how do u no if ya motor is running lean?

[sik-pj]

hey
all i just wanted to no something.... how do u no if ya motor is running lean??
thanks

 

[Fenton]

it may like kind of stutter? at high rev like its not getting enough fuel.
in some cases might be running a little hotter.
you do understand what lean and rich is?

 

[sik-pj]

lolz it was just a que my mate asked my mates bike sounds like its geting no petrol at times how does it make it run it better then lean like how do u fix it

 

[Fenton]

yeah when a bike is running lean it means that there isnt enough fuel in the fuel/air ratio, when its rich it means theyre is more than enough fuel.
On the carb its just a simple screw, screw it in to make it lean, or out for it to be rich, make very small adjustments at a time and always be sure where it was positioned before you turned it.

did that help?

 

[sik-pj]

ye thanks but when i do it... it revs high is that the screw on the side of the carby??

 

[tassy]

not all carbys have leen and rich adjustment screws on em

 

[sik-pj]

well my carbs a mikuni 25mm

 

[NinetySix]

the idle mixture screw is underneath the carby, the idle speed adjuster is on the side.

thing is, the idle mixture screw only affects the mixture at very small throttle openings - anywhere in the rev range.

if its running out of fuel in the top end with the throttle wide open, then its a problem with the main jet or maybe the needle. best bet is to pull the carby off and pull it apart, give it a good clean out... could be some crap in the main jet or needle jet. i would also make sure your fuel lines are not kinked or blocked either.

the best way to tell if its running rich or lean is to see the difference between the motors performance when the engine is cold and when it has warmed right up. if it runs like **** and doesnt go hard when its cold and gradually gets better after like 10 mins or so then its probably running lean. If its good off the bat straight away but then gets a little worse as the motor warms up then its rich. It will also run hotter when its lean, the exhaust might glow if its really lean and you'll just be able to tell from the heat comming off the engine. Rich mixture = runs cooler. If the mixture is right then it should be making its best power within a minute or two of starting the motor and not get worse as it warms up or on hot days.

if the bike wont idle or putt around easily with the choke off at slow speeds with only small throttle openings while the bike is still cold then you would need to try half a turn richer on the idle screw. thing is that is all it really affects, when you twist the throttle wide open you switch to the main jet.

If it was running good a week ago but isnt now then you dont need to rejet, just need to clean the carby or fuel lines out.

 

[sik-pj]

thanks how do i rejet it?? lolz

also my neddle is lose it moves around a lil bit is that ok? its noy going to come off but its abit lose

 

[NinetySix]

i cant help but notice your sig says you have already rejetted your mikuni?

the easiest way is to change the height of the needle... take it out and move the E-clip down on notch so that the needle sits slightly higher (and lets more fuel in)...

the needle height mostly affects the midrange 1/2 to 3/4 throttle range, but slightly affects top end... if the top end full throttle feels better but the midrange no better or even worse then maybe go buy a main jet one size larger. if it feels better overall then just leave it, but if you need a bigger main jet then the needle is just a bandaid fix.

there are 5 notches on most needles, and you should only really use the 2nd 3rd or 4th notch... if it runs best on the 5th notch then thats a pretty good sign you should go up a size on the main jet and then set the needle back to about the 3rd notch. experiment, have fun. dont have to pull the carb off to take the needle out on my bike so its not too hard.

the spring should hold the needle in place when its installed in the carb... theres a big clip that pushes down on the needles E-clip and the spring pushes down on that... its ok if it wobbles a tiny little bit, but not like a few mm... shouldnt be much up and down movement either.


if you want to be confused further, have a look at this:

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,KeihinFCRTuning_EC997_4gasEGA.htm

 

[sik-pj]

thanks mate for ya help. i swaped carbys now so i need to re jet it again howmuch are the bigger jet for a 25 mm mikuni?????

 

[NinetySix]

jets are probably about 3-4 bucks each

play with the needle first tho, saves a lotta time and effort

 

[sik-pj]

lol call me dumb wat u mean play with the needle? lolz check ya pm i sent u somethign

 

[NinetySix]

dumb lol