Topic: Octane Requirements for 1973 CB750

[MikeyD]

I have a 1973 CB750k3 and yesterday I inadvertantly filled my tank with 2 gals. of mid grade vs. premium.  I normally fill with premium (93 octane).  Does anyone know whether this difference in octane (89 vs. 93) will make that great a difference in idle, performance, etc. for half a tank?  Additionally, I have a source out here where I can obtain racing fuel (100 octane).  Is this higher octane of any value for the 750's?  Recommendations?  Thanks ....

[kyre]

Unless you've done major mods to the engine, 87 is just fine for these old bikes. I used to run 93 in my bike but since the gas prices are so high I've been using 87 for the last year with no difference in performance.

[bistromath]

No need for 93. I try to get good gas (Shell, Chevron, Mobil) instead of no-name stations, but the higher octane mix won't make any difference to your bike.

[Einyodeler]

Check out the FAQs page:
 
http://www.sohc4.us/forums/index.php?topic=264.0

[Geeto67]

I run 87 most of the time. Only in the summer on hot days will I run 93 octane. the reason I run the premium is that I do a lot of city riding and sometimes get stuck in traffic. On hotter days the extra octane helps prevent detonation from overheating (rocks in a coffee can sound).

[Jonesy]

I have a '73 CB750 and the owner's manual originally called for 91 octane, but that was under the old rating system. The modern 87 octaine by the current R+M/2 method (refered to by Honda in later manuals as "Pump Octaine") is equivalent to the "old" 91. I usually run mid-grade since the combustion chambers are coked up a bit and I get some pinging pulling away from lights.

[jurob]

9:1 compression is low and only requires reg unleaded if your timing is not advanced over stock.