What gas to use?

[Ragtop]

Does anyone have a preference on what brand or octane gas to use with these bikes? (CT70). I know a lot of older car engines will degrade over time using non leaded fuel.
Is it the same with these old bikes? Does anyone run fuel additives?
Thanks
Rags

[XSIVE]

I just run the cheaper unleaded. I believe it is 87 Octane. No additives. Never had a problem. If your carb is dirty you can get ahold of some Seafoam from Walmart and add to your gas.

At one time I filled with the highest Octane I could get and the bike ran like crap. I suppose it takes more spark to ignite the higher octane so I could have put in a hotter plug but Why go that route?

[Ragtop]

Thanks for the tip on the seafoam, I will give it a try.
So, there is no issue running unleaded fuel in these old bikes then? I know unleaded fuel will eventually hurt the valves and seats in an old car engine that was made to run leaded gas, but I guess it's ok with bikes engine then?
Rags

[Flash]

Here's a blip from an original owner's manual. I see no mention of using a required leaded fuel. IMNSHO - unleaded is fine.

[racerx]

Octane rating is commonly misunderstood. The number is a reference to detonation/knock resistance as compared to gasoline consisting of 100% iso-octane. 87 octane, for example, meant 13% iso-heptane (at one time, anyway). Heptane, a seven-sided hydrocarbon molecule is less stable and will self-ignite at lower temperature than octane (more stable eight-sided hydrocarbon). Iso-heptane actually releases more heat energy than iso-octane. Premium fuel has less heat energy and burns more slowly. It's the slower-burning characteristic that makes premium more knock resistant. In a high-compression engine, the "lost" power is more than restored by the engine's superior thermal efficiency, plus it's a lot cheaper to pay an extra $0.20/gallon than repair a damaged engine.

If your engine doesn't need the higher octane fuel, it won't run as efficiently - a total waste of money. Engineers have spent a lot of time & energy designing more efficient combustion chambers that allow 10:1 & higher C/Rs to run safely on 87 octane...and such engines are much more efficient. That's part of what allows GALYs (Great American Land Yachts) such as Crown Vics to get 26mpg on the freeway...back in the day a 2-ton luxobarge would be lucky to get 15mpg.

I've not seen any Honda bike engines with valve recession problems caused by unleaded gas. Most vintage car engines don't run into problems either, unless they're 1960s-era and driven hard...and the solution is to install hardened valve seat inserts. Prior to the late `50s/early 60s head castings were formulated so as not to depend on lead. Post `71 engines were required to run on low-lead or no-lead. As long as your engine doesn't knock or run overly lean for extended periods near max output, you won't have problems. If anything, unleaded makes engines last longer. The combustion byproducts of tetraethyl lead tend to form acids which can shorten engine life.