QuestionI have a 95 Suzuki Katana 600. Starting about 6000 RPM, I can feel a vibration start that gets worse until about 6700 RPM then starts to go away until 7500 RPM, at which point I can't feel it anymore. It does this even when I am stopped and just rev the engine. The vibration isn't a wobbling kind of vibration like an out of balance tire. It feels more like hitting a baseball with an aluminum bat and not holding the bat tight. The vibration feels like I'm getting poked with needles. It's not just the handle bars that feel this way, but the whole bike...frame, gas cap(not so much the tank), rear seat handle bar, etc.
I'm finding it really strange that it only does it thru this specific RPM range. I've already had the carbs cleaned because one mechanic told me if they weren't synched up right it could cause vibration like this, but that didn't change it at all. Everyone else has no idea. I'm wondering if this is a sign my engine is about to crap out on me or if it could be just something loose. Any ideas? Or suggestions where to look to find the answer?
chris
AnswerGood question. Every bike/motor has its quirks and you seem to have yourself an interesting one.
The vibration you're feeling is some resonance that peaks at 6000-7500 rpm. It has to do with the rate of vibration of the spinning motor synching up with the rate of vibration of some other part of the bike. It is probably entirely within the engine, for example, your crank is slightly out of balance and one connecting rod is also slightly out of balance. They juxtapose at 6000-7500 rpm and whip each other up, then head the other way as the rpms get higher.
I don't think it's a sign that your engine is headed for motorcycle heaven. Get yourself one or two good torque wrenches, a shop manual, and spend an afternoon re-torquing every nut, bolt, and screw on the bike. (This is a good way to get better acquainted with your bike and spot other problems along the way!) I would strongly consider loosening all the engine mount bolts at once before retorquing them...personally, I would even try it when it's running at idle, though I don't necessarily recommend it to someone else.
After making sure everything is A-1 tight (you'll probably discover that something wasn't!) this might clear up your problem.
Also try using a different type of gas. If you're using 87 octane now, try a tank of 92 and see if it changes, and vice versa. The rate at which fuel burns affects the position of the powerband, and that may in turn affect where this vibra-spot is.
This, of course, is all speculation. If it were my bike I'd ignore it, or sell it. But assuming you want to try to fix the problem, or at least discover what it is, those are a few idears for ya.
Pat
