You are lugging the engine . With throttle closed it isn't getting enough fuel to maintain rpm necessary at the speed for the gear u are using . Raise throttle to keep the rpm above where the noise occurs . If doing that also increases speed to more than what you require right then , downshift to lower gear . This is normal for all bikes , no problem .
To move on inertia only , use full clutch or shift to neutral .

Doh , it's the recommended procedure(starting the engine page) written in the owners manual .

no its not the one you are talking about, even at lower gear with normal speed im getting ,i guess it is chain set making that

thanks my friend. i think today is holiday and you have time to explain what i need to tell them. I need to talk to them that i know every single bit of the problem otherwise they will fool me again. all my friends own pulsar and unicorns, only me own CBZ ( My baby). Now they are joking because of the vibrations and not smooth sound , low milage etc etc.
Now remember when i went there for 2nd service a guy was waiting for his bike. He also own cbz new model and his bike done only 2500kms. He said he noticed his engine sound has changed and the svc guys says its normal. but his friend who is a mach enginering student or passedout dnt knw buy he knw about engine and told him that pistion or crank i dont remember anyway that was gone he again came to SVC and told about vibration and the SVC guys said its normal no problem just valve adjust needed. then he told them that this was the complaint and if you dont know about this he will contact regn offc. then again they started the bike and said " yes we think there is a little bit sound" and finally they replaced in warranty but took about 2 weeks. so i also need to know what the problems a little briefly so that i can talk to them and convince them.

Ok, no problem. This is a common problem. The actual tuning will be the rpm will go up till a point be it 2k or 3k, it doesn't matter but after a point where the rpm will be high more turning out the screw will decrease the rpm. If your air screw is not working after a particular point then the defect is in the o-ring of air screw, either it will be out of shape or cut.
Buy a new air screw. If you cannot get a new air screw of extreme, then just buy pleasure, splendor air screw and use the o-ring with your old air screw.
A typical image of air screw, this is not your cbz air screw but it is an example:-

The black o-ring is cut and so your RPM is not decreasing.
See the placement of o-ring, first is spring, then the washer and then o-ring.
@ATHUL- You had also asked for the air screw diagram.
While taking out the air screw if o-ring doesn't come out or the washer also doesn't come out then see through the hole of air screw with a torch and it will be stuck in. With a thin wire make a hook and pull out.
There is a lot of difference in carburettor tuning. Most A**holes in Service center screw the tuning. A properly tuned carburettor will behave as a fuel injection. No matter how perfect is your engine mismatch of tuning will cause a lot of problem and also screw the engine.
Carburettor tuning is an art rather than science. It depend on experience rather then knowledge. My mechanic and I can just tell the tuning by just cranking the engine. My mechanic will just tune the bike at idle without raising the rpm and it will be perfect. So, i am imparting knowledge to my biking brothers so that they can do most of the works without depending on mechanic.
I have a very bad habit of keeping my bikes in perfect condition. Those who ride my bikes tell that it feels better than new bikes. For this habit i have got lots of scolding from my family but at last they thought it is no use scolding him.
Actually, i forgot about it.
If your friends are commenting about your cbz then i think they must ride my cbz then after that they will never comment.
First lodge a complaint against that service center to hero. I think they are selling bikes after using them as test ride bikes.
In orissa there is no complaints of any hero honda bikes with crank noise. Only two shine was there with crank noise but the bikes were replaced as from showroom itself the noise was caught.
Ok, go with as much knowledge as possible so that service center do not make a fool of you.

The above is a CBZ crank and the circled portion is the crank pin.Your crank pin has worn as a result as the crank is rotating your con rod is hammering on the crank pin and creating noise.

Here is a photo of con-rod and crank pin and bearing that is fitted to crank as in above picture.
The pin has a hole for passing of engine oil to the crank roller bearings. Usually if their is play between crank bearings and crank pin you can hear noise.

This a CRF crank but it will be almost similar to yours. the blue circle is the big end which houses the crank pin and bearing as in above photo. The dunction of crank pin is to hold the con rod and the crank, hold the two webs of crank together in balance, and provide oil to crank big end bearing.
So you can imagine how tightly the pin must be fit. If there is slight loose in pin, then the con rod will vibrate, and crank will loose balance.
Now its functioning:-
From the above picture you can see the piston is connected to con rod. When the engine fires the air fuel mixture the mixture explodes which pushes the piston down in vertical manner. Now this vertical motion is converted to rotary motion by the crank. The big end bearing and the crank pin ensure that the linear motion is converted into rotary motion of crank.
But if there is play in the pin or bearing then the crank will vibrate due to the huge force on piston.
So, since your bike is having this problem from long time then your bore will be worn as your piston will be vibrating in bore. Thank god that your engine has not seized. Even if they do not change bore by giving any excuse then after 3-4 months you will be forced to change bore so force them to do so.

