hi all!!!

i have problem with ma mc21
when i start bike one cylinder doesn't work (up cylinder always)i have to change new spark plug and it works,bike goes well,but after short time it stops working or next day when i start bike again same problem bike starts with one cylinder and upper cylinder dont work so if i going to ride bike i have to put new plug evry time so what it can be,what can foul plug same cylinder always??? (bike is 100%stock)

did anyone had same problem???please help!!!

A bad coil, bad ignition or more likely a bad carb setup. Have you had the carb off to check all the jets are correctly seated and in the right range for the bike?

And since you're going to be taking the bike apart, you may as well make a start on derestricting it!
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

yeah i had the same prob.when starting up only the front fired to start with but after a while the top would start up.my prob was worn cylinder so low comp.once it had warmed up and a bit of oil had built up the cylinder made some compression and it fired.solution strip down and replace cylinder and piston.try a comp test to start with clean and check your carbs check the spark plug cap and run the bike with a spare plug out of the cylinder and earthed to check the spark.