Hello guys,
newbie here.
i own a 2013 yamaha lc 4 speed.
i read about CJ IPOH MB 28mm exhaust standard cutting (same design as original yamaha exhaust)
can i install it to my standard (no modifications) bike?
is there any bad effect after i install it ?

Guys, i need to know about air/fuel mixture screw setting for stock lc v2 4 speed. anybody knows please tell me. how many counter clockwise turns from the fully closed position? it is hard for me to find the stock setting because of new carburator that lc v2 use is mikuni bs25. it has rubber diaphragm that controls the needle jet. so, if you twist the throttle, it would have some delays before the air/fuel mixture being suck by the piston.

thanks.

yes. i changed from stock paper air filter to high flow air filter. now i set the air/fuel screw to 5 turns out from fully closed position.

yes. i know that. this is why i'm asking here. hope you guys can help me to find perfect setting for mikuni bs25 carburetor.

on the left side of mikuni bs25 there is a screw located near the intake manifold. is that fuel screw or air/fuel mixture screw ?

thanks for the tips!
i just know that screw which located near the intake manifold is FUEL screw. this mikuni bs25 is not for performance but i has good fuel consumption.
i just changed the stock paper air filter to a high flow K&N clone air filter. then i set the carburetor fuel mixture screw (this screw located near the intake manifold) to it's fully close position. i started the bike and set the carburetor idle to 2000-3000 RPM and open the fuel mixture by turning it counter clockwise until i hear the bike revving to it's maximum RPM. it is about 3.5 turns counter clockwise from the fully close position. after that, i added 1.5 more turns from the 3.5 turns position. means 5 turns out. im not sure if my setting now is lean or too lean or rich or too rich.

i think yes.
i also changed the stock exhaust to a 28mm manifold exhaust.
this is why i kacau the stock carburetor setting.
if we set the carburetor too lean, the engine will be easy to start on cold temperature, but the combustion chamber can be hotter so not suitable for long distance and it also not good for spark plug.
if we set the carburetor too rich, it will be hard to start on cold temperature because fuel is more than the air but good for long distance and also not good for spark plug.
i'm looking for balance between this 2 conditions.


waiting for bro alexei to answer the question.

This post has been edited by piju: May 9 2014, 12:35 PM

you lc version berapa ?
carburetor apa ?

air filter racing tu macamana ?

thanks bro for the detail explanations.

now i understand that choke means to richen the fuel mixture by choking the air.
so, my max RPM i can hear is starting from 3.5 turns and above until 6 turns. after that it will get low again since fuel is more than the air. is it the best for my FUEL SCREW setting is at 3.5 turns only ? not 5 turns ?
i need to know which is the optimal setting for my fuel screw with KNN air filter installed first, after that i will check my spark plug condition later.
BTW bro alexei, i am a little bit confuse here since some people said i need to set the idling engine at 1100-1550rpm before setting the fuel screw, and some said i need to put engine idling rpm to 2500-3500 rpm first before setting the fuel screw. which one is the best method for mikuni bs25 carburetor ?




these picture is my guide later.

bro alexei, about the exhaust, it was 28mm manifold with standard muffler same design as stock. better sound than stock exhaust. but not too loud

This post has been edited by piju: May 12 2014, 03:47 PM

what do you mean with "add another 1~2 minutes of a turn" ?

thanks for explanations again bro. actually my primary intention was to find the good optimal setting for fuel screw only. i am not planning to reposition jet needle now. maybe later.

and i understood what you tried to say, it is like after tuning the fuel screw, i need to drive my bike and feel the acceleration by trying all degrees of throttle positions.
right bro alexei?

thanks bro,
now i understand that i need to tune my carb again.

i will close the fuel screw, open it to 3.5 turns and play around with 1~2 minutes turns.
maybe i need to open or close more or stay at 3.5 turns right bro alexei?
however, i need to set and play with the throttle first. different bikes and riders may comes with different result i think.

btw, bro. which is the best way to increase RPM ? is it by turning the idle screw or just twisting throttle using hand ?

This post has been edited by piju: May 14 2014, 03:02 PM

btw bro alexei, quoting your previous reply. you said "normally after you get the max RPM, is richen a little bit",
so, im here asking why do we need to open 2~3 minutes more ?

i see, thanks for the info.
just now i set my fuel screw to 3.5 turns and added 2~3 minutes more. idle RPM quite good. throttle respons also good. but when i ride the bike and feel like some bog and hesitant happened when the bike is high RPM on gear 2, after i shift it to gear 3 then it's ok. is this happen because im using high flow air filter?

