Motorcycle Repair: CB750 starting problem, red herring, octane fuel

Question
Hi Mark,

I've got a '90 CB750.  Lately the bike will roll start and run easily, but won't start via the starter, though it seems to turn the engine over fine.

A friend mentioned the voltage regulator, though I haven't tested anything.

A possible red-herring: I ran through a couple of tanks of 91 octane fuel (usually uses 87), because the mileage increased significantly.  The problem cropped up during this time.  Coincidence, or might this have effected the electric starting problem?

Thanks for your help!
-Colin

Answer
Hi Colin,

Is the engine rotating normal-like with same speed and sounds when the problem is present?

Describe the appearance of the spark plugs.

I doubt the voltage regulator is causing the symptoms. The fuel may be related or contributing to the symptoms.

Reply and we'll go from there. Include your email addy as requested and explained in my instructions. I return tech information files by email.

Respectfully,
Mark Shively