Home. Back. ...... The Gas Gas Guru. Technical Information.
Q. My riding buddies say I should run race gas in my bike. Is this necessary? It costs alot and is sometimes hard to get.

A. Each bike's octane requirements are slightly different based on a number of variables, such as compression ratio, combustion chamber design, jetting, riding conditions etc. Most Trials bikes (with under 170 lbs cranking pressures) do fine on 92 or 93 octane pump gas. (*NOTE* - Gas Gas recommends at least 95 octane)
One of the possible symptoms of a need for higher octane is the 'pinging' or metallic rattle from an engine. This is sometimes noticed when the throttle is 'chopped' (closed quickly) or when the engine is under heavy load (full or partial throttle), like a hillclimb. Try retarding the ignition timing slightly (about .5 mm at a time measured at the stator plate) and see if that doesn't clean up the pinging. This will also tend to make power delivery smoother and you may find this better for your riding style. Make sure your jetting is correct for your riding area.
I run a 50/50 mix of race gas and high-octane pump gas. I like the extra octane as a 'reserve' in case I have a problem with overheating (clogged radiator) or changing atmospheric conditions that don't suit my present jetting. Race gas stays 'fresher' longer (at least three weeks in a well sealed steel container, plastic containers are porous) but I add a little gas stabilizer just in case. Just be sure to mix a batch of fresh premix each time you ride. As for you Ute Cup guys, you might find that you have LOWER octane requirements. Race gas burns slower (thats one of the ways it resists detonation) and the lower cranking pressures at altitude sometimes call for faster burning gas for better performance and ease of jetting.

Professional tuner and 'Trials Competition' writer Jon Stoodley has very kindly stepped up to the plate to answer your questions. If you're having problems, or need some advice just send an email to Jon. If it's something that could be useful to others, we'll post it on the site.
This article originally appeared in 'Trials Competition', and was reproduced with permission.
Home. Back. ..... The Gas Gas Guru. Technical Information.