I just got my bike out of the shop. They cleaned and sync'd the carbs as well as replaced the plugs. For the last week the bike has been running really well. Today however I installed my speedohealer on the bike, and filled the tank. I've been reading up on the fuel requirements of this bike. I was running 92 octane, but several people have said that since the compression on this bike is 12.0:1 that this is not necessary. So I filled up with 89 octane. Shortly after thisat idle, the needle blips between 1500 and 1300, and i've had more jerky starts. Does it make sense that the bike would be cranky after changing the type of gas used?

 

My guess is the type of gas doesn't matter at idle on a new motor, usually problems happen under load. I know bike motors are different than car motors with respect to ocane/compression requirements, but my old vette (carbs) has 10.25:1 compression and it requires 97 octane.

If the motor is hunting at idle it could be a vacuum leak or ignition, but in an older bike, maybe you have some deposits in the head or something, maybe timing was changed at the shop, and it may just like more octane. In other words, I have no idea what is going on with your bike, but have a great weekend anyway.

 

My F4 runs like crap on 89. I use shell 93.