Kindly check your spark consistency and intensity it may miss sometimes due to faulty coil. That is why more black and white mix in your spark plug. It was happened to me with all the symptoms like yours.

+1 to this.

What is the AFR setting, after you changed the air filter ?
change your spark plug to std one.
Check your compression for correct values....what engine/piston work was done before ? normally the problems you have described is due to either Rich AFR or lack of piston ring sealing due to wear....
Lean setting as well as rich setting of AFR will reduce top end..
Lean setting will cause engine heating and better FE
Rich setting will cause cooler engine,and lower FE.
A worn Bore/piston rings will cause , lower FE and lower speed at full throttle due to less compression and hence lower power

Please find my replies in BLUE

Engine oil flowing through back into carb or air filter is unheard of...i guess you are talking about the blow by gases coming into the air filter area...if you get high blow by then it is an indication of loss of compression due to bore/piston ring failure...merely changing the rings will give temporary relief...you may need reboring of cylinder with new piston.
how is the blow by deposit of oil in air filter area now ?

Pardon my poor knowledge. I am not too strong technically. But what I noticed was too much of engine oil in the air chamber, and even the air filter was soaked in oil. That was about 5-6 months back, and the mechanic replaced my piston head, valves and and piston rings.

After that repair, there has been no more deposit of oil in the air chamber.

I guess you are still in run in period to set your bore and new piston rings....after 500 kms check oil color through dipstick...if it had turned dark, you still have compression leak problem...

Still in run-in period? I have covered more than 3500 KMs since that job!!
After that overhaul, I let the new parts run-in properly till 1000KMs, before opening up the engine.

Moreover, this problem has surfaced only since the last 10-15 days. Earlier it was performing in it's true blood. I have taken three to four 150+ KM trips with constant 90KPH up/down without facing a single issue, that too, with a 45KPL mileage!

Since yesterday you had PM me, i had a discussion with my mechanic about all the issues.
1. Noise- The noise you have posted is tappet noise. There is nothing to worry as slight tappet noise doesn't cause any problem. Instead a tight tappet causes a lot of worry.
2. Engine - Since you have changed the clutch plates so clutch is ruled out. However you said you had changed the piston rings. Was the piston and rings changed or only the rings were changed. If the piston was changed then was the bore bored to +1 size or a new standard size piston and rings were used. Please reply to this as it is very important.If you have changed only the rings then your problem lies in the bore. Please reply to my query and i will be able to help you.
3. Firing- Is your engine mis-firing after 7000 rpm or simply refuses to rev after 7000 rpm.
4. Carburettor- since you have mentioned the carburettor was cleaned was it refitted properly. Since you mentioned your engine is not shutting even when the AFR screw is closed fully, i doubt somewhere air is leaking. Re-open the carburettor and check the slide if it is fitted properly. Refit the carburettor properly by washing with petrol and also open the AFR screw And check the condition of the o-ring in there. Also see that if any carbon is there on the pointed tip of air screw. Usually carbon deposit on air screw causes same problem as it will fail to give proper mixture to engine.
Carburettor tuning:-

There is a lot of mis conception on carb tuning here.It is not a knob such that you make it rich or lean but a well tuned carb will behave like a FI.
So before tuning the carb ensure carb is clean and fitted properly.Also the air filter is clean.
Now the procedure-
1. Turn the AFR screw 2 turns from fully tight position and set the idle at 1200 rpm.
2. Ride the bike for 15 minutes so that the engine warms up to correct temperature.
3. Now with the idle screw increase the idling to 2000 rpm on the tachometer.
4. Now with a screwdriver open the AFR screw very slowly(1/16th of a turn at a time) and give 2-3 secs for engine to respond.
5. Always look at the tachometer and keep on opening the screw slowly.
6. At a particular point of the AFR screw the RPM will be highest i.e the reading on tachometer will be highest.
7. Now slowly turn the AFR screw to either direction from the point where the idle is highest. You will see the idle will decrease from the highest point.
8. Leave the AFR screw where the idle is highest and decrease the idling by Idle screw to 1100 rpm.
This is your ideal mix.
There is no rule that your mixture setting screw will be at 4 turns or so. If it was so easy then there will be no requirement of retuning.
Follow the above procedure.
I am thinking of DIY thread on carburettor tuning in XBHP with video on how to properly set a carburettor.
In splendor the AFR needs to be opened 3 turns but in my joy it requires only 1.25 turns. So the thing is that the screw is there to adjust according to needs of engine and not just turn it 4 turns because some other bikes of same make has 4 turns.
Since your bike is not revving beyond 7000 rpm i am sure that your bike is loosing power. Please respond to my engine query and re-tune the carb by my above procedure.
5. Timing- since the head was opened then was the timing properly set. Since even one teeth of timing sprocket if mis-matched will cause a great headache. Also i would like to mention that a if the timing is not perfect then a variation in AFR screw will not cause much effect. But if the timing is perfect then a slight deviation of AFR screw from ideal position will create havoc.
So now your work is to check the timing, Check the carb and tune it as suggested, report whether the engine is mis firing at 7000 rpm and report about the work done in engine- was the rings changed, or was the piston with rings changed, if piston with rings changed was std. size piston used or bore was bored out and oversize piston was used.
Post the above query and i will help you.

Dear Sibun,

Please find my replies in blue above.

As per your carb-tuning guide posted above (and a very similar technique posted on xBHP as well as on another biking forum), my ideal AFR would be around 4.75 turns CCW. However, being a Yamaha, fuel consumption at the optimal AFR is too high for a 125cc (35-38KPL city under optimum AFR tuning). That was the reason I had de-tuned it to a leaner mix.

