Race fuel/methanol

[PAULRY]

Can anyone offer some information on the following.

I would like to jet a modern day motocross bike on methanol, but I am not certain on how to go about jetting the bike due to the powerjet on modern day carburetors. Without the powerjet it is a easy proposition, one merely richens all the circuits considerably. Does one need to richen the powerjet as well?

Secondly, regarding race fuels. My laymens understanding is as follows, the higher the octane the higher the compression one can run, resulting in improved performance. With this in mind the choice between C12 and U2 seems fairly obvious, run C12 since it is the higher octane fuel. Can anyone offer some insight into which is the better performance fuel for a modified 250 2 stroke engine?

 

[motometal]

which bike? what type of power are you looking for? generally, at some point compression starts to hurt high rpm power although it tends to add low end and mid. Once you set your compression, then you find a fuel that has a high enough rating to prevent knock, although keeping in mind that race fuel has many other characteristics that are important to consider, distillation curves etc. Higher octane than you need may not hurt, but isn't needed.

With the methanol, can you use a carb that doesn't have the powerjet circuit and simplify things?

 

[slider84]

yes you will have to richen the power jet as well. everything needs to flow about 2 to 2.3 times more as compered to petrol, dont raise the compression any more than 13.5 to 1 and dont advance the ignition untill you get it jetted well.

 

[PAULRY]

Motometal/Slider84,

The bike is a YZ250 for motocross applications.

Regarding the powerjet, you have confirmed what I thought was required.

Thanks for the information.