Coil or not to coil? That is the question....

[redscott33]

Hello everyone.
I'm new to the forum so please, be gentle.
I need some help with what I think is a dodgy coil. I usually do all of my own spanner turning but I thought I might run this passed anyone out there before laying day some bills for a set of new coils.
I ride an 83 Katana 1000S and I'm getting a miss-fire on reletively new plugs. The first signs started a month or two ago when it would develope a miss after I give it some berries (anything over 4000 revs) and the miss would continue after the revs drop so I would have to limp the bike home. It did not miss so bad on deceleration but it would come back with a vengeance under load. I replaced the plugs as it was a typical naft plug miss-fire. Those plugs lasted about 200kms before the miss-fire returnd. I changed the plugs again thinking I bought a dud plug, but after a couple of trips around the block, the miss-fire resumed. I can clean the plugs (though they are spotless) but no change in performace. I can drop in a new set from the box and it goes fine for a while, then starts missing again. At this point I'm scratching my head.... Jeez, I hate electrical problems......
I just went outside and started her up and she idles fine, but I know that if I take it on the road she will start the miss-fire before I get off the driveway. I have thought about fuel but the new plug syndrome kind of blew that one out of the water. Besides, the miss is more of an electrical miss with it on/off symptom rather than a listfull drop in revs followed by a languished acceleration like a typical fuel problem, if that makes any sense.
The bike has also suffered at high revs for about a year but I've always put that down to a dodgy fuel tap or some sort of fuel starvation. It could be related so I thought I'd add that in incase it gives anyone another clue as to what it might be.
Sorry for the long read and thanks in advance for taking the time to listen to my drivel (and read my poor spelling/grammar).
Any help is greatly appreciated.
Scott.

 

[Guest]

I'd start simple and check the spark plug caps and the petcock. Do you know what cylinder(s) is misfiring?

 

[redscott33]

Thanks for the promt reply chef1366.
It was a bit hard to catch but it was stuttering the other day at idle so I quickly pulled off the tank and whipped a lead off one at a time. It was number one that was giving me the problem (I call number one the far left piston as you are sitting on the bike).
Good advise with the plug caps and petcock. I'm known for going too hard too fast.

 

[Ironriot]

Well after the plug cap and petcock I'd check the connections to the coils. Make sure they're clean. After that I'd run through the electrics. Maybe a short or low volts is your culprit. Lastly an easy way to check if the coil is the problem is to switch it to the other side. We do this for cars to check when a coil's gone bad. If the miss follows the coil on to the new cylinder then bingo new coil is needed.

 

[redscott33]

Thanks for the options ironriot.
At least now I have some logical methods for checking and nailing down this gremlin. Hopefully I will be able to change the coil and keep the miss-fire long enough to pull some leads off again. There lays the crux of the problem. The miss usually goes away at idle so its hard to check which plug is not firing. It happened once so I'm sure I can force it to do it again.
I'll check the easy fixes first and move onto the short circuits and low voltages after that. Fortunately I have a manual to work from for voltages. Before everyone rolls their eyes and says, "why didnt I just go to the manual to fix the problem". I did. No joy........
Thanks everyone for your input and time to write a reply to my question. I hope I can return the favour one day.
Regards,
Scott.