Motorcycle tank capacity

[Stainless1]

RX, The bottle pressure will decrease as you spray, no matter what you do unless you back pressure it with nitrogen.  That happens because the bottle gets cold when the pressure is released, and colder is less pressure.  If you start you bottle cold, the pressure will not change much until the N20 starts to run out.  You should be able to get at least 3 lbs in your bottle if you keep it cool.  How many 15 jets are you planning to run?  Run a lb of N20 through your system and time it.  Using the correct mixture 2 lbs per minute should be about 20 hp.  Run it a tad rich. 
You can search the site for N20 and look at suggestions.  I recommend before you spray anything in your engine you figure out what you are putting in there.   Without flowing your jets you will not know what you are putting in your engine. 
We ran ERC 110k as motor and enrichment fuel with no problem.
Good luck with your project

[racer x]

One jet for each cylinder .I arrived at that 15 number by looking at the available jets that is the smallest that comes with a 10-100 hp kit ( I have not bought anything yet)But 10-15 hp is all I can expect from a small engine . I "think " A 2.5 lb bottle will hold for an under 10sec. spray. As it looses pressure it will sent the mixture rich.That is OK

[Stainless1]

.... But 10-15 hp is all I can expect from a small engine . I "think " A 2.5 lb bottle will hold for an under 10sec. spray. As it looses pressure it will sent the mixture rich.That is OK

If you have 33, and then dropped compression, you can probably get to 50+ with the N20, is the bottom end up to 20 more HP. 
Run the system outside the motor... then you will know what you are adding.  Old rule of thumb... 1 lb per minute is 10 HP... if you use 2 lb in 20 seconds you are probably adding 60 HP... a little much for your motor to start....

[racer x]

I don"t think the bottom end will hold up long at 50 hp but I will find out.

Part of why I only want to spray the top gear is to reduce load to the bottom end.
I do appreciate the advice on testing out side the engine.

I am going to start another thread about nitrous on a 15 ci engine.This thread is about the legality of the tank.