Topic: Cb550 - missing after short warm up

[reddyvv]

My bike was running super nice before I parked it up for the winter. I started it a couple of times in the late fall and it ran fine. Mid winter when it was very cold I started it up and it began to misfire after warming up for a short while. I dismissed it due to the extreme cold.

Later in the winter I put a Hondaman ignition on, cleaned and adjusted points, checked timing with strobe, etc. Still noticed the misfire problem (erratic strobe on 2+3) but again put it down to extreme cold.

A couple of days ago after finally getting some 50+ weather I started up and it ran superb with the Hondaman ignition, even as low as 500-750 before it warmed up!! As soon as it started to get warm it started to misfire again.

Checked the coils and they measured fine. What's the opinion? I'm thinking that there's a short on the coil when it warms up and those thermal issues are hard to detect.

What's a good replacement coil?
Thanks for any input!!!

[Frostyboy]

Before condemning the coils there's a few things to check.
1. Measure the resistance of the plug caps. 5kΩ
2. Before you put the caps back onto the leads, snip about a quarter of an inch off the end of each lead.
3. Swap the plugs from 2 & 3 to 1 & 4 (just to see of the miss moves if it's still there)
4. Make sure to measure the voltage at the coil + when running. Should be the same as battery voltage. It might need some bullet connections cleaned up if voltage is low.
5. Run it in the dark with the tank off. Look for a lightning show from the leads to the head cover.

[Duanob]

Sounds fuel related to me. Do you close the choke to start it and then open it and it starts missing? Have you checked each the pipes for heat? The pilot jets get clogged super easy with such a tiny jet size. If need be you can remove the bowls without taking the carbs off the bike and remove the pilot jets to give them a good cleaning. I usually have to do this every spring, its part of my de-winterizing process.

[reddyvv]

Thanks for the suggestions folks.

2. Before you put the caps back onto the leads, snip about a quarter of an inch off the end of each lead.

Ding, ding, ding!! #3 wasn't making good contact at the cap. Funnily enough, it would only start missing after 3-4 minutes of running.

[Frostyboy]

Beautiful. Thanks for reporting back.