Missing at 5500 rpm

[Douglas Money]

My bike starts right up and seems to run fine as long as I stay under 5000 rpm. I pulled the enricher while it was breaking up at 5K and it made no change. I pulled the plugs and #1&4 look fine. #2&3 are sooted but not wet. I checked secondary wiring and it shows 27.5K Ohms from #2 boot to #3 boot with cap in place. I am guessing I have an ignition coil dying and I know the caps were marginal the last time I checked. I have already done the wire replacement on the original coils with solid wire. I have already done the pickup coil repair as I had that happen before and I have the flat fuse block on it for the last few years. This problem has been there for a while but as I stay mostly below 5k, it hasn't bothered me too much. Would just like to see if I can figure out what is causing it.

[motoman]

My bike starts right up and seems to run fine as long as I stay under 5000 rpm. I pulled the enricher while it was breaking up at 5K and it made no change. I pulled the plugs and #1&4 look fine. #2&3 are sooted but not wet. I checked secondary wiring and it shows 27.5K Ohms from #2 boot to #3 boot with cap in place. I am guessing I have an ignition coil dying and I know the caps were marginal the last time I checked. I have already done the wire replacement on the original coils with solid wire. I have already done the pickup coil repair as I had that happen before and I have the flat fuse block on it for the last few years. This problem has been there for a while but as I stay mostly below 5k, it hasn't bothered me too much. Would just like to see if I can figure out what is causing it.

Wire replacement on coils with solid wire? If referring to the plug wires, they were already solid wire originally and molded into the coils. If the plug wire to coil 'fix' had to be done, that is marginal at best, and a 'get U by' thing. If the plug caps were marginal previously, why use them as they are a cheap replacement new? Sorry for the questions, but info is marginal at this point. Either way, first suspect is ALWAYS pri./secondary ignition before carbs or fueling, whether it be automotive or motorcycle.

[Douglas Money]

Yes, I did the plug wire to coil "fix" previously with the specified solid core wire shown in the how to on here. I didn't replace the caps before becuase I didn't have them on hand at the time. Thanks.

[ViperRon]

The resistor caps tend to build up oxidation no matter what you do because of heating and cooling. Once they have a little oxidation it only happens quicker next time you clean them. The caps come completely appart and can be cleaned but like I said once worn you have to regularly check and clean.

You can always do the swap over of all coil wires, plugs, and caps at one time 1&4 to 2&3 and see if the color on plugs change but more than likely the plug color is a mixture or oil issue and has nothing to do with the miss.

Make sure you do not have a kink in a fuel line going to carbs causing lack of fuel flow at high demand or something like that.

If you feel good about your coil wire repair then caps are a first to replace.

[DGXSER]

If your measuring the resistance between plug cap to plug cap, then 27.5k is not a bad number. 5k for each plug cap + 15 for the coil and your at 25, 27.5 is not far off.

Does sound like you may want to check pick-up coil wires.

[TopCatGr58]

Hey Doug,

Pull the caps off, and remeasure the coils ohms, should be ~15K wire to wire, the book/manual isn't specific about this, but the measurement is done without the caps. The caps can also come apart...screw fitting on the inside of the plug section...then you'll find an internal resistor, you can check for corrosion, measure the resistor after cleaning. If still above 5K then the resistor is bad and you can then replace the cap. IF it's within spec, then you can reassemble it cleaning the screw portion that fits into the wire, along with possibly crimping a little off of the wire if you find green corrosion on the copper wires to get to good copper.

T.C.

[Douglas Money]

Yes, I measured cap to cap. I regapped the plugs when I had them out just to be sure. Tonight I had the bike out and while cruising at 70-75 for a while, I could feel the missing cylinder come back and smooth out. It would do that as long as I held the speed with the throttle lock for a distance. Actually the closer I got to 5k, the better it ran, but started to drop out at 5100-5200. I am planning on rechecking pickup coils tomorrow. Thanks.