Speaking of octane. . . what grade do you use?

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Bonwit

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The book says use a minimum of 94 octane fuel, but in parentheses it says (US regular). I'm guessing they're talking about a different rating as our regular is marked around 85-87 at the pump. I'm also thinking that back in '74, when there was lead in the fuel, regular was a higher octane than today.

I've been running the highest grade I can find, usually around 92 thinking I needed it, but now I'm starting to wonder. Is anyone using the cheapest regular? Any problems?
 
I put in 1 to 2 oz. of Lucas Upper Cylinder Lubricant, 2 oz. of Marvel Mystery Oil and a half gallon of 110 octane racing fuel into a 5 gallon can and fill it up with 4 and a half gallons of Sunoco Ultra 94 octane. It will bring the octane rating close to around 98. My Combat has not complained. Been doing this for the last 5 years. Pipes get blue though and don't care.

Ride Safe
 
You can try lower octane fuel to see what happens. If there is detonation go to the next higher rating available. The riders manual says 94 octane as alternative to 96 for 850 engines 8.75:1 compression ratio. The recommendation is to increase main jet form 280 to 300. For my combat at 10:1 compression ration, recommended is 100 octane with 28BTDC timing and 220 main jets. Alternate is 97 octane, 250 mains and 26BTDC timing. I'm using California rated 91 octane, 26BTDC and 240 mains and still getting some detonation. Just switched to the next colder plug, BP8ES and will see how that works during this weekend's club ride. I tried 260 mains because I had them, but ran poorly. Would be nice to have a dyno to tune with.
 
For my 850, I understand 89 octane (US R+M method) is recommended. Frankly, I've run it for a couple years on 87 before reading that and have seen and heard nothing untoward. I too put in a bit of Lucas upper cylinder lubricant (or whatever else I have around the garage to try to ward off airhead valve recession at the time), but that's about it. I don't think our Commandos are particularly needy in the fuel department. I'm running a Boyer at stock advance, not retarded, in case you wonder. 8.5 is pretty low compression ratio, not surprised it's not requiring more octane/less advance.

As always, YMMV and I'm happy to be educated by the more knowledgeable than I (who surely outnumber those LESS knowledgeable than I...)
 
Bonwit said:
The book says use a minimum of 94 octane fuel, but in parentheses it says (US regular). I'm guessing they're talking about a different rating as our regular is marked around 85-87 at the pump.
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The book octane recommendations will be RON rating, as used by much of the world.

As BrianK has pointed out, US/Canada use a different system to determine octane rating.

http://www.torquecars.com/articles/fuel ... atings.php
http://www.btinternet.com/~madmole/Refe ... ONPON.html
 
I believe the US octane rating system chas hanged from the time when the riders manual was published. In 1973 my combat ran very well on Chevron premium with lead that had a 100+ octane listed at the pump. Regardless of the rating system, what's important is if it works. Current US 91 octane unleaded does not work well in my combat. The strange part is until a few years ago I didn't have a problem (detonation). Something more recent has changed. I suspect the ethanol. The idea of lowering the compression/performance of a combat is repugnant. Special fuel mixes are only practical if the ride is within range of that source. If I'm not able to resolve the detonation, may have to resort to an 850 purchase for longer rides. :(
 
Fuels are constantly being reformulated, and it's never a good thing for our motorcycles. My Semi-Combat is still running ok on premium. Who knows how long that will continue though.

I wonder how hard it would be to convert a Commando to bio-diesel... :?:

Debby
 
"Current US 91 octane unleaded does not work well in my combat. "
Click to expand...

Ever try this stuff?

http://volvospeed.com/Reviews/octane_bo ... lucas.html
Speaking of octane. . . what grade do you use?
 
British Only Motorcycle and Parts, Inc. have these Cal Products Rocket Fuel that come in a 1 oz. packet that increases the octane rating 4-7 points. Also it states on the product it helps protect the piston and heads, aids valve & seat lubrication. Part # 32-70140 for about $1.82. Treats 2-5 gallons. Small enough to put in tool box or any storage area.
 
