kz 750 twin excessive vibration

Maybe there are some production differences on teh 750 twins, I didn't have any trouble at all installing the 17 tooth.

I seached the archives but couldn't find that thread, I know the giy went a "lot" higher than 17/38, and am pretty sure it was 18/34 or something like that, and he was looking for a smaller rear sprocket :woohoo:

I figure he must have weighed 100 lbs soaking wet to deal with that kind of gearing

Biquetoast, I bet you posted in that thread also, I remember there was a pretty active discussion going on

my next step is to check if the vibration continues when the throttle is let up like steell suggests. Then I am going to hook up a manometer to the carbs and see if one of the carbs does anything odd after it goes into the higher rpm range.

I will let you guys know how I turnout, thanks for all the help

how many bikes have you owned? twins shake

triumph 650 vibration in excessive
or a bonneville 750 a rider cannot keep feet on pegs at 60 mph that is vibration! 360 deg. crank design ( both pistons go up and down at the same time)

gotta think there is 2 350cc lumps shaking up and down in there with a 180 degree crank design.(one up one down) this is one way to use dynamic balance to make it twice as smooth as the 2 bikes I mentioned before (half the vib.)
I hate to say you might be chasing a ghost

if its too much sell it and get a inline 4 or a flat 6 those are smooth running engines

trippivot wrote:

how many bikes have you owned? twins shake .....
I hate to say you might be chasing a ghost...

That's kinda where I was at *until* he mentioned he gets 33mpg. That's when I started believing that there is something seriously wrong. My twins ALWAYS get over 40mpg, no matter how hard I run them, and usually between 45 and 50mpg.

A few reasons for excessive vibrations in the KZ400/750 twin engines:

1. Loose engine mounting bolts.
2. Carbs out of synch.
Also check the vacum piston diaphragms fro cracks. If one is good and the other isn't, one cylinder will get more fuel than the other and it might cause vibrations.(I'm not shure about this though, but it is well worth checking them anyways.)
3. Worn out or stretched drive chain and sprockets.
4. Worn out or excessively stretched primary chain.
5. Worn out balancer chain on the crank balancer. If the balancer chain sprocket on the crankshaft wear out, the balancer chain can "jump" a tooth (or several)on the sprocket and the counterweights gets out of timing with the crankshaft and the pistons. And the sprocket can not be replaced, so you will need to replace the crankshaft.
6. Worn crankshaft main bearings.

The issue is solved; it was the spark plug boots. It turns out spark plug boots have a resister inside of them, when the resister goes bad the resistance value goes extremely high like an open circuit.

For some reason it was able to idle and run fine at lower rpm, but when it went higher the bad resistor caused the engine to misfire, ie not a good or consistent spark. I am not completely sure of the theory behind it, and why the resistor is in the circuit, either series or parallel, but that was the problem.

I replaced the boots and wires after I ohmed it out and discovered this, and it ran very smooth.

Thanks for the help, the tip about checking if there is vibration on acceleration as well as deceleration help to pinpoint the area of the problem.

I was wondering what vehicle has a 17 tooth front sprocket that would fit in place of the 16 tooth. Do you also know of a vehicle where a smaller rear sprocket like a 33 would fit the 82 750. my initial thought is another kz from the same year range, but I don't know if kawasaki kept the bolt configuration and spacing the same.

thanks for all the help, me lesson is to replace the cheapest, easiest parts first when there is a problem.

ndali wrote:

The issue is solved; it was the spark plug boots.

Yay!
Boy, I was close, zooming in on the coil, thinking one cyl. No cigar though.
Glad for ya!

You can change the timing by moving the iron slug relative to it's mounting arbor on the advancer. It would be guess work and not very convenient to do because you can't adjust it while the motor is running.

The KZ twins are remarkably smooth for twins. Everyone I know who used to ride the Honda CB twins always can't believe how smooth the KZ twins are.

If it's bad enough to seem unusual, it probably is something wrong.

I took the bike out on the highway yesterday and put on about 200 miles, it runs smooth. Still needs some work like replacing the handlebar isolaters but it is working great.

The bike got 45 mpg running at 5k rpm and 70 mph. I have the original 16/38 configuration. I was hoping to get around 55 mpg on the highway, was wondering how your bike performs and what specs you have on it.