Race fuel, pump gas or a mix of the two?
Here at Re-Do Banshee Parts and Accessories, we get calls from people who have lost a top end on a bike after only short time of riding. Usually, it is someone who bought a Yamaha Banshee, took it out riding for the first time, and doesn’t know how the motor was built, or was misinformed by the previous owner.
Many times this blown top end is a result of not running the correct fuel for the way the motor has been modified -- and the problem could have been avoided. We want to help people avoid this costly oversight, so let’s take a look at why this happens.
The type of fuel that you need to run will be a factor of Compression / Compression ratio, altitude, squish band, and timing. The most common problem we see is people build Banshee motors with higher compression, tighter squish tolerances, and advanced timing. THEN they feed their Banshee low octane pump gas at sea level and BOOM…… you lost a piston or two.
Do a little due diligence on your Banshee before riding it.
You need to determine your compression by using a screw in compression gauge. Remember when checking your compression to hold the throttle wide open and give it 15-20 kicks. Depending on your elevation, the compression can be a little different. At sea level, the compression will ALWAYS BE HIGHER so keep that in mind.Next, you should take the stator cover off and see where the timing is set at. The most common advanced timing on Banshee motors is 4-5 degrees advanced.
If your Banshee does not have a timing plate with numbers on it, take a look at the stator plate where it bolts to the cases (three bolts) and see if it looks like those mounting holes have been ovaled out. This is the cheap way to advance the timing and can typically get you around 4 degrees advance. If the holes are oval, check to see if the plate has been rotated clockwise.
You will be able to tell this if there is some mounting hole visible to the right of the bolt. If there is no adjustable stator plate and the holes have not been ovaled out, then the timing is more than likely stock. The last factor is squish band, however that is a little more technical and less likely to be a factor for this post, so we will skip that one.
What fuel should I be running???
Here's a simple formula we use at Re-Do Banshee to determine what kind of fuel to run, & it has worked great for us for years on 99% of the machines we run.
If the compression is under 150# at sea level --- you are more than likely safe to run 92 octane pump gas.
If the compression is 150 to 165# at sea level --- you should run a minimum of 50/50 110 octane race fuel and 92 octane pump gas, but would be fine to also run straight race fuel.
- If the compression is greater than 165# at sea level --- you should use straight 110 octane race fuel.
If you have a low compression engine (120-140#) using race fuel, or a combination of race fuel and pump gas, it will not only cost you more money but will also cause your engine to have DECREASED performance.
We have had success with these guidelines here at Re-Do Banshee. Please understand that this is just a recommendation. It is not the cure-all for every top end failure on the Banshee. However, this is definitely a great place to start for getting the correct fuel selected - and avoiding detonation and costly repairs.
We hope you enjoyed this info. From all of us here at Re-Do Banshee… keep those motors turning!