(i assume than when higher rpm, the combustion chamber will produce more pressure to suck the air and since im using high flow air filter, the air will enter more than fuel, this is why bog and hesitant happened)

thanks for the advise, i have already readjust the fuel screw. i added more than 3.5 turns. i think it is 3 and 3/4 turns or more. but not more than 4 turns. throttle response on low RPM seems good. but i need to ride the bike at higher RPM to know the results on higher RPM response.

yeah. thanks to you too my brother.
now i readjust the fuel screw again. i set the idle screw until i hear high revving and after the adjustments on fuel screw, i reset the idle screw now back to normal. maybe on 1200-1500 RPM i think, i dont have a takometer to measure the RPM. throttle response quite good on lower and higher RPM. my bike is energetic same as the fuel screw on 5 turns out position. i dont have problems starting my bike either it's in cold or hot temperature. morning starts never had problems. i'm not sure either my setting now is rich or lean. let me bring along a screwdriver with me when i ride the bike tomorrow. if i feel any bog or hesitant either on lower or higher RPM, i will adjust it by opening more or closing back the fuel screw. i will keep you posted about the results later.

alexei

i think i know what is the biggest problem tuning mikuni bs25 carburetor. it is because of the low restriction air filter. i think i solved the problem by reinstall the stock paper air filter and retune the fuel screw until i hear maximum RPM.

if i still want to use the low restriction air filter, i think i need to rejetting the carburetor to compensate the air. as i know, the perfect combustion will need 14.7 air and 1 fuel. means 14.7:1. if we allow more air to enter the combustion chamber, then we need to allow more fuel by rejetting the carburetor. this is critical on higher RPM but not critical on idle and low RPM.

if we allow more air and more fuel, means we are dropping the fuel efficiency. we still dont know either the combustion chamber can handle the burning or not. if it can handle, then we will get more power. if it dont, means no perfect combustion then we will have fuel efficiency drop and the side effect is our piston maybe dirtier than before.

am i right bro alexei ?

This post has been edited by piju: May 17 2014, 06:31 PM

ok bro alexei maybe i need to do a lot with mikuni bs25 if i want to use it with high flow air filter. or else, change the mikuni bs25 with the vm22 carburetor. now i know why people change their yamaha lc v2 carb to v1 carb. it should be carb first, then the air filter change.

for EFI systems, or normal type carburetors, i believe that using high flow air filter will improve their torque and HP. maybe not for vacuum operated carburetors like mikuni bs25.

the yamaha v1 carburetor which is mikuni vm22 operates differently from mikuni bs25. for the vm22, throttle controls the needle jet. so if we twist the throttle from close to maximum opening, you will force the engine revving from low to high RPM.

for mikuni bs25, throttle controls the butterfly valve. not needle jet. if we twist the throttle from close to maximum, it only allows more vacuum pressure to the rubber diaphram for liftting the needle jet. we cant force the engine revving to the max, it will do by itself, slowly.

if we install high flow air filters on mikuni bs25, i think it will reduce the vacuum pressure and slowing down movements of the rubber diaphragm and it also will never reach the maximum needle jet opening like you already said.

now i see why yamaha created bottleneck for air to enter the yamaha lc v2 air filter box. to create high pressure for lifting the rubber diaphragm.

what say you alexei ?

This post has been edited by piju: May 17 2014, 07:45 PM

bro alexei,

i have already retune my BS25 and reinstalled the stock paper air filter.

i warned the bike, and then i closed the fuel screw to it's close position. i opened the fuel screw for 1 turn and started the bike.
then i opened fuel screw 1/4 turn more and listen to the RPM. i end up with 2 and half turns. on 2 and half turns, the bike started to rev on higher RPM. when i open more, the RPM stays high. when i open more and more, the RPM went down. so i closed the fuel screw again, and yet end up on 2 and half turns. i assumed that on 2 and half turns position. the bike reach it's first maximum RPM level. i added more turns, maybe about 3~4 minutes more. total turns maybe 2 and 3/4 turns.

is this the correct way to tune ? i'm not sure is my setting now rich or lean. could you clarify me bro alexei ?

thanks

sorry bro alexei, i didnt mentioned that after i warned to bike, i set the idle screw to higher RPM than before. maybe around 2000 - 3000 RPM.
am i on the right way tuning the carb bro? am i getting the best and optimal setting result ?