TOPIC:

I'm working (still) on the 1978 KZ650 SR I have. Today I replaced the spark plus with slightly hotter ones (B6ES) and replaced the spark plug connectors. The bike started right up, without even using the choke (it's warmer today than usual). I took the bike for a quick ride and it loses power at about 4K and then gets it back at about 5K. I suspect the ignition system is causing this trouble. I put a timing light, revved up the bike and noticed the timing light flickers at the same time I hear the motor misbehaving on three of four cylinders. I took a look at the timing with a light and #1 and #4 are right on the mark at idle and they seem to advance OK. #2 and #3 are a different story. When the bike is at idle, the timing marks on the advancer unit jump around the mark on the case. When I roll on the the throttle, the advancer moves as it should but doesn't quite put the two advance marks in the right spot. It stops short of the timing mark on the case. I can't rotate the points mounting plate any further and just moving the points for #2 and #3 has an effect but the advancer marks are never steady. The really funny thing is that #3 is the one cylinder that never misses a beat at 4000 RPM! Any ideas about what's causing those symptoms? Thanks.

Replace the condenser for 2&3 and see if that fixes your problem.

Thanks for the idea. I didn't have a spare condenser laying around so I swapped 1&4 with 2&3. It made no difference. So I moved the points on the mounting plate to get a little more movement of the plate itself and that seemed to attenuate the movement of the advancer marks around the case timing mark just a little bit and rolling on the throttle puts the advanced marks in the right spot relative to the timing mark on the case. So I think the motor's timed as well as it's going to get. I enriched the mixture on all four carburetors a little and now the bike doesn't hesitate like it did through 4-5000 rpms. Not perfect but much better and most importantly, the bike is rideable!

markc3wa wrote:

When I roll on the the throttle, the advancer moves as it should but doesn't quite put the two advance marks in the right spot.

My KZ 750 had the same thing. The "high RPM" mark never quite got far enough to reach the mark it was supposed to align to. I just ignore it and set it correct at the idle mark.