Just by the way, on the pinging Combat have you tried to clean out the carbon with water? i can't recall how long since you top end was off since I have trouble remembering my own seven bikes. Anyway it would not take much carbon at all to make a Combat ping, and the old water treatment might make it better.
 
Cookie said:
Just by the way, on the pinging Combat have you tried to clean out the carbon with water? i can't recall how long since you top end was off since I have trouble remembering my own seven bikes. Anyway it would not take much carbon at all to make a Combat ping, and the old water treatment might make it better.
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Hi Cookie,

The head was off last season to replace a left exhaust valve guide. There is little if any carbon build up. I tried a bottle of Lucas Oils Octane booster this year with slight improvement, but didn't cure the problem. 240 mains, 26BTDC and BP8ES plugs seem to be doing it. I'll know more after the club ride tomorrow through Napa and Sonoma valleys.
 
Have fun David, I used to live up there and it's pretty. Traffic on route 12 can be a bear though.
 
I use the Sunoco 94 octane in Penna.
I add 2-3 oz of lead additive for "off road use only" mind you from walmart.
Have not noticed any power loss in my 72 combat. Throttles right up to 70-80 mph.
Fast enough for me at age 47.
Plugs are a nice light brown and dry. NGK BP7ES?
I do add Marvels Mystery oil from time to time to keep the top end clean.
I have 9,300 orig. miles on mine and ride it like it was new.
I have the factory carb set up and looks like a strobe timing check shows 28 degrees.
MarshalNorton
 
I tend to tinker with a bike for quite a while and finally get it sorted to the point where I'm happpy with it and it is reliable.
During this time I just use premium grade from the local gas station. The ones I drive everyday, my yellow Goldwing and Red Chang get regular grade wherever they are low on fuel. My spare runner 76 goldwing LTD has been getting regular with fuel additive.
The Norton is closing in on being sorted to the point where she will sit until I want it. I'm thinking of the local airport for aviation fuel for her. I reckon she will use a few tanks a year in my use and the good stuff will prevent clogged carbs and such. Fuel is so bad now that the extra expense may be well worth it.
 
Any body leaving fuel in their tank and carbs should be adding Sta Bil fuel additive.
Cheap and found at Walmrt. Don't forget to run through carbs not just add to tank.
I've been doing this for a few years in all my engines to include snow blower and riding mower
No problems in the spring just start and run
Figured since we were on fuels this info maybe be helpful to a new/or returning rider of vintage iron.
In the past we just drained or ran out everything.
Marshal
 
I can't recall if it has been mentioned on this board but a lot of folks have switched to Marine Stabil. The other stuff, which unfortunately I have a lot left of, is not working so well with the alcohol.
 
Cookie said:
Just by the way, on the pinging Combat have you tried to clean out the carbon with water? i can't recall how long since you top end was off since I have trouble remembering my own seven bikes. Anyway it would not take much carbon at all to make a Combat ping, and the old water treatment might make it better.
Click to expand...

What actually is the "old water treatment?"
 
I've heard debates of why this works and I'm really not sure. Perhaps some experts here can tell us. An age old carbon removal treatment is to take off your car air cleaner and rev the engine to maybe 2,000-3000 RPM. You then trickle a small stream of water into the engine, not enough to stall it, just enough to make it stumble a bit. I first saw this on flathead Fods and Chevy sixs as a kid.
Currently I know folks do it to Subarus that get high mileage and a few folks have done it on the Goldwing board I frequent. Both of these type engines often run over 140,000 miles or so and get carboned up.
It would be a little harder to do it on a Norton but I'd think it would work.
As you know I'm sure in the fifties water injection was advertised in Popular Science, I imagine that kept the carbon out.
Seafoam is alo often used for carbon removal but I've never tried that.
 
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