Hey folks. As I have mentioned earlier in my build thread, I've started doing a bit of drag racing with my KZ1000. My best time so far was on my first night, running a 13.078 @ 100.75 MPH, which I thought was pretty good first time out, and knowing that cylinder 2 is a bit hurt.
I went out the next week and started having issues. It would seem to launch just fine, but then suddenly bog down to nothing. I'd basically have to close the throttle and crack it again to bring it back to life. So, questions.
1. What might cause the bog off launch? My guess would be that I was launching at too high an RPM, and with such a sticky track, it was grabbing too hard and bogging the motor down?
2. With cylinder 2 hurt, I've got plans to rebuild the motor this winter. I might be able to get away with a hone and rings, but looking at maybe going big bore. Can I reliably run a 1075 Wiseco kit on the stock carbs (VM26)?
3. I'm also thinking about giving it a different cam. I pretty much daily this thing throughout the summer, so I'm not looking to overdo it, just looking for mild performance gains. I don't know a whole lot about cams so I could use an education. From what I can tell, a Webcam 118 grind would be best if I don't bore out the motor, is that correct? What cam should I look at if I do bore the motor?
Here is another Cavanaugh reference:https://www.kz-1000.net/post/130285291257/faq-about-kz900-kz1000-engines
If you upgrade to a 1075 kit, most folks go with the 10.25:1 compression as opposed to the stock-ish 9:1. In this case, I think higher compressor allows for/requires performance cams. But Larry generally seemed to recommend modest cams along with good porting (his specialty). He seemed to be a fan of the 118 grind.
As for sticking with the 26mm carbs, there is no reason they would not work. However, you might be giving up some power at the top of the RPM range as a smaller carb body can only pass so much air volume. On the other hand, smaller carbs are said to have better throttle response in the middle range than larger ones.
The place where you might run into trouble with the VM26 is if you went with a really big gnarly cam. As the cam gets more aggressive, generally the optimal power range moves to a higher RPM. A gnarly cam paired with small carbs could mean that as the RPMs climb, just when the cams start really working they get choked by the smaller carbs. So that would be bad. But it doesn't sound like that's the direction you're going.
A modest upgrade might be to find a set of VM28s from a 79/80 KZ1000. These have accelerator pumps and are not in really high demand, although prices for all of this stuff have gone up a lot recently. You might have to watch Ebay for a while before you find a good set at a reasonable price.
This is what they look like, but don't buy these because they are gross and overpriced.
Need more info, What rpm are you launching?? Is it bogging off the line? or after you leave?
I was launching right around 6500 RPM. It worked out great the first night at that RPM. It was bogging right after I'd leave with 5 - 10 feet. I was trying to find a video of it happening, but it isn't very obvious in video. From the saddle it feels like I may as well put my feet down.