i believe the issue could be the carb itself, no other reason, but since you've checked it and feel its okay then what else could it be ??

does it tend to turn itself off under heavy acceleration or it tends to not transfer the power of the throttle to the ground ??

i think your spark plug needs a replacement !!

================================================== ===

I think you have a point there about the spark plug replacement.

Under heavy acceleration ... specially on a steep gradient when more power is required, it feels like the transfer of power to the throttle to the ground is missing. It happens briefly and it scares me and then I ease the throttle and it feels ok.

when was the last time you changed your clutch plates chief ?

Forget the spark plug.Get the carb tuned properly ,obviously it looks like a carb problem.

Put the bike in neutral and rev the bike to the max and see if it misses or sputters at higher revs and let us know.

My bike is suffering the same problem since a long time and one mech told me it was the coil.The symptoms are similar with both carb and electrical issues.So in spite of ZEN guys telling me that it's a carb issue and nothing to do with coil or electrical .I went ahead and got the whole electrical system checked by auto electrical pro and the electricals are fine.

Solving carb prob is very difficult,especially in CV carbs.The more the complications ,more complex the problem detection.

That's why i have told you guys not to play around with the carb ,it's a damn fragile and costly affair,if things go wrong.

@chief ashman

I even got the carb tuned with a co machine and the problem is still there and the TVS service center where i got the carb tuned are saying carb is scrap case now.That's how dealers deal with things they scrap the carb and mechs cant tune the carbs properly.So now either i have to try another carb out or straight away go for a new carb.Hope you understand what i mean.

@chief ashman

Get the carb and jets cleaned as rust might have flown into the carb.

If i put the stock main jet 97.5 the sputtering goes away and any bigger jet causes the sputtering.Then to make matters worse,in spite of putting the biggest main jet 125 the plug will be light colored when ridden at highway speeds.Meaning its not running rich.But the sputtering is caused by a main jet size which is too big.Then again the plug should be dark in color if the main jet is too big ,if revved hard.If i use the stock jet of 97.5 and give it some stick on the highway,then i will end up with a seized engine .
That's the reason why carb problem diagnosis is difficult.I have personally checked the slide,diaphragm,the smaller diaphragm and the jet needle is at its richest position too.The spark plug is saying not enough fuel is coming at higher revs, but the symptoms indicate that the main jet is giving too much fuel.

The mechanical aspects of the bike are fine.I've tried out different plugs,did check the fuel tank,the fuel flow,the carb's sump was checked ,the float can't be adjusted in our carbs,Tried out different things like removing a foam,then even removed the whole air filter system itself!!

Another thing,i've checked the intake manifold too.

Now the only thing left is to try out another bs26 carb and then a bs29 carb.

================================================== ==

Gixxer bro, I did what you said this morning... the bike does not miss or sputter .... but the sound goes high and low at times. Did it again after a 7 km ride... the sound too is ok and does not tend to sputter... will do it again in the evening.

This morning when I started the bike, I saw some plumes of white smoke ... though it went away after a few seconds, and then when revved, there was a little bit of black smoke, which also went away. I hope nothing is wrong.

I guess it could be the rust from the patched-up tank in the carb. I will have to get it cleaned properly.

Any other theories are welcome.

If you get black smoke when you raise the throttle, it means you are running rich.If it is white or blueish smoke you are getting oil in the chamber.Take out the spark plug and see.....if it has dry black coating you are running rich..if it is wet black coating you have oil getting into the chamber...if it is tan color without deposits...your combustion is optimum...if the plug is white,you are running lean AFR.

================================================== =

prs bro, thanks for the answer.

I have been showing the spark plug to the mech on a regular basis and he insists the plug is fine and indicating optimum running. Well it's been more than two weeks now and I must pay him a visit sometime this week and find out the truth.
What if oil enters the chamber ... how do we go about ... or how to tackle the problem?

Post your plug pic here and experienced Xbhpian will be able to guide you,and you can learn yourself to read plugs.If Oil is coming into chamber,there are normally two ways..one is through the Valves stem seals failure,and the second is a worn bore/piston rings which allows engine oil to enter the chamber.
In the first case only top head to be removed,stem seals replaced and engine will be ok.In the second case the engine must be opened and reboring with a new piston to be done and fixed.

OT:- For the first time I managed to ride a R15 for a few kms, The power is nothing to talk about[I am surprised that it belts 17PS], though it is quick you dont feel it, the punch just aint there, I still feel my bike can give this bike a run for its money only in a straighline. The fun factor just aint there. So where does this bike score more points than, BRAKING :- excellent brakes, amazing feedback, gear box was excellent. I could not test the handling much, the bike had just done 1200 kms, so did not want to push.

Sorry for the OT guys.

Service done&some queries

@All: I got my Fiero F2 serviced on Saturday after 3.7K kms.
The head leak issue has now been addressed&there is no more leakage.
The head gasket was changed, head decarbonized&that's about it. Paid Rs.1500 including 2 mirrors&some Iftex+polish bottles etc.
However, the cam chain has been making weird noises in the last 2-3 services. This time it should have been replaced, but the mech.didn't do it. Now I'm stuck with an overtight cam chain, resulting in sluggishness at lower speeds plus a little bit of metallic vibration at around 50kmph. After that the bike responds well though.
The mech. says we can replace the camchain next time, no need to open up the head, only the upper portion is enough.
Can anyone tell me whether this is possible?
On other counts, the head was in great condition-valves were fine so we didn't even remove the valve springs. I rubbed off the carbon from the piston head&felt very happy that the bike's engine is doing great, even at 53K kms.
Switched over to Tru4Premium 10w30 semisynth&took it to the highway after getting the carb tuned slightly to see how the bike performs. After a long time, the bike could touch 105kmph, and engine was not overheating at all. I am satisfied. Michelin tyres are beginning to show their superiority too!

Now, I have one problem which I hope somebody can throw some light upon: All electricals have been working properly except the engine kill switch, which used to have some loose contacts after rains. Battery is about 1 year old-Amaron MF type. But offlate, the bike refuses to start after a wash/standing in heavy rain. I had got the sparkplug adaptor changed, but no avail. But after an hour or so, it behaves normally.
The mech.thinks its a Magneto coil gone weak, but no way I can buy his explanation-the bike starts in a single kick even if left for 10-15 days.
Has anyone faced this? Any ideas what to check?

This is what I also felt when I got the bike-maybe it was a mistake?
Keep it in its powerband (7K-9K), and you will surely feel the punch!
The bike scores due to its Deltabox chassis, liquid cooled 4 valve engine.
Ride one at about 130kmph for 2-3 hours continuously&you will understand!

I know where all the R15 scores from this forum, my review was just from the small ride I had, also since I rode it at a relatives place, I did not have my helmet, so did not really get a chance to take it above 7, but I did manage till about 7K revvs, I am eagerly looking forward to another blast on it, this time hopefully during day time. I also liked the ride quality, soaks up the potholes pretty well.

Yes, it has a link-type rising rate monosuspension i.e., it adjusts rigidity based on the weight on the swingarm. Result-it never bottoms out.
Btw, my R15 is in Bangalore now. Need to bring it back next week.

At Joel's place for surgery?