Ducati 900 MONSTER CARB – BRADS FINAL EXHAUST STORY ( A MONKEY FOR MY BACK )

Well, I could have done this the easy way a few months ago, but I just couldn’t help myself. I got a local man, Mark Harris from MADAZ EXHAUST, to put a cross over into my ARROW system to see if this was the reason for the loss of peak power. Mark was a bit concerned at first about how it would look, but my repeated use of words like quick and cheap wore him down in the end. The result was a very nice job that you wouldn’t even notice if it wasn’t pointed out.

The only problem was, the power output didn’t really change. The graph below shows before in green, after in red. Certainly extends the power curve, but no increase in peak number.

I had a feeling this may have been fuel related, so I wacked in the lambda probe for a quick check. Right again. Now I had a pretty horrible lean spot in the middle. Compare the curves below. Red is for the std headers with some good slip ons, greens is for the modified ARROW TWIN TUBE. Wow. Less power and a jetting problem. Looks like I’m on a winner huh.

So I rejetted to suit, pulling the carbs apart once again. Did I mention at this stage I really wanted to just stop working on this bike and sell it? Hmmmmm. So I ended up with the next set of curves. As you can see, the lambda curve is much better, even if the power isn’t. You can feel it on the road, though. Red is obviously rejetted. At this point I was starting to wonder if the location of my cross over was the problem. Too far down the header pipes maybe? Just enough to make me go aaaaargh.

So for a final comparison, below is what I finished up with, against what I could have had with a set of slip on mufflers and the standard header pipes. I’m sure you know which is which. Just goes to show how good the std headers work, and that I should have listened to Doug all those months ago ( the 900 SS ie that makes 90 Hp uses std headers ). A good output to for that setup, simply being slip on mufflers, cams dialled, jet kit and open airbox lid. A very enjoyable little machine.

The last graph shows final versus std. Bob the Parts King went for a spin at my request for some feedback. His verdict was smooth and strong. Pretty much what I expected. The smooth bit comes from the 35 pilot jets I fitted ( 40 std ). I have done this before to bikes with an open airbox lid, but having my own bike to play with gave me a chance to come to this setup over a period of time. This is one of the reasons I like having my own bikes to play with. I find out why I have done things in the past, and if I have ever disregarded anything I shouldn’t have. Turns out things I thought I had overlooked in the past were not important, and I was pretty much spot on. Nice when it pans out this way. This bike is very nice to ride. Almost as smooth down low as the injected version. Pulls top gear very nicely from 3,000 rpm. A combination of jetting that works very nicely indeed.

Pity I’m now selling it, but 4 is still too many. Better than the 5 it was though. For those who don’t know, the mighty KR1S went to a new home a little while back. The sale price paid for the last engine rebuild plus a little bit more. Good way to lose money, two strokes.

Anyway. I’ve learnt a few things with this one. Been right through the carbs looking for the best setup, arriving at where I had been previously, but with a better understanding of why. Kind of wish I’d stayed with the std exhaust headers, but it’s a bit late now. The high comp pistons I was hoping to go with didn’t come about either, as it got to the point where I simply had too many projects on the go and not enough time or money for them all. I have also discovered that 14/39 gearing is just that little bit too short, whereas 14/37 is just right. Does kill the great second gear wheelies a bit, but that can only do me and my licence some good.

Looks pretty good with the single muffler I think. Hopefully someone else will too. I’ll finish up with a photo.

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