@NANOtechnology: I strongly feel your stator coil has gone weak-get it rewound. My bike's coil has been rewound&no problems now.

My wiring as well as the switches are BRAND NEW, also my ign key is perfect, as when i do switch it on, the switch's back-light work perfectly.
Even the circuit is absolutely fine as there are NO CUTS on any of the wires..

There's NO STATOR coil in my bike, it was removed when i installed the alternator.
I did check the sparking, and its brilliant.

Then is there some problem with the alternator?

If water isn't entering the fuel tank,or there's no air leak,then it definitely sounds like a electrical problem.

TCI, IDI, spark plug, everything is brand new coupled with handsomely charged battery, perfectly working alternator.

I did check the sparking, its perfect...

What can be an electrical issue here ??

@nanotech-a series of unfortunate events,did you check the plug adapter.If possible put insulation tape to cover the ign wire and the adapter.I had similar issues in my ol victor.

1.You are saying that there's no water entering the tank.
2. You are saying that the problem happens only when it rains.So that can't be a mechanical issue.
3. You are saying that there's no air leaking into the intake or via the air filter hose.
4. The bike runs normally when it's dry,that rules out carb issue too.
5.You are saying that there's no loss in engine compression.

That leaves only electrical issues doesn't it?

Electrical issues can't be diagnosed by simply checking the spark,it might happen on load,or it might come and go.Like with water related issues of switch gear etc.

Do one thing,buy a CBZ extreme spark plug adapter,the red one i am using.It's made of rubber and it won't let in water.ZEN TVS after seeing it,are advising it to be put on the rally bikes they prepare.

what spark plug do Fiero use in stock settings ????

The total name??? (for eg:NGK CR8HSA)

NGK R CR7E

and NGK R CR7E IX Iridium one.

Very logical explanation...it's got to be Electrical, check your engine kill switch(if you have one) for water shorting,and Plug cap

Ting Tong...Ting Tong...Is anybody here ?
Knock Knock Knock Is anybody in here ?

I guess it is........

Anand is off mood since we are not discussing the 2 legged SBKs anymore I guess!
Anyway, how often is tappet adjustment/valve clearance setting necessary in Fieros? I remember the manual having something written as check&adjust every 10K kms.or something like that.
However, my mechanic feels it is a crime to touch the tappets/carburettor&as a result the bike has never seen any tuning in the last 7+ years.
Now I'm really feeling the need for it, since the performance is going down drastically, thanks to the worn out camchain too!

There is a saying never fix what is not broken..if you hear no tappet noise,and have no problem relating to carb, leave it alone......timing chain is an altogether different thing as it involves cam, and through it proper valve timing which is very important...as a thumb rule change timing chain every 40 or 50 K if it lasts that long, and even if there are no problems.
valve seat check and necessary work for reliable running is recommended every 50 K Kms..of course there are bikes with none of these done running healthily for 1,25,000 Kms...all depends on periodic maintenance, oil used and sane riding.

What are the symptoms of a worn out Camchain?

I got the head opened up at around 50K kms.
The valves were fine, no bends, no leakages etc.
The camchain was making the loose marbles noise since the last 10K kms.&every time it was silenced by adjusting the tensioner. When the head was opened up, he showed me the camchain&I noticed it was pretty worn out&shiny. Going by the 50K mark, I recommended replacing it to the mech., but he didn't wanna do it, even though the part was in stock.
As a result, as soon as he put the parts back, the clanging noise increased manifold.
He tightened the tensioner&said, "We will change the camchain next time".
The bike ran very restricted for the 1st 3-400kms., then the normal response was back albeit with the clanging&some rubbing noise.
Now I feel the initial pickup of the bike has gone down a lot&also, the carb showed lean fuel mixture, which I confirmed by posting a pic to Anand.
Moreover the bike feels very strained at speeds above 65-70kmph.
I don't deny that I'm riding roughly, coz I'm used to ripping my R15, but I remember a time when the bike used to touch 80kmph like no one's business&hardly make any sounds at that speed!
This is why I'm planning to get the bike a complete tune up, which includes the following:
1. Valve clearance check&adjust
2. Timing chain&tensioner replace
3. Carb clean&tune up on CO machine
Apart from this, the electricals have had a checkup recently, 3-4 melted sockets have been replaced&the stator coil has been rewound too.
The bike is getting better over the time, as my suspension, paint, battery, electrical issues, tyres, everything has been sorted out.
I only wish it had a bit more power i.e., can cruise at higher speeds like other Fieros.