Fuel

[rich allison]

You helped me so much with my shock setup on my Piner I've got a question about fuel. What do you put in your bikes? Unleaded reg. or a higher octane? There is a racing shop here that sells Sunoco Racing Fuel that is still a leaded fuel that is 114 octane. I picked some of this up and mixed it with Belray Premix, hopefully this willbe ok. Its been a long time since I've mixed up any fuel.

Thanks, Rich

richard j allison

[Lew Mayer]

Rich,
this is only my preference. I use 50/50 CAM 2 purple and high-test pump gas.

Lew Mayer

[Dennis D]

105 octane leaded from the speed shop and golden spectro 50:1 in both my 72 Piners Dennis D

[firstturn]

One word of caution: Heat  If you are running anything over 100 octaine, have a close bore and you are a fast rider you could have problems.  Please I do not want to debate this, but it is my thoughts and believe me I have accesses to any level of fuels that are made.  Just my take.

Ron Carbaugh

[tmc3c]

I am running 105 with maxim super m 40/1 with no problems. I wish I could find cam 2 fuel here.I used it in my 430 Husky in Charleston and I cut it with 93 unleaded.It would FLYYYY

Thomas Carmichael

[Mick Milakovic]

With all due respect to the riding abilities of everyone in this group (specially guys like "Smokin" Tom Benolkin):  Does octane really mean that much?  I know I'm not even close to the potential of my bikes running straight gas.  

Just for the record, I use Spectro synthetic mixed 50:1 and premium pump gas from the same Shell station every time.  I've never had a problem, my plugs run clean and I'm pretty sure my jetting will remain the same with the same gas.

[rich allison]

I wasn't as concerned about the octane as I was about the leaded unleaded issue. If unleaded works just as good as the leaded racing fuel I will run the pump gas mainly because it is a lot cheaper.

thanks

richard j allison

[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]

deleted

[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