2005 CR125 Oil Ratio

Question:

I've got a 2005 CR 125. I can't find out if it's 2 or 4 stroke. I was told to mix it 4oz. to 1 gal. and now it smokes before it didn't. WHY?? {Harmon, US - 2005 Honda CR 125}

Answer:

The 2005 CR125 is a two stroke dirt or motocross bike. Two stroke engines differ from four strokes in that they burn oil in the combustion chamber in addition to fuel. There are lots of other differences that have nothing to do with this question. For a really good explanation of the difference between 2 and 4 stroke engines visit What is the Difference Between a Two Stroke and Four Stroke Engine?.
Some 2 stroke machines will have an oil reserve tank and a pump like the Suzuki LT80 quad. You pour oil in the oil tank and gas in the fuel tank. The injector pump does the job of adding the correct amount of oil to the fuel.
The CR125 is a pre-mix type of 2 stroke. It does not have a separate oil reservoir and injector pump. You must pre-mix the oil and gas before adding it to the gas tank. You can check your owner’s manual for the proper ratio. I believe that the Honda CR125 uses a ratio of gasoline to oil that is 32:1. A gallon of gas is 128 ounces. This means you add 4 ounces of oil to each gallon of gas.

There is a lot of discussion about what ratio is best for what bike. If you are going to be competing with this bike, racing or hill climbs, you will want to experiment to find which premix ratio give you the best performance. Older bikes typically use a little more oil to compensate for worn rings or scored cylinder walls. The additional oil helps to increase the compression.

If you will just be doing a little light trail riding on the weekends and will not have it running at high RPMs for an extended period of time, you can reduce the ratio to 50:1. That would mean 2.56 oz of oil for each gallon of gasoline. You can read more about the technical aspects of pre-mix ratios on Maxima Racing Oils website.


If you use standard automotive motor oil your bike will smoke. You need to use 2 stroke oil. Most modern two stroke oils are specially formulated not to smoke. Look for oils that say 2 stroke motorcycle oil, injector oil or smokeless. I put some examples below.

As you can see there are different brands in a range of prices. We use mostly Bel-Ray motorcycle oil products, although PJ1 is another high quality manufacturer.

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The advice above is assuming that your 2005 CR125 has stock jetting and exhaust. If the bike has been outfitted with a high performance exhaust or been re-jetted, you may need to adjust the amount of oil you use for peak performance.


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