First Ride ... R75/5, 1970. Fuel question

[schrader7032]

Use the lowest octane fuel the bike will let you use! Basically, you don't want the bike to ping, so you'll need to use the grade of gas that prevents that from happening. If it's going to ping, it will do that when rolling on power quickly, trying to accelerate up a hill, or pushing the bike hard on a hot day. The bike was delivered with 9:1 compression ratio pistons, so likely you're going to need something higher than the lowest grade of gas. Unless the bike's been dual plugged in which case you can drop down a grade.

Here in the US, we three grades of gas, typically ranging from 85/87, 89, and 93 octane, depending on locale and altitude. I believe in Australia, the octane rating system is a little different. Yours is the RON while in the US it an average of RON and MON or something like that.

Every pre '81 airhead will suffer from the use of unleaded fuels. As you said, they were designed for use of leaded gasoline. They run fine with the unleaded variety. But...you knew there was a but coming, right...you'll need to monitor the valve clearances on a regular basis. If the clearances start to close up rapidly, like within 500 to 1000 miles, the valves are beginning to sink into the heat due to the receding valve seat. Set your clearances to 0.15mm for intake and 0.20mm for exhaust and then monitor them on a regular basis.

The problem of valve seat recession is probably more of a concern on the larger displacement bikes due to the extra heat produced. The problem will also be accelerated if you thrash the bike hard. Adding a lead substitute may just be a placebo effect or it could actually do some good. It's hard to say. I've been using ValvTect on my R100/7 and have been pleased so far...90K miles to this point. It's not that expensive per tank...it's pretty concentrated stuff. Just be sure and follow the directions on how much to add...too much and it will foul a plug...DAMHIK.

So, use an appropriate grade of gas, set/monitor the valve clearances, and have fun riding. Likely you won't have a problem until it's time to take the top end off for pushrod tube seals. While it's off for that, might be a good time to have the valves/seats checked out and replaced at that time.

Kurt in S.A.

[VBMWMO]

I'm about to go on my first ride!
had it for a couple of weeks now but I work 7 days usually so this is my first chance.

SILLY question perhaps:

which fuel?

95 regular unleaded?
98 octane unleaded?
Add a few drops of lead replacement fuel additive?

I figure they were made for the old Leaded fuel? Couldn't find any info on it because maybe it's too obvious.