CBR1000FL 1990. After running until fans kick in I cannot get the bike restarted. Anyone has an idea?
Plenty of fuel and plugs sparking although slight back or misfire noted when idling.

 

If I had to bet, I say the battery may not be up to the job of cranking a hot engine. And that may be due to the R/R getting old and not putting a good charge on it.

The blackish plugs and misfire, I would bet are from a week spark.

If it were me, I'd replace the R/R and do the stick coil mod. You should do those two mods anyway to burn the modern fuel. You need a hot spark for that. those two things right there are the best bang for the buck to update your bikes ignition and charging system.


Stick coil mod LINK

R/R LINK <--this one is plug and play, I have this one and it charges at idle
rather than the factory one that starts to charge around 2,500 rpm. It your R/R is the factory one and the fan is running, the fan may be pulling your battery down. This R/R will help.

 

Exhaust or inlet valves could be too close, ie gets hot even closer still, causing lack of compression......Possible cause.

 

What is your idle mixture screw setting? If you're lean on your idle mix setting (2.75 turns from lightly seated is OEM factory setting), it could be the cause. I would check one of the outer (#1 or #4) and see what it is. Might experiment with 3turns or even 3.25 and see if that helps. The modern fuel we run is 15% ethanol now, making stock settings lean to begin with. Your popping at idle (a lean miss-fire) is also a sign of a lean idle condition.

 

Starter clutch? When mine went, I had to wait ten or fifteen minutes for the bike to cool down if I had to stop for petrol etc, then it would start.