kz 750 twin excessive vibration

Nope, no adjustment on the timing, unless you slot the mounting holes for the pickup. The pickup mounts directly to the case on the twins, not on a mounting plate.

A minor correction on the rotor, none of the 750 twins I have seen have a key on the rotor, it's just a taper fit.

My thoughts are that if you slot the mag pickup, then the timing can be adjusted, but you lose the means of detecting if it is timed correctly.

When I looked at my timing, it was off by about 3 degrees at idle and 4k rpm. is it worth the effort of shimming it or some other rigged up method of adjusting for the extra precision. I don't have enough experience to know how significant of a difference that would make on overall engine perfomance.

steell wrote:

Nope, no adjustment on the timing, unless you slot the mounting holes for the pickup. The pickup mounts directly to the case on the twins, not on a mounting plate.

OK....Wierd but OK..

A minor correction on the rotor, none of the 750 twins I have seen have a key on the rotor, it's just a taper fit.

So.... If some schmoe were to fiddle with the rotor bolt(I'm assuming it is held by a bolt) they could wack the timing by turning the rotor? Say by trying to turn the engine over using the rotor bolt? It's hot and I'm proberbly denser than usual. My usual density is that of carbonium or upsidasium!:silly:

I took a look at the rotor and it is bolted on tight.

My next thought is to look at the coil, I am wondering if I have a weak spark and the coil can't keep up at high rpms therefore it is missing.

I am just checking everything I can think of now.

Steell, it looks like you have a kz 750m, what are your thoughts about the bike itself, is yours smooth above 4k?

I don't have a KZ750M1 CSR at the moment, I sold it last year because I hated the riding position, currently I have a 1980 KZ750G1 twin. The rotor I was talking about is the alternator rotor, that was in reference to it coming loose and wobbling, thus causing the vibration. The timing advancer fits over a pin on the crank and is not adjustable without a lot of work.

I have checked three 750 motors by using a dial indicator to find TDC, and every one was ~ 3 degrees retarded on the timing advancer.

You can use a rat tail file to elongate the pickup mounting holes and gain a little adjustment that way.

I had a KZ1000 CSR, and one of the things that bothered me about that bike (aside from the riding position) was the high frequency vibration, but I have had no problems with any vibration on the 750 twin. I know it does vibrate a little, but not enough to get my attention, as in I don't really notice it.

But I spent a lot of time in my youth riding BSA, Triumph. Arial, Matchless, and Norton twins, in addition to a few BSA 441 Victors. At 4000 rpm a BSA 441 Victor defines vibration

Where are you feeling the vibration? Hands/feet/seat? Both the footpegs and the handlebars are rubber mounted, and the seat has padding, so where is it coming from?

BTW, I think the 750 twins are more relaxing at 65-75 mph running 17/38 sprockets instead of the stock 16/38 sprockets.

Oooooh. I'll have to try the 17/38 sprockets.:woohoo:
Do you loose any low end torque? Does that mean you'll be running higher revs at 55 than the 16/38 config?

Means you loose a little take off "oomph" but lowers your cruising rpm. I liked the 17/38 but my brother likes the 16/38, he had trouble taking off from a stop, I didn't, but I have lots more experience.

More of a pain taking off from an uphill stop two up, but then that's never fun is it?

Post edited by: steell, at: 2006/07/18 22:01

Thanks.

steell wrote:

...Where are you feeling the vibration? Hands/feet/seat?...

BTW, I think the 750 twins are more relaxing at 65-75 mph running 17/38 sprockets instead of the stock 16/38 sprockets.

I just wanted to add acouple things to these two points above...

I have noticed a definate difference between my two bikes -- one has stock bars (temporarily) and the other has cheap superbike bars -- in the vibrations at the bars. For quality reasons, I'm sure, the the stock bars vibrate/buzz less. Not enought to make me not get rid of them though!

Also, I had a 16/38 on the second bike... for a few days. It sucks. I've had 17/38 on my first 750 just about since I got it, and prefer it hands-down. The bike has plenty enough of power for the sprocket change, though admittedly I don't ride two-up like Steell. Go ahead, scrape a few thousand RPMs off your cruising speed....



Post edited by: Biquetoast, at: 2006/07/19 09:22

I thought about changing the gear ratios of the bike, crunching some numbers and assuming 87% driveline efficiency I calculate the following

engine sprocket: 16, speed: 70 mph, rpm: 4650
engine sprocket: 17, speed: 70mph, rpm: 4400
wheel sprocket: 33, speed: 70 mph, rpm: 4050

is there enough room for a larger engine sprocket? I looked into a smaller wheel sprocket for that concern. I noticed that other similar kawasaki bikes have a 33 wheel sprocket, I am not sure if it would fit. Another concern I would have is very poor startup in 1st gear with a 33.

I also just went through my 3rd tank of gas and am getting 33 mpg city driving. I expect that to be closer to 50 mpg, what is the fuel consumption some other owners have. I am hoping this is an indication of the vibration problem.

I agree with steell about the foot pegs, which is why I alread moved them and the controls to the front of the bike so I can stretch my legs out. As for the vibration it is worse in the arms, second by legs, and I also feel it through my body and the seat pretty bad. The bad vibration was there before the footpegs were moved, with the original configuration.

for anyone who wants to play with gear ratios I have attached an excel spreadsheet that I made for the calculations.

Stock is 16/38, at least two of us here in this thread have run 17/38, and IIRC, there is another guy with a 750 twin that ran 18/34 or maybe even 18/32 (there is a thread in the archives about it). 18 is the largest sprocket that will fit on the front, but I think 18 would be a PITA for me as I weigh 240 lbs.

The 750 twin has dual balance shafts in the motor to cancel out most of the vibration, if it's vibrating that badly then something is wrong. If it vibrates the same when you give it gas as it does when you close the throttle then it's a mechanical problem, if it vibrates worse accellerating than it does decellerating, then it's a tuning problem such as valve clearance/carbs/ignition.

I can't imagine how an 18 would fit up front. Certainly not with the original chain cover/shroud thingy - you know, that stip of metal that goes around the chain/sprocket. I had to perfectly smooth mine out to get the 17 to fit there with almost no clearance...

...and yeah, I'd be concerned if I was only getting 33 mpg. That's a little more than about half what I get...

Ok, maybe a failed coil, and you're running on one cyl? Did we discuss this already? Sorry, I'm losing track...