Now when the crank is rotated by the piston the left end marked by the maroon circle goes out to the magneto. There is a woodruff key on which the magnet is placed. The gear which you see is the sprocket for timing chain.
On the right end marked by yellow circle it goes out to the clutch side on which the GPT(gear primary teeth) is mounted and the centrifugal filter is mounted. This gpt is linked to the clutch housing which is mounted on the gear shaft. The gear shaft has five gears and is linked to the counter shaft which again has five gear. there is a clutch dog which is connected to gear lever by a gear shaft which engages gear by moving the gears on counter and main gear shaft. You can see the counter shaft exiting out of the engine as the shaft on which the front sprocket is mounted.

So the engine operates by:-
1. The air fuel mixture is fired which pushes the piston down,
2. The con-rod imparts the linear motion to the crank which converts into rotary motion,
3. On the left side the crank rotates the timing chain which open the valves and and also the magnet is mounted which provides current to all operation in bike,
4. On the right side the centrifugal filter is mounted, and the gpt which rotates with crank
5. The gpt is linked with the clutch housing which is mounted on the gear shaft. The clutch bell is bigger than gpt and you can see in manual it being mentioned as primary reduction,
6. Then this main gear shaft is linked to counter gear shaft and both have five gears. The clutch dog engages appropriate gears as we want. This relation between main shaft and counter gear is mentioned as gear ratios in manual
7. The counter gear shaft comes out of engine and the front sprocket is mounted on it. The front sprocket is connected to rear sprocket by chain and you can see it as final reduction in manual.
This is the mechanism which drives our bike. So you can imagine how much load is their on that pin and roller bearing. So a slight clearance in them will cause loud noise like hammering.

Demand for replacement of crank and bore kit.

@ashwin.terminator: Thanks a lot for your reply. Got my reply, have changed the engine oil at 650km when the first service was done . So its time to change the engine oil again.

Completion of 20k report/review

The fs oil stayed for 3500km. From 3000 it started to deteriorate so changed it today . This time to Shell AX-7 SS.From 19k sewing machine type sound is coming, but mileage is same near 60 . Handle bar vib has increased a bit.Other thing is bike's top speed has come down. I had done 117 on this bike when ODO was 1k.Now with great difficulty it reaches 100 and Max out at 105. This week Going back to Bangalore and from there to Solapur.After that Engine work will be Done at 24 k.

If you are suspecting that , it's easily eliminated . Open the bottom chain cover and lube the chain with 90 gear-oil(with a toothbrush) and then apply some grease on it too . Take the bike to any mechanic (or even an tyrewallah) and ask him to adjust the chain slack . Correct slack is about 1.5 inches at the central part of it . It's normal for a new chain to get slack a bit quick .

So to remove the fuel screw i just keep on rotating anti clockwise and it will come out then i replace the o-ring and screw it back in right sibun

yes, absolutely right.

Sibun ji the ASC people dont like me that much as i have complained them to HERO directly and now they recognize me from a mile away....so if they dont give me the air screw can i go to any local auto spare shop and get a fake or will it damage the carb in any way ?

Outside shop also stock original air screw. If CBZ is not available then get splendors and you know they are easily available. Just use the o-ring with your old air screw. But be sure to pull out the old o-ring if it is stuck in the air screw hole.

Got the splendor air screw from outside and thank god the air screw came out without getting stuck but it looked diff. than the one you posted fro reference :



the right one is from my CBZ and the left one i got from a shop ...the O-RING is of diff. size.

the tuning has all gone bad compared to the earlier one set by the head mech see this :



thisis the RPM problem i am talking about it refuses to rise any further :

P1010829 - YouTube

wish i had a digital tacho

No, i am not talking about the o-ring on the screw head. But there is also an o-ring near the tip as in the splendor air screw. They are of same size. Where is your washer. Both of these will be in the hole from where you removed the air screw. If there is no washer then the o-ring will get damaged.
There are two o-ring in cbz air screw. One is on the head and other is on the tip. The tip one is similar to the splendor air screw. Use the washer below the spring otherwise the o-ring will be torn.The head one doesn't gets damaged so easily.You can see the o-ring in your screw to be okay. Peep in the air screw hole and you will see the washer and o-ring. Pull them out.

Ok sibun ji now i understand will peep through the hole and report back by tomorrow...dont know how i am going to remove the washer and the o ring from that tiny hole but will try .

I have one more question : is it possible to tune the carb in this condition using digital tacho as the RPM needle is stuck in place due to the O ring damage ?
the reason i ask is how come the mech at SC tuned my carb in this condition ? i want to know if its possible to tune the carb with digital tacho even with a damaged o ring like mine

i adjusted the chain sag.but i need to lube it