How to mix fuel for Vintage Motorcycles - 2 Stroke and 4 Stoke

Upper Cylinder Lubricant and Synthetic Two Stroke Racing Oil
Upper Cylinder Lubricant and Synthetic Two Stroke Racing Oil

Four Stroke Engines:

After you restore that vintage motorcycle, or if you have just purchased an old bike and are ready to take it for a spin it is important to consider the age of the motorcycle and the type of fuel it was designed to run on. Nearly all modern 4stroke motorcyles run on unleaded petrol and you need to check with the manufacturer before running the bike on Premium fuel because many recommend that you don't. Modern bikes are specifically tuned for unleaded petrol and the valve guides, pistons and engine timing are all finely tuned to run on this fuel.

Older 4 sroke motorcycles from the 1960s (and before) to early 1980s were designed to run on Super Petrol with Lead added as an upper cylinder lubricant and to raise the octane level. Running these engines without the lead additive will ultimately cause excessive wear to the valve gear and upper cylinder of the engine. The solution is a simple one you can use Premium (higher Octane) Unleaded petrol and add an Upper Cylinder Lubricant.

Upper Cylinder Lubricant can be purchased at all speed shops and many petrol stations. It is not Lead based but it does the same job as the Lead used to do in the old Super Petrol. Just add a few mill to a tank of petrol and you will ensure that the vintage bike you have just lovingly restored will run smoothly and not wear itself out prematurely.

Two Stroke Engines.

Older Two stroke engines come in two categories. Those that used Standard Petrol and had a separate Oil tank for Two stroke oil. Or bikes that used Pre-Mixed Two Stroke fuel.

The bikes that had a separate Two Stroke oil tank used an oil pump to mix the oil with the fuel at the correct level. However some trail bike owners decided to reduce the weight of the bike by removing the oil tank and Pre-Mixing their own fuel. This also reduces the risk of oil pump failure or running out of oil leading to an engine seizure. You have to be very careful doing this, some of the Two Strokes in particular Suzuki pumped the two stroke oil through the big end bearings before mixing the oil with the fuel. This is a process that you definitely can not bypass!!!

Other Two Strokes like my 1973 Honda 250 Elsinore will happily run on Pre-Mixed fuel.

One of the hardest choices you have to make is what ratio of Oil to Petrol should you mix. The more Oil, the more Lubrication but the more smoke and Sparkplug fouling. The less oil, the less smoke, and smoother running but the closer the tolerance before the engine will seize due to lack of lubrication.

The First number one rule is don't use cheap Two Stroke oil designed for Motor Mowers or Chain Saws. Use premium grade synthetic two stroke racing oil. Check the manual that came with the motorcycle, if you don't know then ask. My Honda Elsinore is recommended to run 32 to 1 (32 parts of unleaded fuel to one part of Oil) In a 5 liter tank than means adding 150ml of two stroke oil. Or 20oz of oil in 5 Gallons of Gas.

I however play it safe and run the bike on 25 to 1 (200ml of oil to 5 liters) Generally speaking you can't go wrong with this mixture. The Oil bottles usually come with a mixing formula on the back of the bottle. If you mix the bike with a slightly higher oil to petrol mix the worse that can happen is that you foul a spark plug and cause more smoke.

I have a range of clearly marked Fuel Containers in my shed. Each bike has its own fuel container with its name on it and the mix of fuel inside the can. It is amazing how many people don't take this very important precaution and it cauld cost you dearly if you put the wrong fuel in the wrong bike.



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Comments 7 comments

Mike 6 years ago

You know your stuff, I bought a 72' Kawasaki H2, 750 3 cylinder two stroke, it had been sitting for 12 years in an indoor storage room. Like you said, I changed the fluids,cleaned the carbs,checked everything over, new plugs of coarse and she fired up in 4 kicks!! I removed the oil pump etc, I just don't trust a 38 year old pump, I would cry if it seized because of it failing or the cable breaking. I premix at 40:1 with a great oil I find here, its called AMSOIL INTERCEPTER. Its a 100% synthetic two stroke oil. I also use an oil caled REDLINE, which is also snythetic. It still smokes when she's warming up, but after a few miles, it almost stops. But I do believe its time for some newer rings soon, still has great compression,,140 all three cylinders. I also did what you said in the beginning after starting it,,I rode it carefully,slowly for the first little while. I still do, but the power is there when I need it. Love them old two strokes! I'm keeping this bike for a long time.

Cheers,

Mike


Rick 5 years ago

Be careful when changing the fuel oil ratio. When you increase the amount of oil that is in the gas, that means less gass will be passing thru the carb jets. In other words you can make your 2 stroke run lean. You can actually seize a 2 stroke because you gave it too much oil


Jay 5 years ago

I have an old Elsinore too, and prefer to use the oil tank and pump for my oil source, and forego mixing. Do I need to add anything to the gas, or is modern 87 octane unleaded (with ethanol) fine for this application? Thanks!


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Patrick Colford 4 years ago

Hello all, just a quick question, I have a 1970 Kawasaki, I just restored it, but the problem is i'm getting to much oil, the think smokes like crazy, wondering if i can by pass the oil tank, and just premix my oil? Anyone done this before with a 2 stroke kawi? Wondering I can just drain the tank, and run premixed? Thanks


Denise 3 years ago

Hello I was looking on you website and was wondering please could you tell me the fuel mixture for a suzuki RM250 1993, we have been told that to use 100ml to 5 litres of petrol is that right, as there is no oil pump on these bikes thanks


Todd Breeding 12 months ago

I have a 1970 Harley Davidson Baja 100 looking to get riding. Looking for mix ratio.

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