MOPED ARMY

Kold,you've gotta tell us the make,and year of the bike and what type engine.Usually 87 octane reg. is o.k.,but there are some Puchs with 10:1 compression ratios which would be better on 89 octane I'd think.

Maybe your manual had a typo. They may have meant to type 89 instead of 98. Regular gas should be fine (87 - 89). High octane gas will have a harder time burning.

I have run Racing Gas which is still leaded and it runs Super! with no bad effects in my 94 Tomos TT Doug D.

I believe the fellow who told you that was passing along an old wive's tale. There is a lot of nonsense floating around about gasoline (high octane burns hotter, it has more "power", etc).

The only real difference between lower and higher octane is its tendency to predetonation. That is, at high compression, higher octane is more likely to wait for the plug to spark before it starts burning, whereas lower octane may ignite under compression all by itself. (This is bad... it's called "knock" and puts a lot of stress on your engine, not to mention not pushing you forward the way it's supposed to.) That's why high octane is important for engines with very high compression ratios, and the reason the "more power" myth is so enduring. (High compression engines being higher performance, so obviously they need "more powerful" gasoline, right?)

If your ped generally runs okay on regular gasoline, then the only time you may notice a difference is if under extreme load (struggling up a steep hill, perhaps) your engine knocks. If so, you should definitely go with higher octane, since even an occasional knock is very hard on your engine.

I personally just ignore all that stuff and put in the highest octane available, with attention to make sure it's not a gasohol blend. (You definitely want all-petroleum gas). Since I have a 1 gallon tank, I generally add fuel 1/2 gallon at a time, so I can easily mix the oil correctly. The difference between spending 49 cents and maybe 53 cents on a visit to the gas station is, IMO, not worth worrying about.

Just my two (or four? <g>) cents...

Octane is gasoline's resistance to preignition as rated on a scale. The higher the octane number the less likelyhood of preignition (spark knock).

Two methods of measuring octane are available: Research and Motor. The numbers do not correspond between them, but are close. The number on the fuel pump, 82/87/92/101 is an average of the two.

Generally, you should use the lowest octane number that allows you to operate your engine without knocking in the way you use it.

Jim

Don,

If you consider the relationship between piston/crank position and speed of burning of different grades of gasoline, then ignition timing and engine rpm can have a sigificant effect on gas mileage.

As an example, if you have "knocking", you can usually cure it two ways.

You can retard the timing, this allows a greater volume of combustion chamber for the burning fuel to expand into, as the piston is a little further down the bore as combustion is complete.

You could, instead, switch to a higher octane gas. The slower burn rate would have a similar effect to retarding the ignition.

This is a very simplistic view as compression ratio, bore and stroke, engine rpm and temperature all have a significant effect.

Sometimes, running premium gas will allow the engine to run cooler by reducing pressures during the early part of the combustion cycle. Hopefully, this translates into more pressure applied to the piston near the center of its stroke where it can do the most good, possibly improving gas mileage.

Ron

Go to a small local airport w/ private planes. You can get 104 or 108 octane. DO NOT run that in your ped, but if you can get them to let you put it in your car, it does wonders for cleaning out the carb and engine.