What gas should I run in my R69?

[JakeF]

My '56 R69 tends to have a bit of a valve rattle at higher speeds. A R69S owner I met runs his on 101 octane and suggested I blend the 101 into the 91 octane premium I have been running. It seemed to do the trick but I wonder if I am doing the right thing. I am fortunate to have a 76 station right near my house that sells 101 octane out of one of their pumps but at $9.99 per gallon it is not what I want to be burning all the time if I don't have to. I have only put a couple hundred miles on my bike since I bought it a few months ago. I have gone through a routine tune-up (plugs, points, timing) and tank flush, carb clean out, and new fuel lines with inline filters added. Should it run ok on premium? Is there an additive I should use instead? Or do I run it on the 100% 101 octane or 50/50 blend that I am doing now? I am sure this post will stimulate some spirited responses. Let it fly.

[schrader7032]

If your R69 is stock, it came with 7.5:1 compression...far less than the R69S which is 9.5:1. There's no reason to run the highest octane. Pretty sure you don't even need the middle grade. I suspect you could use the lowest octane gas.

Valve rattle at high speeds could be weak valve springs? If you're hearing pining, then you have more wrong with the engine or with timing.

[comet]

Not sure what compression your particular engine is but if what you are hearing is spark knock , pre ignition, be careful as you can hole a piston quickly. I go to a local airport and buy 100 octane low lead aviation gas (in a can). It works great and costs about $4.00 per gallon. The original owners manual states premium gas for the R69S.

[808Airhead]

You can also run Lucas octane booster,it contains MMT and works very well. My R69s has the same valve noise and has for the last 8K miles,it seems fine.

[mark_weiss]

I'm in agreement that your R69 should run fine on pump gas. Maybe premium in hot weather, mid-grade virtually all of the rest of the time. Premium won't hurt anything, but it will require more frequent spark plug replacement.

Have you checked your timing at full advance? Your advance mechanism uses a metal leaf spring to limit advance travel. These springs can weaken and even break off. This can develop into a serious problem.

[robgernstetter]

you could also try a small amount of Marvel Mystery Oil each time you fill up the tank. I use about one ounce per 4 gallons. I agree that premium gas is not necessary, better to find a station that has gas without the corn ethanol mixed in...that will screw up your valves over time.

[VintageSalesandRestorations]

HI,

Your R69 should have a timing retard lever on the clutch perch - attached to the special R68/R69 magneto - Next time you hear that rattle, pull the lever back a bit and see what happens. It should relieve the issue.

Someone may have put higher compression pistons in or - who knows what - It's nice to have that lever though.

Jeff

[Somer]

I agree that the 91 should be fine for the R-69.

I'd double check the timing. Still have the manual advance?

I'm not a big fan of octane boosters. They will leave a residue.

I keep 5 gallons of race gas (110) around. I mix a little with everything as it is more stable and detergent.

You might also experiment with ratios; say 1/4 101 to 3/4 91.

[JakeF]

Thanks to all for the suggestions. I will bundle my responses here. I checked the timing and it is spot on. The 101 octane gas I mentioned mixing is listed as racing fuel. There are a lot of high performance motorheads in my area and so the local Union 76 station has carried racing fuel in one pump for years. Yes, my bike has the manual retard level on the left handle bar. I have had several people say don't touch it after you set the timing but I will try it next time out. The rain has finally subsided so I will probably take it out tomorrow and report back. There is a possibility that the prior owner bumped the compression. I was told it has the domed pistons. The prior owner is deceased so it is second hand info.