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OIL-INJECTION vs. PREMIX: WHICH IS BETTER FOR YOUR 2-STROKE?

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January 10, 2017
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Dear Boss McKannick,
I bought a used 2003 Yamaha Blaster for a good price and I really like it. My quad came with an oil tank and oil injection system. Some of the two-stroke dirt bike riders I know say it’s best to remove this and run premix oil in the gas instead. What do you think? Is that better than the oil-injection system? Did quads like the Banshee and Honda 250R have oil-injection or not? Thanks for your advice.
Davey Reid
Houston, TX.

Son, you are not going to drag me into the age old debate of injection or pre-mix. No matter which side I take, and back it up with facts, people will take me to task because they had a friend, brother, sister, heard about it from some guy, that had their 2-stroke burn up with oil injection. Or the injection system was removed and the machine has never run better. “They” know what “They” know because they know it! And don’t confuse them with the facts!
Here is some historical background Son. Originally all 2-strokes ran on pre-mix. And the oil was a petroleum based pre-mix rated oil, that never really burned clean. They also came equipped with atrocious ignitions that had so little electrical energy, they could barely jump a 0.020” sparkplug gap. This fouled sparkplugs at low speeds. With the advent of oil injection systems, the de-rigueur 20:1 oil to gas ratio was only fed to the engine at full throttle. At idle, where 20:1 would foul sparkplugs, the injector pump fed only a 120:1 oil ratio. Why? Because there is little load on a 2-stroke engine at idle but at full throttle that 20:1 ratio is needed to keep the thing from seizing up.
Again, back in the day, there were three distinct kinds of 2-stroke oil, pre-mix rated, injector rated and pre-mix AND injector rated. And between different makes of 2-strokes with injectors, they recommended different weight injector oils. So, use the wrong oil type, the engine seizes, use the wrong weight oil and the engine seizes. And they did! This is where the legend of the unreliable oil injection systems got its start. And it persists even today, even though snowmobiles, personal watercraft and street motorcycles with 2-stroke engines have used injectors for decades. Now to bring us up to today, we have electronic ignitions that rarely foul sparkplugs because they actually have some electrical energy to jump the sparkplug gap in most any oil/gas mix. Also 2-stroke oils have gotten much better. Petroleum oils burn cleaner, and the synthetic oils burn very clean. These modern 2-stroke oils also provide exceptional boundary lubrication at extremely lean ratios.
So to answer your question, 250R’s and Banshee’s were billed as racers and injection systems were never considered for them. If you are intent on using pre-mix then you can mix your gas with oil at from 32:1 to as lean as some yahoo claimed he runs his 2-stroke! No matter what the pre-mix ratio, you will feed your Blaster’s engine too much oil at idle and a bit lean at full throttle. However people get away with it everyday because of the cleaner burning, better lubricating 2-stroke oils available today and the more powerful ignition systems keeping sparkplug fouling to a minimum. One final factoid to really confuse you, a leaner oil ratio = a richer gas to air ratio. That means the more oil you add to your gas, the hotter the engine runs because of the leaner jetting. As you have noticed Son, you are not getting my advice; I’m too smart for that. All I will give you are “Just the facts”!

Winston “Boss” McKannick is the Dirt Wheels shop foreman who answers reader’s questions every month in the magazine on the “Dialed In” page. If you’re having problems with your quad or UTV Boss has the answers on how to fix it. E-mail him at dwdialed@hi-torque.com

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