octane rating for r80rt

what octane should I be using in a 86 r80rt, stock engine.

93. If you can find it, ethonal free. I for a period ran the cheap stuff (87) and found problems with fuel lines, poor carburation, carb problems. My view is pay a little now or a lot later. Besides the engine runs better on 93.

8.2:1 compression engine...I would think you could use the lowest grade. If you hear pinging, go to the next higher grade. If you need premium, you've got some serious issues with build-up inside the combustion chamber.

But . . . check out GasBuddy.com for ethanol-free gas in your neck of the woods. Around here only a few stations carry it, and it's generally only the premium (93 octane) that they carry. From everything I've heard, the extra cost is worth it.

Eric

Devils advocateeee

Up until a few months ago I was mixing 1gal of aviation gas with every fill up, my tank is a 6.25 gal tank, so roughly a 1-5 mixture. This on a european market bike R60/6 1974, ran perfect for twenty yearssss no pinging. I live in Texas, it's hot and humid so this helps greatly. Now I have tuned the carbs, moved the needle up 1, installed the thicker cylinder base metal shim (gasket,,,) pinging is gone, slight loss of power but I don't have to mix anymore. Not like the R60/6 had that much power anywaysss.
Make sure...NOT JET FUEL! Avgas as its known.

It should be be stated that running Avgas on the road is considered illegal. That said, 4-5 years ago, I bought 5 gallons of racing fuel from my local HonKawSuzYam dealer...VP racing fuel?? It was something like 104 or 110 octane. I mixed some of this in every tank on my /7. It got to be difficult, not to mention dangerous and toxic, to continue to deal with the leaded fuel so I gave it up.

20774 said:

It should be be stated that running Avgas on the road is considered illegal. That said, 4-5 years ago, I bought 5 gallons of racing fuel from my local HonKawSuzYam dealer...VP racing fuel?? It was something like 104 or 110 octane. I mixed some of this in every tank on my /7. It got to be difficult, not to mention dangerous and toxic, to continue to deal with the leaded fuel so I gave it up.

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Exactly well stated, that's why I stopped using it. It did however help greatly, I cannot say that it did not. Avgas is different from racing fuel, 1. The octane rating is roughly 100. 2. The lead in avgas helps prevent detenation in airplane piston engines because of the high compression ratios, and leaning procedures associated with different altitude operations during just one flight. Example, one flight starts at sea level then climbs to ten thousand feet where the pilot has to manually lean the mixture setting to get best power settings, then back down after a few hours. This type of operation is hard on an air cooled engine, this is exactly why the aviation industry is still trying to find an effective alternative to leaded avgas....I say still trying too because the replacement for lead is just such a complicated issue, even the FAA admits to the difficulties in finding an alternative. I also want to make it clear that the amount of lead in avgas is miniscule. I used it because it helped my airhead, I've been running my R60/6 for over twenty years on my mix and the internals look great my valve seats are in awesome shape. BMW's design of the airheads is that of its aviation history, every time I look at the engine I cannot help but see its similarities to that of an airplane piston engine. Yes it's illegal to use avgas on the road. but it was great when I had it.

Reading all the replies in reference to which octane is best for the R80RT -collecting all data: ORIGINAL manual reports 87 octane...some have put aircraft fuel mix, (high octane) into their bike, yet, others, 93 octane, etc.

In the reading, nothing appears absolute. The choices seem to be all over the board! I've concluded, if all fails, stick to the manual, if it pings and bings, try another gas. And, become a disciple to the one's that have surpass the 100,000 mile trek on one motor. And inject a little trial and error. My thoughts for the day.

Since reading this post (and being a concerned scientist), I've been conducting a little experiment (full of bias, lack of replication, etc...).

I've run 91 octane in mine for as long as I can remember... Over the past two weeks, I've run a tank of 91 octane (10% ethanol), mid-grade (89 octane, 10% ethanol) and regular grade (87 octane, 10% ethanol) on my regular commute to work. I could not tell any difference between the 91 and 89 octane gas. I have noticed a (very) little pinging at load (going up a steep bridge with a headwind, opening the throttle aggressively below 3500 rpm, etc) on the 87 octane, but not with the higher grade fuels. At this point, I'm certainly less concerned about using the lower octane fuels compared to before reading all of this and checking it out myself. Your results may vary...

BMW guidance on minimum ÔÇ£pumpÔÇØ octane is clear ÔÇô 87 if you are referencing the ÔÇ£AKIÔÇØ (RON+MON)/2 measurement method used in the North America, or 91 if the reference is the ÔÇ£RONÔÇØ measurement method as used throughout Europe.

However, it is BMW's qualification that states, ÔÇ£fuels containing ethanol or other oxygenates (e.g. ethers and ketones) or methanol, may cause driveability, starting and stalling problemsÔÇØ which causes problems with modern fuel blends.

I do not get any significant driveability, starting and stalling problems running 87 AKI with 10% ethanol with my 1993 R100R or my 1994 R100RT. I do get better fuel mileage when I have the opportunity to run ÔÇ£pureÔÇØ 87 gas.

Along the ÔÇ£there is always someone worse off than youÔÇØ line, I have been looking to add a late-ish model Moto-Guzzi Breva to my stable. These bikes, and others in the MG range, have plastic gas tank and plastic fuel filters inside their gas tanks. Modern fuels are said to be the cause of why some tanks become distorted in use, and most filters collapse. ThereÔÇÖs an all-metal fix for the filter. No fix for the tank.

rstrauss said:

The added heat from ethanol made one of my exhaust valves drop

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Ethanol burns at a lower temp than gasoline. Running fuels with ethanol will result in lower operating temps in the engine, not higher.

Oak writes that ethanol can lean out the mixture, resulting in higher temps. So, unless other changes are made to compensate, ethanol will actually burn hotter.

So a 10% ethanol mixture in gasoline is going to result in too lean of a mixture?

I'm skeptical.

It's mentioned below Figure 2 on this page:

http://www.ext.colostate.edu/pubs/farmmgt/05010.html

Towards the bottom of this page are suggestions for carb changes to vehicles made after 1935; according to them, failure to do so will result in a leaner running engine.

http://www.thecarburetorshop.com/Ethanoluse.htm

BMW must have missed the memo when they designed the oilheads! Talk about lean machines... But I blame California for pushing the designers into too much change too quickly. Before the engines were ready for ethanol it was forced into the market.

Speaking of Octane, Is it true that one should add a 'lead" product to the fuel for an older, (1973 R75/5)?
I can only get gas that is allegedly 10% ethanol.
According to the BMW manual, leaded , high octane fuel (93) should be used. Any ideas on this?

In general, adding some sort of lead enhancer only lightens your wallet. The only true fix is to perform a top end. At some point, you'll need to do the pushrod tube seals, and that would be the time to send the heads off.

The plan at this point would be to set the valve clearances (I recommend 0.15mm intake and 0.20 exhaust) and then monitor the clearnaces at 5K miles intervals. If they begin to close up significantly and you're now starting to check every 1K miles, you've probably reached the point of concern. And any additive probably won't have saved you by much...maybe added another 10% of so??