Carb slide getting stuck will restrict the RPM 4 K to 5 K in 5th gear..ie., 60 to 70 Kmph speed..and you have said restriction is at 2 K RPM.which is why I suggested CDI connector check up.
Have you checked proper fixing and functioning of the Choke ?
Since you are not sure what had been tampered with and how, here is a method to go about ..
1. Apply WD40/Zorrick on the AFR screw and wait for 15 minutes.
2. GENTLY turn the AFR screw CLOCKWISE till it stops.
3. Now turn it ANTI CLOCKWISE by 3 full turns(360 degrees).
4. Start the engine, with choke on for 10 seconds ..Adjust idling to 1,200 RPM in cold condition.
5. After 3 minutes of idling Raise throttle to see if RPM goes up...or engine switch off.
6. If bike switches off, keep the carb bowl drain tube in a 500 ml transparent pet bottle, and loosen the drain screw..Observe as the petrol flows into the bottle..drain 500ml and see the flow rate,and if there are any impurities in petrol..
7. If the bike starts and revs normally then go for a spin and see if the RPM is able to rise above 5 K on a clear stretch of road without traffic ,and wear a helmet.
Post back your observations

Sir, the choke lever is jam since about last two services, I forgot to mention this thing to the SVC guy and it is still jammed in OFF position. And the problem started with engine not going beyond 4-5 k rpm, then my bro tried to push it till where it can go and he took the bike till 90 kph I think at that time engine was running rich .. ? Am I right?
So then I took back my bike, and rode it below 3k rpm and came home and then after a few hours started the engine then it refused to go beyond 2k rpm! I checked the spark plug yesterday, and it was BLACK!! (It is already some 17.xx kms old).
And now I'm going to perform those steps mentioned by you.

Update

I loosened the drain screw, let the carb petrol come out on the floor and what I found was:
the petrol that was spread on the floor was not getting dry immediately, which does if the petrol is quite pure(earlier cases)...does that mean that last refill was most probably an adulterated fuel? If yes, I'm shocked because it was a really big fuel station "HP" on the Kol-Durgapur NH2.
Screwed it back and went for a small ride, now engine crossing the 2k rpm but the range of rpm restriction is increased. Engine again not going beyond 5k rpm and during that course also, the acceleration is sluggish!

P.S. A pic indicating various screws of the carb in a Karizma will be helpful.

Why let petrol drain to the floor ? if you had caught the petrol in a transparent bottle you can see by the color if it is adulterated or not....a Red color is pure petrol while a yellowish tinge is due to Diesel /Kerosene adulteration.engine not accelerating beyond 5 K RPM may be due to adulterated petrol or throttle slide stuck.
If your bike is in warranty get the carb replaced,do not tamper with it, if not ,....remove the right side(kicker side) cover,and loosen the ring on the rubber hose from the air filter ,.on the carb inlet..push the rubber hose to one side and you can see the slide...put your fore finger and check if the slide is stuck...if it is then GENTLY push it up and it will get released and your bike will be normal..
The RED marked screw should be loosened to release the rubber hose to move it aside...


Once you move the rubber hose aside you will see the slide in the carb like this..

place your forefinger under the slide and lift it..this will remove jamming and bike will be ok...

How much the front shocker dust boot costs(not the oil seal)?

There is still crazy back fires. Is it bad when the engine backfires like that.
I remember him saying that this is with the tuning and once he gets the new carb it should solve the problem.

Is there a possibility of water inside the fuel tank?. Also check that too.

Yes, it is under warranty. Tomorrow I'm going to the SVC, again bunking the college! What steps to be taken in order to claim a new carb under warranty? Should I remove the horns that I installed? Anything else?
Today, met a guy owning Karizma R(old), he asked me to check the timing chain.

UPDATE: I can redline the engine in Neutral, but not in any gear! Max 5+ k rpms.
I wish I could do this what you've explained in the pic, but the right side panel's screw is not getting turned anticlockwise whatever amount of torque I'm applying to the Screw-driver doesn't matter!

Me too doubt about it. But it is not possible, although I've run many times in rain but never allowed water to enter the tank.

@PSR Sir,
Regarding sunny's case.

Sir, I have a doubt,
wont the RPM fluctuate or something if the cause of the problem was carb/engine related. Recently saw a post from a guy who inserted a non-compatible sparkplug and his bike only revved to 6K constant. So doesnt that mean, constant/specific restrictions(like in sunny's case its 2k/5k) means the probs electrical.???

@Sunny
If under warranty then get everything replaced asap, starting from the carb to the CDI, cause as far as my experience tell's me, the SVC will go around replacing many things before actually sorting out the problem at hand i.e in short you'll get alot of free replacements.

And does you'r bike just stop revving after 5k or does it shut off???

Depending on the problem only the diagnosis can be made...
Failure to go over 5 K RPM in ZMA can be attributed to only 2 possibilities..1. is the Throttle slide getting stuck..me and many ZMA owners had experienced it..2. CDI loose contact..it can reduce RPM to 2 K to 5 K.
What distinguishes the difference between the two problem is, throttle slide stuck will allow you to accelerate till 5 K RPM on 5th gear but will not switch off the engine..The CDI problem will cut off the engine beyond 2 K or 3 K RPM.
which was the non compatible plug inserted into ZMA ? which aspect of plug was non compatible ?

135 Main Jet for ZMA available for 250rs + Shipping from Pune.

Yes Sir, exactly. You said it as it is!
The engine doesn't halt/shut down after 5k rpm in 5th gear, but beyond 5k rpm if I twist the throttle completely then also it wont go past 85-90kph and it feels like "something" is missing.

@Aneesh bro, do you mean that claiming warranty is that easy? Do I need to convince that guy about the problem first or directly ask for a replacement under warranty?


Update: Woke up at 8:15 AM so couldn't go to the SVC, will go tomorrow

Sounds more like throttle slide stuck....
Point out the problem and ask them to solve it permanently.... most SVC mechs are not good at diagnosing or correction of problem,but only at water wash,and change of oil.
But do register a complaint, and if not solved write to HM and make their life miserable...most important create records to show you have problems and you have recorded it with SVC..

Thanks sir, Didnt know about the cutting off part,info added to my database.

Its from an old post, it was'nt a ZMA, the bike was a Unicorn/CBZ-X(Sorry dont exactly remember.) the reason the owner swapped the plug was cause the NGK Iridium models were'nt available for the bike. I went through that particular post a few months back when I was re-searching on Spark Plugs to find out which model of Iridium was compatible for ZMA.

Will complete 500Kms any moment, so bought 900ML 10W30 High Poorformance Engine Oil from Hero Honda. for 200/-.




The reason I opted for this was cause during my previous run-in I noted that the 20W40(Gulf Pride 4T) kinda paused the run-in process. There was no difference with the bikes engine when I shifted from 150Kms to 500Kms(1st Service) and only when the SVC guys poured back the usual I started experiencing changes to my engine as I rode on.

Alright Sir, Thank you very much for those replies and all the infos and links. I don't know about my basics, but I have read "Carburetors" on wikipedia last evening when you scolded me to get my basics right. Next time onwards, I'll try to sound less stupid. I would have rode my bike straight to Chennai to you to inspect the problem; that much I trust you and other fellow riders here(specially on this thread), if petrol were below Rs 30 a litre or some company would have funded/sponsored the ride

This problem once solved then I'll get into the horn thing! And, I've to check that Motul 3000 4T plus also, many are waiting for reviews here

P.S. : sorry, in the last post, I wrote "Aneesh" instead of "Ashwin".. Sorry bro, hope you don't mind. You both can answer.