Bonneville America Forums Forums Technical Forums Performance Mods 140's or Not

The current setup on my 03 TBA is - AI removed, Bub Slash Cuts, 130 Mains and UniFilter. I have TBS needles but haven't installed them. My bike backfires a little, but not a lot. I do keep an eye on the rubber caps which have cracked and created a poor seal in the past. I will soon take my bike in for the major service that includes the valve adjustment. I plan to have the shop install the TBS needles while they have her apart. My question is - should I replace the 130 main jets with 140's at the same time?

Why? Al

Good question. You should only made changes if you are having problems.

For instance, are you changing to the TBS needles because you have a flat spot at mid-RPMs? That's the only reason to do so. Are you considering bigger jets because you have a problem with top end speed?

If it's running good, don't screw with it...

Run the bike above 3500 RPM's for a few miles, grab the clutch, shut down the engine and coast over to a safe parking spot. Let the engine cool a bit and check the colour of the sparkplugs, they seldom lie about the mixture.

Thanks. I was using the 130's with my TOR's. I'm assuming the Bub's are more free flowing than the TOR's and I'd heard about other guys using bigger jets with them. My bike does run pretty good....it just backfires (not to be confused with popping) a little, but not a lot.

why wait for the shop to install your needles.
you can do it yourself in 10 min.
just take the 4 screws out of the top of the carb,
lift up the slider ( slowly ) and take out the old needle.
reverse.
your done.

If it backfires out the exhaust, you probably don't need bigger main jets. If it pops back out the carburettors when you open the throttle while running at 65 or so you might, but try it with the TBS needles first.

Have you bike tuned with the aid of a dynamometer. It save a lot of guess work and gives you the most bang for your buck.

Thanks for the input guys. Maybe I'll try to install those needles myself. If it's that easy I can just replace them with the originals if the change has a negative effect on performance.

Hi Paul,

This might help too:

http://www.bonnevilleamerica.com/forums/...=true#Post37094

I forgot to respond to Greybeard that the occasional backfiring is on decel only. Phil, thanks for the link. I'll check it out when things slow down at the office. Shakey, when I go in for the first valve adjustment I'll ask them if they have/use a Dynamometer. Thanks again everyone.