Keep in mind that the suggestions posted by others are just that, suggestions.  Every bike is an individual machine, with slight differences, and the settings/adjustments will all be slightly different.  Use these suggestions as a place to start, then test and see how your bike responds.  If all is well with this jet size, or that adjusting screw position, then great, buy if not then adjust your machine until it is satisfied.

For example, take the Supertrapp you asked about.  Depending on whether it is an open can with discs, or the muffler version with or without discs, and how long it is, and the type carb you have (stock of performance version) ... all of those things affect the jetting of your carb and can change the main jet size from 1 to 5 sizes larger ... or maybe even more.  It can also affect the pilot jet size 1-2 sizes.  Lots of variables.


You need to know how to do the maintenance and tuning procedures, so be sure to get the books and use the info on this great site as extra source to help understand the whole thing.

barb36jack31 wrote on 12/31/69 at 16:00:07:

I'm running 157.5. Gas mileage is excellent (52mpg+) and performance awesome. It's definately not to rich at top end. It performs perfectly from idle to WOT.

I chose 157.5 based on what I read here. I'm happy with that choice. I have never pulled the plug for a reading but based on how well it performs I'm sure I'm close to perfect. You're two sizes leaner. I would pull your plug after doing a full throttle run with shutoff in the middle. That is the correct way to read plugs and determine if your main jet is correct. Too rich won't hurt an engine. Too lean will.

we're running a 155, the exhaust is just a bit on the sooty black, but in our low altitude high heat i dont mind, the performance is good, i have a 152.5 for a spare. it really depends on the individual motor and environment that it lives in, but you get the idea of about where it ought to be, to get in the ballpark.