900 Diversion miss-fire -help please

[kawasakikz1]

I bought my 1997 900 6 months ago with only 5000 miles on the clock. It had already had the carbs removed by the dealer, presumably for the miss fire that still affects it. At low rpm it backfires badly. It seems worse in the wet. I have fitted new coils. On start up cylinder 4 does not fire. I have replaced the plugs (they were sooty on all 4) and air filter. Above 3000rpm its all fine. I have heard the pollution control gear can cause these problems. Any suggestions gratefully received. I love the bike and commute 800 miles per week on it. But if I cant get to the bottom of this it will have to go.

[CD]

Looks like its not the coils etc. I dont know the symptoms of a duff igniter box. A call to Electrex might be worthwhile (o1491 682369)

Have a look at the choke plungers on each carb. If they are sticking open the bike will run rich. Otherwise clean out the jets one by one in each carb. Blocked low speed air jets will also make it rich at low revs.

[eliminator]

So, what happened then?