I reckon your problem is jetting - too lean, probably.

Try raising the needles one notch at a time and make sure the main jets are clean and your air filters are clean. Do a plug chop after each change of needle height or jets at the relevant throttle position and check the plugs.

Just on a statistical basis, carb problems are far more frequent that cam chains jumping teeth on sprockets.... just sayin'...

Thanks, one more: by plug chop, you exactly mean?

Pilot jet controls fuel flow tickover-one quarter throttle.

Needle position 1/4-3/4 throttle approx.

Main jet 3/4-full throttle.

Run bike on 1-2 mile stretch at appropriate throttle opening and check spark plugs to assess mixture; should be light tan colour, not white (too lean) or black (too rick). Adjust needle position +/- jets accordingly.

I would suggest putting everything back to standard factory including the air filter and start from there; you will likely not have to do anything further.

What about neddle in second carb? Should be in the the same position as the main carb?

An odd thing: I took out the spark plug and is totally with black powder....??? What does this tell me??

Mixture it too rich or you are burning oil or you have the wrong type of spark plug in there, or possibly a mixture of all three.

What is the compression (valve clearances must be in speck) and beware automatic compression release if your bike has it?

I would imagine so, but I am not an expert or even very knowledgeable about dual carb set ups where there are two carbs for one cylinder.

I`m happy to report that I finally managed to solve the problem posted here.

Although, a new one came up; and I`m sure it also has to do with the carb. The bike is starting properly, it keeps at idle as it should (1200 plus revs) at full throttle just fine. Now, the little mishap is that at a sudden stop it goes off, even when pressing the clutch correctly. If I stop slowly, there is no problem at all. Or if I stop suddenly but give a couple of throttle it keeps at idle as normal.

What can I check or do about it?

I will still stick by a loose chain being a problem, but I have since found mine was caused by something totally different, I still changed the chains and tensioners

My problem is here

Cheers
TS

So what was the problem in the end? Did resetting the carbs/jets/needle heights solve it?

Your new problem sounds like your clutch is not disengaging completely - needs adjusting.

The problem was the position of the needles; I adjusted them and and that was fine.

Now, the current minor problem is happening even when I just move the bike forward and use the brakes with a sudden stop not even engaging any gear.

OK, good. If the cam chain is not noisy, forget about it for now.

Now adjust the clutch exactly as per the manual - I suspect this will solve your problem.

I changed the chain anyway. I think you have not read carefully or I did not express myself properly. It is not clutch related since the problem shows up even in neutral just a sudden movement makes the bike go off.

Well, funnily enough, Rich07, I do have better things to do than read every word you post on the internet.

Since my advice does not seem to be appreciated, despite the fact that following it has solved your problem to date, I'm going to refrain from further input to your issues - you can fix your own bloody bike.

Now piss off.

Not on these pages, please
 

Come on, guys! Doc, that was really uncalled-for and not suitable for the best and most helpful Yam-trailbike forum out there. Kindly do us all a favour and delete that post. For the record, I'm sure I speak for more HUBB users than just myself in that we do appreciate your (usual) input.

Rich, I don't currently see your reference to changing the chain - please be more tactful when replying to helpful riders. I don't think you meant to sound rude but short lines of text can be such a blunt instrument.