Hi Jeffery,
The carb is measured at narrowest point deep inside, typically where the needle goes through,
much like this drawing shows:
As for the boost bottles and the haters, no worries.
I've had Yamaha and KTM motorcycles that came with them stock.
Have removed then to see their effect. A good system works.
So, for full throttle jetting, how can you be sure of the jetting?
First off, check diligently that everything else is right:
- no leaks at the carb, crankseals, gaskets, engine case.
- sparkplug gap is right, makes a bright yellow spark at rpm
- carb float is set right, no dirt in bowl
- Tank screen or filter is clean, plenty of fuel flows to the carb
Buy a new plug in the heat range you have been using. Give the bike a few full throttle runs.
Pull the plug and have a look. It would be nice if it were as simple as this:
but this is not where you need to look,
you need to look deep into the insulator:
To do so, the experts often use a bright light and a magnifying glass.
When the mixture is very rich you will easily see the huge amount of soot,
but as it gets close to optimum it gets very hard to see the "mixture ring".
So what do we do?
Cut the plug to get a better look:
Here is a good progression to give you an idea of what you will be looking for:
So one more time, someone else describing what you need to do to determine jetting:
And here is one of the best graphics I've seen on reading a plug:
Here is an excent slide show to understand carb tuning:
http://www.slideshare.net/J.T.A.JONES/carburetor-theory
Steve