Now I am having a concern regarding the timing - since you have mentioned that if the timing is not proper, variations in AFR won't make too much of a difference and if the timing is properly set, even a small adjustment in AFR will cause a dramatic change in performance.

Yesterday I spent another evening with my mechanic and blasted him left-and-right for not doing a proper job and demanded my money back.

After that blasting, he opened the engine and did some valve adjustment - the pickup seemed to improve slightly after that. The tic-tic sound also reduced to a small extent. The mileage also seems to have stabilized - now its around 40kpl reserve-to-reserve.

Rode the Glady to office today. 60 came up a bit easier than usual and I did touch 80kph@7000RPM for a second. But the 'stressed engine' feeling was very apparent and the engine was vibrating as badly as a old 100-cc bike would vibrate at 80KPH.

Hope this update helps. Is there a problem with the valves? Will a slight better adjustment help in restoring the smoothness of the engine and the previous performance? How do I check if the timing is set correctly?

for checking the timing can you please post the photos of left side of engine. then i can guide you.
regarding piston can you tell me if your engine was bored or only piston.

Will do that today evening. Do I need to open anything or just click a pic the way it is right now?

Regarding piston, only the piston head & rings were changed. Endine wasn't rebored.

Post the photo of left side of engine without opening anything and i will tell you the procedure for checking the timing.
Your post on changing of piston and rings only confirms my doubt on leaking of compression.
Your engine is leaking compression can be deduced from the following symptoms:-
1. Engine feeling strained at high rpm.
2. Engine revving in neutral but not on load
3. Optimum setting at 4.75 turn but it should come at 3-3.25 turns.
4. Engine hitting a brick wall at 7000 rpm without any mis-firing or hiccup.
5. Speed of 70 at 7000 rpm is less for 125 cc engine.
6. Mileage low, usually it should be between 55-60 kpl in city.
7. You changed the piston and rings, what about bore as the bore will be worn and leaking compression.
But first check the timing and then check bore.

got ur PM, sorry for replying late as i was not well for last 3 days.

read the entire thread.

first of all, i suggest that you dont do anything yourself as it seems you lack the skills required. plz dont mind, i may be blunt, but thats true.
next get a good mechanic, otherwise go to ASC.

now.coming to your problem-
# your exhaust seems to be ok, unless you have not messed around with that too.... just like carb and filter.
# replace ngk spark plugs and put brand new stock spark plugs. psr already suggested it. have you done it ?
# get ur carb cleaned thouroughly and get it tuned by a yamaha asc or a good mechanic.
# check engine oil level and make sure the oil you are using is for bikes only. god knows what oils you have been using .... coz i never heard wruth. remember it should be mentioned on oil can that oil is only for bikes. make sure your current oil is for two wheelers only and not for-" petrol four stroke engines- bikes and cars".
# i think now you have replaced your air filter with a new stock paper type filter. good.
#clutch plates also replaced. good.
# now tell me, what is the meaning of piston head as you said last time piston head and piston rings were replaced.
# piston is never replaced alone as piston and bore is a matched set. so you either replace both piston and block (cylinder) or rebore the block and put an oversize piston or dont replace any of them instead just replace piston rings as a cheap and quick fix method.
# last time when you had oil in air filter it was through breather pipe from crankcase. too much oil from breather pipe means loss of compression from bore. your mechanic was aware of this and he made a quick fix by replacing only half of the parts that actually need to be replaced (either due to you forcing him to make it cheaper or him trying to prove that he can repair it in much cheaper way than other mechanics). next when you messed up with your air filter, more dirt went into engine spoiling it further.
# so as per my view you need a block piston replacement.
# and the valve adjustment your mechanic has done- it seems to me that was just tappet adjustment.
# but still the backfire/misfire issue remains. i am not able to get a solid reason for it. i am replying from mobile so cant hear/see your video.
#also make sure there is no problem with the petrol you are using. if in doubt try filling from different petrol pump.
# also go to a good yamaha asc and get there opinion.
# above suggestions are keeping in mind that whatever is not reported is ok like tyres are stock size, air pressure is ok, etc etc.

Edit:
# plz give me the link of wurth engine oils india website.
# gulf pride 4t is API SL rated. i have very small doubt about its suitability to wet clutch bikes, but that is beyond the scope of this thread.
# your spark plug pic looks some what weird may be bcoz it is ngk, is it ngk? btw, is there oil on the threads of spark plug ? are your spark plugs tightened completely??
# i dont think there is any timing issue with your bike unless somebody has changed it . .......

WILL BE OUT OF TOWN FOR 2 DAYS - THU & FRI

@Sibun: Will update pics once I am back on Sat


Can't really comment on that since I was completely clueless about engine matters and hence, completely dependent on the mechanic. I just left the bike with him to be fixed, and I got it back a day later and was instructed to 'run in' the bike for the next 750-1000 KMs. What I had quoted here is what that mechanic had described me.



If a compression leak is confirmed, is there no other way out but to replace my bore & pistons?
Where can I get a compression test done? I tried some Auth. Yamaha Centers (Orion Motors, Koramangala and Panache, CMH Road) but those guys are playing coy. Checked a number of local service guys but nobody seems to have the right equipment. One guy just stuck his finger into the engine and declared that all was fine



Wuerth India Website: http://www.wuerth.in/web/en/website/index.php

GUlf Pride 4T PLUS (not the regular Pride 4T) is widely preferred for the Gladiator along with Motul, as per what I derived from the discussions on the Gladiator Ownership Thread and Universal Engine Oils thread on xBHP.


The posted picture belongs to the old stock spark plugs - before I changed to NGK.
As of now, I am using the old stock spark plugs.
For curiosity sake, why are NGK spark plugs not recommended? I read on a different thread on xBHP that they were the best (And I paid a bomb for them too!)

Thanks, Sibun and princesirohi