I am glad to have found this forum. Long story short, up until now I have only rode single cylinder enduro bikes, from 350cc up to 650cc, also some retro oldschool two stroke single cylinders like the Simson. So most of my riding up until now has been off road/ hard enduro style. I wanted to try out something different and I have always liked the classic looking naked bikes. I didn't want a bike that is very powerful, because of my lack of tarmack riding experience. One day I stumbled upon a XJ900 and though it was awsome. I looked up the different models and recently found a 1996 XJ600N which in the end I bought. It met all my criteria. It had that classic look, simple aircooled engine with enough power and I said to my self that's my bike! After buying her I had to do the usual mainteinance, engine oil and filter change ( I went with Bardahls 15W-50 synt oil), air filter change and brake fluid flush. The fuel tank was rusted inside because she sat with a 1/3 full tank for quite a while. So I had to clean that out too. Used rust converter in the end to eliminate the remaining rust. The engine with its 4 cylinders is really smooth, and I was plesantly surprised by that.
The only problem I found with the bike is this. She starts right away, pulls very nicely and smoothly even from low rpms and cruises nicely around 100-120 kmh/h.. BUT I did a test drive on a closed track to see how much km/h I would reach max. In 1st 2nd and 3rd she pulled up to redline very well, but in 4th gear I could only get her up to around 8000 rpm and 140 km/h. She wouldnt pull pass that, I upshifted to 5th and then to 6th and tryied to pass the 140km/h mark, but with no luck. It's like she looses power bogs down a litle bit, then gets going again ( this at WOT). If I ease the throtle a litle bit she starts to pull once again, but doesnt have enough power. I though that there was not enough fuel going to the carbs at high loads, but the spark plugs were black
. The carbs fuel screws were turned 2.5 turns out ( factory 2 turns), I backed them up to lean out the fuel mixture, to 1.5 turns out, and now she sounds and drives better, but still can't pass the 140km/h limit in neither 4th 5th or 6th gear. ( In 1st 2nd and 3rd pulls to redline no problem). I didnt find a similar problem in the forum and I am hoping for some help here. I am asuming assuming that not enough fuel is going in at high loads, could this be a float level problem?!
Fuel filter is clean, I didnt found any cracks in the fuel or vaccume hoses. Bike has 31K kilometers on the clock.