Hi Santtu,
the Bulldog here in Germany has to comply with all the environmental Laws and has therefore lost a lot of its original power.
As the Bulldog is not the most popular bike on the Planet (thanks God !!) there are only very few Companies trying to improve this.
To tell you the truth, I haven´t got a clue what is included in the Topham Kit...but for 95€ it can´t be much (I think it is only new jets for the carburettors)
As everybody here knows, I´m a big fan of the work Yamaha Krause in Dortmund - 0049 231 31999 - delivers (no, I don´t get a salary from them

) and it´s not due to the fact that their garage is only 60 km´s from where I live.
I just like good workmanship and technical expertise - he fabricates most of the parts in his shop - and he proves it by putting every bike he modified on the in-house dynamometer ! So there is no * around and you get a before-after curve on paper.
What do they do ?? (By the way, quite a few of these changes can be made by you..)
When you lift the Tank - you don´t have to take it off all the way..there is a hinge in the back - you´ll see the first thing you can throw away : the plastic air-filter cover (with the two little snorkels pointing backwards.) Krause makes a aluminum plate with a big venturi opening so this improves "breathing" considerably. Oh, and by the way, don´t let anybody tell you, that K&N Filters increase power..: it´s definitely not so..on the dyno we had an increase of barely 0,2 hp..ridiculous.
Now you should adress the carburettors..take off the covers and throw away the plasic "stops" on top of the slides.
Now if you turn the throttle, the slides open all the way

This would not suffice to cope with all the air it is getting..: you have to rejet the carburettors. (Krause provides the correct jet size) If after this change the engine runs too "fat" try lowering the needle by putting the clip one groove higher.
Now comes the difficult part.
The exhaust on the Bulldog is extremely restrictive. All the changes you´ve made this far would be in vain if you don´t remedy this. Krause makes a new endcap for the mufflers (look at my album)so you would have to cut off the existing one and substitute it for the one Krause provides...This is best made in a mechanical shop with facilities to weld V2A steel.
Or you buy a pair of slip-on mufflers from accessories-companies like BOS..its by far the best sounding (you´ll be really surprised

) it is legal and the change is made in max. half an hour.
Now have fun modifying your Bulldog and let us know the results.
Greets from the Axman
p.s.: please get rid of your standard handlebars..they are not made for humans !!