Motorized Bike Tips & Tricks: Gas & Spark Plugs


After doing just a couple of motorized bike builds, I started to get into the routine of telling the new owner a few small tidbits to help them out…and reduce the number of emergency calls that I invariably would get. Things like the gas to oil ratio, the bolts and nuts that are more likely to loosen, and a few small things to check if perchance the motor didn’t start.

And despite my instructions, a newbie owner will almost always call with one question or another…almost always. But I really don’t mind. I maintain my cool, and don’t chuckle, and always ask if they had put in fresh gas and changed the plug. More often than not, one of these two will correct the deficiency and the motorized bike is once again at peak performance.

Here’s what I tell folks about the gasoline they use and buy…

NEVER use gas that has alcohol in it…the E10, E15, ect. The alcohol in the gas destroys any viscosity that the oil provides the lower crankcase and piston/cylinder. I have seen the results of this personally in both 2 cycle lawn equipment and motorized bike engines.

After that I suggest the higher octane rating the better, up to 98 or so. As low as 87 is acceptable, but expect a performance hit. On both mileage and power. The ratio I usually run is 28:1. How much oil to add to the gas depends on the brand of oil you are using. Look on the back of the bottle and the amount of oil to add to the gas is in a chart on the back.

After adding the oil to the gas, you have about 30 days before that gas is very weak, and may not start the motorized bike at all…even though it still works the lawn mower or other equipment. A China girl likes a little more octane rating…

About the spark plug…

When it comes to spark, a China girl will take almost anything that conforms to the following dimensions:

  • 14 mm diameter
  • 1.25 threads p/mm
  • 1/2 in. reach. 12 mm and .427 in is good too.
  • Resistance and heat range can vary, but general dimensions must not.

Usually, the stock motorized bike engine kit comes with a really weak plug that isn’t even marked with a manufacturer. But here are some that will fit:

  • NGK – B5,6,7,8HS, BP5,6,7,8HS, BPR5,6,7,8HS, BPR5,6,7,8HIX, (I have tried all of these except the HIX series.)
  • Motorcraft – AER32
  • AC Delco – R44F
  • Bosch – WR6BC+, WR7BC+
  • Accel – 0453
  • Champion – L82YC, RL82YC, L86C
  • Denso – Iridium IWF20
  • Autolite – XS4093
  • SplitFire – SF265F, SF412C  (I’ve included these even though they are discontinued. If you have found a suitable substitute to these please post it in my forum, or in the comments section below and I’ll add it. In the meantime, if you think you have $20 or so to spend, here’s a link to a new racing plug that looks promising…and they can replace almost every plug listed in this article.)


All the information I listed on the gas came from personal experience. Many of which are long stories.

The information about the plugs I credit a (very) little to myself and personal experience, but most of the credit goes to Down South, an elite member of the forum. His post on plugs is here…