ZXR400L1 running bad after maintenance

[Stijnzxr400]

Hello everyone,

I am having some troubles with my 1991 Zxr400. Bike was running great, until last weekend when I did some maintenance. Chanced spark plugs, oil and oil filter and sycronised carbs. At first everything was all good and bike was running great. Now I suddenly having problems that the bike is not running on all cylinders all the time. I am almost certain it is ignition related. The first thing I did was check all the wiring that seems al good, then I swapped the old plugs back in. I also checked the coil resistance both coils are 3.3 on primary and 25k on secundary, messured with wiring and caps. But it keeps running bad. The other thing I noticed is when the bike is completly cold it is running on all four, but after about 30 seconds you can hear the bike starting to run bad and I think misfiring. When riding it is mostly below 6k rpm after that you can hear and feel that the bike is running on all 4 again when on throttle, off throttle you can immidiatly hear the misfires. Bike got new battery and rectifier last september Could it be that the CDI has gone bad, or does someone have other suggestions. I hope someone can help me out. One last thing is sometimes when I start the bike it only clicks( like the battery is dead) but then after I turn the ignition off and back on it starts. This was also before I did the maintenance but seems to be a bit more often.

[Barn Owl]

From the post I’m assuming the issues remain even with the old plugs fitted… regardless I’ll add some points.

- Have you checked the spark plug gap?
- Also are plugs from a reputable buyer? Official NGK or Denso? I know there are fakes knocking about
- Plug caps fitted properly? HT leads properly fitted to coils?
- Check cleanliness and fir corrosion in the plug cap
- Do you have an ignition tester? I’m not sure what gap the spark should jump on these but you can get tester kits that basically allow you to wind out a threaded electrode to check spark intensity. Mine was ~£7 on EBay.
- Fuel pipe kinked from the tank?
- Have you definitely refitted the vacuum hoses?
- Finally I would check your battery, maybe the starter clicks as it’s not got enough poke? Perhaps the alternator is helping it enough to fire all 4 when you give it some throttle?

[Barn Owl]

I just realised this post is quite old. I hope you got it sorted!