Fuel

[Frenfroe]

My Jackpiner manual says to use a min. of 95 octane. I assume the same for others and with conservative jetting/timing.

It ran fine on half and half 100LL aviation fuel and pump 93. I never tried straight pump premium because the highest I could get was 93 and I'd rather not cook an engine.....jackpiner pistons are rather hard to come by. I wouldn't use straight aviation fuel either, it's made for very diferent operating conditions. It only costs about $3.50 a gallon versus $6+ for race fuel. I run this in all my bikes, vintage modern, and modern trials, I just vary the oil ratio. (Maxima K2 synthetic at 50:1 for mx/trail riding up to 80:1 for trials)

Frank

I used to run a gallon of VP c12 (112 octane)to 2 gallons of premium. It didn't run as good and I got some fouling plugs with lead deposits.

[Merlin]

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[firstturn]

Merlin,
  I am somewhat familiar with Nitromethane and it's properties, but I can assure you it isn't the only thing that will destroy a engine when it comes to FUEL.  And piston clearance (tight? as you stated it) has more to do with fuel used because of different octanes can create more heat than others and heat on a close tolerance bore to piston clearance can cause a engine to seize.  But I do agree with you on the "stupidity factor" and even some of the best have been fooled by this phenomenom[B)].

Ron Carbaugh

[Lew Mayer]

I would think that a higher octane would burn slower(hence the advanced timing on performance engines)so therefore would actually help keep an engine cooler if the engine is not built to the max. Am I thinking wrong here? and why?

Lew Mayer

[DKWRACER]

What a great post Ron! the stupid factor also sometimes equates to ask a few questions, and to never be afraid.......I tend to shy away from the following mixture: 101 unleaded mixed 50/50 with 91 pump 40:1 Maxima 927...Oh yes Swaintech the piston..Teddy, where are you?
Tom...

[firstturn]

Lew,
  There is a lot of people on both sides of that argument which includes some of my closest and respected friends.  All I can say is I will rest on what I have seen on the same engines run on the different octaines of fuel(gasoline).  The best I have found run in a test lab at a Oil/Gas Refinery was around 98 octaine rating with aircooled 2 stroke engines with Blenzoil/Blendzine oil at 32:1.  I have never had a seizure with this type of mixture with a air cooled 2 stroke engine.
  This is just a forum of what we think so that is my take.  I really don't put a lot of stock in slow burn or fast burn as long as I don't have detonation, hot spots or some type of lean conditions caused by other factors such as carburetion from changine of altitude.  I know this is getting to be an out of control post so I am going to give it a rest for tonight....ZZZZZZZZZZZZ.[:0]

Ron Carbaugh

[TGTech]

OK, my turn. I've spent a lot of time talking to various fuel and oil people about two strokes, and after weeding out the information that I really didn't need to know, here's what I learned. The octane rating of a gasoline, is purely a rating relative to the fuel's ability to control detonation. Detonation can be caused by a number of things, but in race engines, compression and ignition timing are the two most common contributors.

Sachs engines in stock form, are fairly mild, and as such, do not need race fuels. Just to be on the safe side, a high test pump gas should be used. There is one factor there, that you do need to pay attention to, and that is the alcohol content of the gas. Basically, you don't want a pump gas that has alcohol in it, if possible.

If you've pumped up your compression, then you may need to consider some race gas. During the Penton era, we never (to my knowledge) ran any race fuel, and normally, didn't even use high test gas. But, with a few exceptions, we were using stock heads. We did have some cylinder work done to the engines, but the heads were pretty much stock.

The KTM engines, are another story all together. KTM has a history of going after horsepower by using high compression. And this is only good, when you're "riding a dyno". When Carl Cranke built engines for team members, he would actually lower the compression along with doing the port work. These engines were some of the best running engines in the world. Two times during Carl's tenure at Penton Imports, people from KTM took top ends and pipes that he'd worked over, back to the factory for their people to look at and work from. And in both instances, the compression of these engines had been actually reduced instead of increased.

With these engines, with stock compression, it might not be a bad idea to use an octane rating around 100 to 105 in order to keep them cool. However, back in the day, we still used just pump gas in them, and I don't remember a lot of trouble.

Another very important factor with regard to the compression level, is head design. KTM had a very good handle on head design, which is probably why they were able to get away with the compressions that they did.

