but i read in a mikuni manual that even though theoritically it is 15:1 afr..but max power is generated at 12:1 ratio of air and fuel....

There are a whole heap of factors that influence combustibility of fuel like manifold design and number of valves but whatever it is 12 : 1 is way to rich. A few turbocharged cars go as low as 11.5 : 1 but for a naturally aspirated motor I wouldn’t go anything lower than 13.
At the end of the day performance does the ultimate talking. I richened a Jaguar to 11 : 1 for it to idle well, which resulted it in making half the power it was supposed to produce.

just check your spark plug to see ur engine state of tune . it will tell if its rich or lean

i checked both my plugs a week back... they were clean...

but checking the plugs to find if my bike is running lean or rich is a long procedure.... i would have to ride a distance to get my feedback.... i was looking for some realtime response... something like a speedo or a tacho.... is any such tool available to have realtime feedback to show it??

it will always be better(and cool!!) for the bike to give me some feedback rather than i coming to conclusions...

Ok people stop talking about jets and swapping them. I am asking whether the VC screw can make my bike run lean. So lean that the engine heats up.This has been a problem which i am facing since a few days. I thought it was due to bad engine oil. So I changed the oil with brand new 1 litre castrol power 1. The engine is still heating up. So i guess I am running lean.

I was asking about the VC screw just because I wanted to narrow down my troubleshooting.
I am facing a overheating problem after riding just 8 or 10 kms that to at average speeds of 40km/hr to 50 km/hr on appropriate gears.
Overheat as in I can feel the heat near my calf while riding the bike.

IMO overheating of the engine is caused mostly by bad engine oil or lean mix right?
Bad engine oil possibility ruled out.
Any solutions/suggestions?

How did u check for overheating mate? Any instrument was used? Mostly what we feel as over heating is psychological.

BTW,incorrect valve/tappet adjustments also lead to over heating.

No valve or tappet settings were ever done. My bike is just 4300kms old in 10 months.
So i too guess the heating is normal. Rest all is fine with my bike. Accelerates normally, the speed and the RPM are in proportion[implying no clutch damage],new engine oil,etc.So i guess i should just stop worrying right?


BTW insanebiker are you from Mumbai?

Then dont worry about it buddy! The SVC guys have some kinda instruments to check the temperature,and see if it is in the permissible range. They also have a stethescope to check for unusual noises.

Please tell me in what steps should I vary the VC screw to get the right ratio?
I will tighten the screw all the way inside and then unscrew it one turn at a time. The service manual says the VC should be set at 2.5 turns(+/-2 turns outwards).
I set it at 2.5, the silencer makes dhup dhup sound when RPM drops after revving hard[say upto 5.5k rpm to 6k rpm (not in neutral)] and releasing the accelerator.The RPM does not fall smoothly. It makes this sound. So I unscrew the VC by 2 more turns [now a total of 4.5 turns]. The RPM falls a bit smoothly with an occasional dhup dhup. But I dont remember such sounds when the bike was relatively new. I unscrewed the VC by another turn[total of 5.5 turns]. The dhup dhup is all gone. But the acceleration is sluggish in all the three settings[2.5turns, 4.5turns,5.5turns].Does this mean that the mixture is still lean??

I checked the number of turns on a friends 3 month old p180UG3. It was set to 9 turns.Yes 9 turns. He said he or anyone else for that matter never fiddle with the carb. I took a ride of the bike. It runs just perfect,like the way my bike used to run some time back.

Please people help me.This carb thing has gotten into my head. All I see everywhere are carbs!!

did you try the 9 turns thing on your bike then ?

Today I went for a long trip. Got some nice stretches of roads. I was running on 8 turns. The bike refused to go over 98km/h. No matter for how long i held the accelerator at full throttle position, the bike refused to go over 98.So I guess I am running damn rich!


I am in a fix right now.if i set it to 2.5 or 3 or 4 turns the silencer makes a dhup dhup sound. the RPM doesnot fall smoothly, there's some kinda interruption in the sound with the dhup.
is the dhup normal?
i don't remember such a sound when the bike was new.
should i set it to 2.5 turns[as mentioned in the service manual] and don't give a damn about the dhup dhup?

Look here for how to read a spark plug.