]

butt slammed

 

[PocketHead]

how was it?

 

[pitboss125]

My bike (125cc Lifan) starts first go and runs perfectly in most conditions but...... when you twist the throttle real fast to 100% it dies momentarily. If you open it a fraction slower it accelerates no problem. Does anybody know what I can do to sort this?

I have the same problem with my bike. i tryed moving the clip on the needle and it didnt help although it made the bike run better. Does anyone have any other ideas on how to fix it... (when i hit the throttle really quickly and turn it to 100% it just dies) but when i do it a bit slower it is fine. Does anyone know wat cause's this?

 

[cass38a]

Yeah I moved my clip around today (tried up and down) and it probably made it worse. I ended up putting it back on the second lowest clip where it was in the first place. any other idaes?

 

[NinetySix]

have a little play with the idle mixture screw too perhaps...


but these are flat slide carbs, your not really supposed to just whack the throttle open at idle.


also one other tip, my carb didnt have any washers above or below my needle and even with the spring pushing down on it, it could still move up and down just a bees dick (like 0.25-0.5 of a mm) which means under load with vibrations it doesnt give a smooth delivery... i put some tiny washers in and it doesnt move at all now, and its a bit smoother

 

[Mack]

Mostly those 25 Mikuni carbs need a bigger main jet. You will get them to run alright with the needle clip all the way at the bottom, but that is just a sign to go up a size or two on the main jet.