Really wierd misfiring/stuttering problem
Posted: Tue Jun 20, 2006 1:56 pm
Hi folks. Having an extremely wierd problem with my recently bought 94 Kawasaki KZ1000P (cop bike).
The bike misfires heavily (heavy coughing/spluttering) at low RPMs under moderate acceleration. With gentle acceleration from a stop it doesn't misfire, and it seems to run fine at cruising speeds on the highway (or maybe I'm not noticing the misfires at that time). Here's the wierd part: it continues to misfire in exactly the same way when running on three cylinders (any three, it doesn't matter which one I disconnect), but it *doesn't* misfire *at all* if I have only two cylinders connected (again, any two cylinders).
When I disconnect a wire, I "ground" it to the chassis with a spark tester, to ensure that the other cylinder on the same coil is getting a spark. I can disconnect any two cylinders-- on the same coil or on different coils, it doesn't matter. I don't get any coughing at all.
Some info on the bike. It's got a stock air filter and exhaust, stock coils, stock NGK BR8ES plugs gapped to the stock spec of .028. It has the stock Mikuni BS34 carbs, which almost certianly have stock jetting. I am using car spark wires, which have about the same resistance as the stock spark wires (I also tested all 4 wires with a spark tester, and they are fine). The plugs show no detonation or preignition. Plugs 1 and 4 are just a tad on the rich side, while plugs 2 and 3 are definitely sooty (but again, I can ride the bike on just #2 and #3, and it doesn't miss). I have tried connecting the coil primaries directly to the battery, which raised coil primary voltage by 1 volt but did not solve this problem. I've also tried playing with idle mixture screws, no dice there. And the bike has electronic ignition, no points. Let me know if I need to give more info.
So I'm puzzled. Can anyone tell me what's going on?
TIA!
The bike misfires heavily (heavy coughing/spluttering) at low RPMs under moderate acceleration. With gentle acceleration from a stop it doesn't misfire, and it seems to run fine at cruising speeds on the highway (or maybe I'm not noticing the misfires at that time). Here's the wierd part: it continues to misfire in exactly the same way when running on three cylinders (any three, it doesn't matter which one I disconnect), but it *doesn't* misfire *at all* if I have only two cylinders connected (again, any two cylinders).
When I disconnect a wire, I "ground" it to the chassis with a spark tester, to ensure that the other cylinder on the same coil is getting a spark. I can disconnect any two cylinders-- on the same coil or on different coils, it doesn't matter. I don't get any coughing at all.
Some info on the bike. It's got a stock air filter and exhaust, stock coils, stock NGK BR8ES plugs gapped to the stock spec of .028. It has the stock Mikuni BS34 carbs, which almost certianly have stock jetting. I am using car spark wires, which have about the same resistance as the stock spark wires (I also tested all 4 wires with a spark tester, and they are fine). The plugs show no detonation or preignition. Plugs 1 and 4 are just a tad on the rich side, while plugs 2 and 3 are definitely sooty (but again, I can ride the bike on just #2 and #3, and it doesn't miss). I have tried connecting the coil primaries directly to the battery, which raised coil primary voltage by 1 volt but did not solve this problem. I've also tried playing with idle mixture screws, no dice there. And the bike has electronic ignition, no points. Let me know if I need to give more info.
So I'm puzzled. Can anyone tell me what's going on?
TIA!