I'll have to check my carb tuning then..should I clean the carburetor or will tuning alone will suffice?

Sent from my ST18i using xBhp Connect mobile app

as you mentioned that you were riding with a pillion, i believe that to be a major reason for not being able to go beyond 115kmph.
check the speed again when riding single.

as for varying RPM, i am a bit confused cos i never had this idling issue on my 180. i have just resurrected 2007 200dtsi. which did have erratic idling, i had to change the coil and cdi( as the previous owner had put local, plus, the cdi actually gave up while coming back from office one fine day) though this i believe was not the cause for erratic. it was better, but not to my liking. engine did seem to miss a beat here and there

i had already checked for air leaks around carb, valve clearance was checked and rechecked and the bike was running great, cold starts were perfect, no dramas at the red light while starting from stop, but i still wasnt convinced.

last option then, carb replacement!
but decided to give a last try to tune the carb

some carb adjustment and voila..
all has been smooth since, just perfect idling.
this is where things get confusing, the service manual suggests 2.5 +_ 2 turns for volume control (VC)screw, so that means a max of about 4.5 turns out
and i was running all sort of stting on these lines for weeks, finally decided to take it beyond 4.5 turns and ended up in the sweet spot of
5.5 to 6.5 turns on VC screw and trust me, the idling couldnt be better.
it has that perfect rhythm.
i beleive the reason for this could be that our bikes are being tuned more for economy thus stifling the engine.

the spark plugs are brownish in color, no engine overheating either.

you can check/try this too.

1)ride your bike for 4-5 kms, carry a small screwdriver.
2)shut the engine off. screw the volume control screw all the way in.( the small on left side, towards the engine)
and count how many turns it turns in completely, i believe it will be 3.5 to 4 full turns or 7 - 8 half turns.

3)now bring it back/out the same number of turns previously screwed in and start you engine, (i know i am using too much screwed word here, but cant seem to find a substitute , clockwise and anticlock wise confuse me )

4)slowly in half/quarter turns screw it outward.

5)Remember the counts at all time, i usually one it on paper of mobile notepad.

6)once you screw it outwards you will notice the rpm rising, at this time keep adjusting the idle screw to lower the rpm.

7)if bike starts to stall turn the VC screw inwards.

repeate steps 4 through 7.

i have fiddled with this for long, always kept a small screwdriver in my riding jacket hidden somewhere( still do) on the way to office and back and tried all settings from 4.5 to 6.5 turns.

6.5 did seem to overheat the engine, so i found peace at 6 full turn or was it 5.5 (not sure on that, will check and edit later).

and you should find a sweet spot. trust me.

as for 180, its 2003 so was running on 112.5 main jet, changed the carb with bs29 ug3 back in 2011 which has 117.5 main jet.
180 is currently running on 4.5 turns or 7 half turn as service manual advises. again no sign of engine stifling and smooth idling, no overheating and same brown/tan spark plug.

i personally dont recommend this to others, but since you are curious/keen to resolve the eratic idle , i just thought it was worth a mention.

cdi or coil going bad so early on a bike is a rare occurance, but i would advise you to get the valve clearance checked/adjusted even before carb fiddling.

Thank you very much for the suggestion. I have been doing it since a month. Initially I started at 2 rounds. Each and every quarter rotation I checked the mileage. Because mileage was a big issue for me at that time. Because my bike had 51 kmpl initially. Later it suddenly dropped to 38 kmpl after run in period. Thats why I messed with the air screw.
So accordingly for every quarter roration my milage was improving day by day. At 3.75 rounds I got 48 and at 4 I got 52 kmpl. But at 4 rounds my bike was heating much. So I again dropped to 3.75. Now I am happy about mileage. On that particular day when fz overtook me at 130 kmph. I suddenly stopped the bike and made the mixture very rich by giving 5.5 rounds. Here I got a better pickup than previous setting. By the end of the day I had got a mileage of 38 kmpl which was a least mileage I ever got. But also fuel was dropping out of overflow pipe. Now again shifted to previous setting. Now I happy to live with it. Anyways thanks for sharing your experience. I have already checked with a new cdi, which made no difference to me. Mine is UG5 model without BCU. May be it has to do something with spark timing. Please suggest a better oil other than MOTUL 5100SS/ 7100FS. Because they both are not available here. Only 3000 mineral is availabe. I used mak 4t nxt SS. It is a gradeless oil though, it was good. Only heating issue. Motul 3000 is good for me. Any other brand?

Sent from my C2104 using xBhp Connect mobile app

perfect, 3.75 is within bajaj's recommendation, if the idle is good, mileage is good no harm there.
just keep a note of the engine over heating, if too much heating, move half turn up to 4.25 or 4.5 on a new day and see if heating is any better. i mention "on a new day" as on a same day retuning to notice heating issues might not yeild noticable results as the engine is already overheated.
hard to say, but your bike might be running lean at 3.75, thus leading to overheating. its worth a try before suspecting the engine oil for heating issues.

As for engine oil, cant comment much, i guess fellow members can advise better, as i am too much biased towards Motul cant think of any other.

Just curious..during run in period, I managed to extract around 55kmpl. Recently, I went on a trip where I maintained 90kmph@6500rpm. At that speed, with the same carb tuning, the bike returned just 30kmpl..why is it so low? Any ideas?

Sent from my ST18i using xBhp Connect mobile app

Bajaj recommended me 2 to 2.75 turns in one Svc. Other told me to keep between 2.5 to 3.25. So according to me 2 to 3 is only lean because the engine overheats much. Greater than 3.5 is not lean. It is perfect mixture. 5 and above is very rich, gives power but need to sacrifice efficiency.

Sent from my C2104 using xBhp Connect mobile app

One small question...
Recently, my mechanic tuned my bike's carb as it had reduced mid performance and fluctuations in rpm. After the tuning, the bike performed well but rpm fluctuations were still present. Hence I turned the screw 1/4 turns inwards and noticed that the fluctuations were nearly zero. Is it ok to keep the present setup or should I revert to the previous setting?

Sent from my ST18i using xBhp Connect mobile app

It is perfectly ok, just keep an eye on mileage and keep checking the spark plug color occasionally. If color remains tan and mileage remains unchanged or improves, you just might have stumbled upon a near perfect state of tune .
Keep us posted

When should we check the spark plug color? Should it be hot? Have to check the mileage for the newer setting though....

Sent from my ST18i using xBhp Connect mobile app