reg vs prem gas query

[RANDHALL]

New owner of a 1976 90/6. Bike is stock, 23,000 miles. Do I need to use premium unleaded gas, or can I go with regular? Why? Thanks for any/all input. Rand

 

[skiteach]

I've always run prem in my /5. It hurts these days-11 gal tank!

 

[bobh41]

Interesting gasoline tidbit

To understand octane rating, you need to understand a little bit about how car engines work.

The engine’s power comes from carefully controlled explosions of gasoline/air mixture inside the engine. To control the explosions, the gasoline must burn at exactly the right rate. This is controlled by the gasoline’s chemical composition.

Gasoline is a mixture of many chemicals that burn at different rates. One chemical that burns at the right rate is isooctane. A chemical that burns too quickly is n-heptane. To describe how fast a gasoline burns, a scale was developed using these two chemicals. Isooctane is defines to have an octane rating of 100, which n-hepatine has an octane rating of 0. Octane ratings compare the burning characteristics of gasoline to mixtures of isooctane and n-hepatane.

For example, if a cheap gasoline burned the same way as a 50:50 mixture of isooctane:n-heptane, the octane rating would be 50. Gasoline with an octane rating of 87 burns he same way that a mixture of 87 percent isooctane and 13 percent n-heptane would burn.

from pa.msu.edu/sciencet/ask_st/101696.html

I've always used the highest octane I could find. My /6 began to ping under load (uphill for example in top gear at around 3500 rpm). I had it tuned up and it doesn't ping at all.

 

[ZARINELLI]

Use the ...

New owner of a 1976 90/6. Bike is stock, 23,000 miles. Do I need to use premium unleaded gas, or can I go with regular? Why? Thanks for any/all input. Rand

... minimum octane rating the owner's manual says you should be using. No reason wasting money on higher octane gas - I am pretty sure you won't "feel" a difference.

 

[Gil]

I use 87 on my R90/6 (1975) and I use a couple of drops of Marvel Mystery Oil in the gas. Just about a teaspoon per gas tank to keep the valves lubricated and the engine smooth. For the last two years I have ran this bike hard and not once I have encoutered an issue.

 

[PHMARVIN]

Hi, Rand,
My first BMW bike was a '76 R90/6, bought new in April '77. If I remember correctly, the owners manual says to run premium, 98 octane leaded fuel. I was transfered to Europe shortly after buying the bike, and it was shipped there. I spent a month in Spain in '78 and many times, 98 octane wasn't available; the best available was 95 octane. The bike didn't seem to notice the difference. Were it me and if I didn't have access to 100LL avgas, I would try running regular. If it didn't ping, fine. That's what I'd run. If it pinged, I'd try mid-grade. Same scenario. Only if it pinged on mid-grade would I think it needed premium.
Ride Safe,

 

[crazydrummerdude]

I put 89 in my R75/6 last week and it ran like crap through the whole tank. Back to 93 and it runs fine.

 

[bigrider]

I use 87 on my R90/6 (1975) and I use a couple of drops of Marvel Mystery Oil in the gas. Just about a teaspoon per gas tank to keep the valves lubricated and the engine smooth. For the last two years I have ran this bike hard and not once I have encoutered an issue.

I was told the Mystery oil is also good for lubricating the slides and other friction prone things on the Bings. I use a teaspoon every other tank of gas. Even if it doesn't work, it makes my gas smell minty fresh. This is very important in dealing with other easily offended airheads.

Dave H
San Antonio, TGX

 

[RANDHALL]

Impressive Support! Thanks to all

One of the factors in my deciding to go with an airhead over other models/brands of motorcycle was the great support network of sharing people. So far my expectations have been exceeded, many times over. Thanks for all your input. I will work through the suggestions, one at a time, to find which works best for my ride.

 

[PAULBACH]

Go with what MOM (Motorcycle Owners Manual) recommends. The difference in price is not a king's ransom. It is the difference in cost between the least expensive and the middle grade and/or high test. On a five gallon tank that delta is usually less than a dollar.

 

[braddog]

I bought both of my '77's used within the last 10 years. Previous owners both said that they always ran the highest octane they could find (92 or 93). I do the same. They both run like tops. No technical details here, just my own experience.

 

[testinglogin]

The previous owner of my R80/7 said he used to run mid-grade (89 octane) through the bike. I found it didn't run well like this, so I always ran premium. I wonder if the cheap gas is what led to my premature valve wear. Since getting new valves/seats (and everything else associated with a new top end), I run 87 octane, but that's because my bike is now dual plugged. If it wasn't, I'd stick with the 91 or 93 octane stuff.

 

[James.A]

I put 89 in my R75/6 last week and it ran like crap through the whole tank. Back to 93 and it runs fine.

This is my experience also.

 

[arebin]

My Airheads will ping on anything less than 92.

My Ducati SS900 will run on 87 with no problem.

Run what don't ping.

 

[The_Veg]

Run what don't ping.

+1

FWIW, my 1995 R100R will run on 87 with no problems at all.

 

[osbornk]

Run what don't ping.

+2

My 86 R80RT has done fine on regular for the 8 or 9 years I have had it.

 

[carockwell]

My understanding is that the pre 1981 bikes were mostly built with higher compression and needed premium gas. The later bikes use lower compression and "may" run on 87 octane. With the aircooled Beetles and Porsche's we found that certain cars were always okay with 87 octane, other cars always needed 91 octane, and some cars could use 87 octane unless the weather got hot and then they pinged so 91 octane was used. The aircooled engines are sensitive to heat and load. In warm weather running at relatively high speed your boxer may need higher octane gas. By the way, the old 95 octane gas in the 60's and 70's would only be rated as 90-92 octane today as we use a tougher octane standard now.

 

[TELLURIDER]

How do you think altitude would play into the equation? I live at 8,800ft and usualy ride between 6,000 and 10,000 it would make sense to me that because of the thinner air that the fuel oxygen mix might be better with lower octane.

 

[ccolwell]

1) Go with the owner's manual as long as it gives an octane rating used in the US. European octane is calculated differently.
2) Check the compression ration for yours (should be in the manual). I believe it's 9.5:1 (my 76 R75 was). That probably needs hight test. Later bikes went to 8:1, don't know when but my '84 R100 was that.
3) Pinging is the ultimate test, you don't want that.
4) Mileage can be a factor -- carbon build up on the piston can increase compression slightly.
5) Hight test is a bargain. It's always about 10c a gallon more, so it's a better bargain the more expensive gas gets.

 

[dougfollett]

Non expert opinion here but what I have heard from reliable sources for automotive engines is that if it does not ping or knock when using regular that it is OK to use it. Some high compression engines will knock with regular. Also not all premium gasolines have the same octane rating. My Caddy says right on the dash and by the gas cap to use only premium. I have used regular for the past 50,000 miles and never had a problem. I also use regular in both my R100RT and my R80RT and they seem to like it. People like to think they are doing something good for their vehicle by using premium but if it doesn't need it, it is a waste of money IMO .

Hoo