Another factor to be considered, is the oil mix ratio. Whenever you mix oil with the gas, it actually drops the octane rating. We always used the Hi Point Concentrate (today's Golden Spectro, exactly the same formula as it was in 1968!) at the ratio of 64:1. Why such a goofy ratio? 10 oz. of oil to 5 gallons of gas. I do remember some times, if the bikes were going to be used hard in sand, that we'd go to 4 gallons, which dropped the ratio to around 51:1.

You'll notice, that with those ratios, the octane wouldn't be lowered nearly as much as if you would be mixing the oil at 30 or 40 to 1, so maybe that's why we didn't have trouble with the compression.

As a final note regarding the Golden Spectro. All through my son's racing career with his Kawasaki mini's and 125's, I used Golden Spectro. I did drop the ratio though, because in top level motocross, the engines are used a lot harder than in vintage racing (with some exceptions, I'm sure) or off road racing. And I never had an engine failure that could be attributed to the oil.

I hope this has provided some insight and advice.

Dane

[OUCWBOY]

I miss the days of just pulling up to the Sunoco Pump and mixing your blend right there. I tuned for a few young racers in the 70's who were much faster than most of us now and that fuel was perfect. Anything over 98 octane is just a waste of money. Just my thoughts!

Donny Smith

[Merlin]

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[Steve Minor]

Hey Tom...(DKWRacer) In an earlier post you said "...I tend to shy away from the following mixture: 101 unleaded mixed 50/50 with 91 pump 40:1 Maxima 927...."

Is there something about Maxima 927 that I should know? Its one of the few oils I have to choose from at my local bike shop. No one around me carries Golden Spectro...

Steve

[Frenfroe]

Maxima 927 is a semi-synthetic blend of castor, synthetic, and possibly normal oils with additives that keep everything from seperating. It doesn't cause ring sticking as normal(100%) castor may but smells like the real thing. Sweet!  The K2 that I mentioned is Maxima's best 100% synthetic.

50:1 with 927 may be too thin a mixture for longest engine life, it is a blend. Castor is usually mixed at heavier ratios than normal oils anyway.

I don't hesitate to use K2 at 50:1 in any air-cooled bike......if jetting is correct and timing isn't too far advanced. In modern water-cooled trials bikes we usually mix a 100% synthetic oil at 80:1, some use 100:1. Typically our bikes run over 5 years putting a lot of hours on them practicing, in competition, and ripping from section to section, before they need rings or bearings. That says a lot for modern oils at light mix ratios.

Looking at the posts after my 1st, I seem to have been declared an idiot. My statement was that min. octane requirement in my Penton manual was 95 for the 175. You can't buy 95 where I live. We tend to jet our bikes, in the sake of more power, a little leaner than factory settings. We also may advance the timing a smidgen to get more power. More power=more heat add too low octane and we get detonation, shortened engine (rod, bearings and possibly piston) life, possibly a heat sezure "meltdown".

My GasGas 280 pings like crazy on 93 pump gas, GasGas recommends 95 octane. I could never retard the timing enough and rejet to get pump 93 to not ping. It runs fine at 95+ octane.

The cheapest 95 I have been able to create is the 100 LL and 93 mix. 100LL has little lead compared to leaded race fuels. I don't get any lead fouling on my plugs with it like I got with VP110, VP c4 (112), and other leaded race fuel blends.

Each to his own. I love America!

Frank

[Steve Minor]

Frank......In your opinion....do you see anything wrong with mixing Maxima 927 @40:1 with the high octane pump gas for my 77 400 GS6?

Thanks for the input

Steve

[Frenfroe]

Steve, I realize I stuck 50:1 in where I meant 40:1 on the 927.

IMO,[:0] I know it's not much difference between 32, 40, and 50:1 but I'd err towards 32:1 (4 oz/gallon) with the 927 if I were racing it. Oil costs less than motor rebuilds! I have no problem with the oil itself.

I'm pretty sure straight castor usually gets mixed at 24-32:1, I run synthetics at 50:1, therefore with a blend I'd lean towards the heavier mix.

I have heard, don't know how right they were, that the "927" stood for 9 parts synthetic to(2) 7 parts castor or vice-versa.

Frank

[Merlin]

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[Dennis Jones]

I run Golden Spectro at 50-1 with 93 octane pump gas in all my bikes, lawn mower, weedeater, chainsaw, and leaf blower. I'm not an expert rider or a chemist but with no top end failures in 25 years of using it I think I'm sold on it.

Dennis Jones