Bonneville America Forums Forums Technical Forums Performance Mods Changes to set-up after big bore?

To anyone who has done the 904cc big bore (mine is going together at the momment), did your bike require any different set-up? for example jet size changes etc.?

I don't predict that anything else is needed but just thought I'd ask.

Thanks for any help

Short answer, no. You will get the same gas mileage too.
You may have to up your jets a little, but I actually went from 160 mains down to 150s. The carbs just seem to be more effecient and can still deliver the gas needed.
Now, once I get the new Mikunis on.....

Cheers Dinqua,
I too will down size my jets a little (after recently putting Thruxton needles in), probably going from 160 to 154. I don't want to be running too rich when I run it in..

Those Mikunis seem to be getting plenty of airplay, hope they turn out to be a worth while upgrade for you!

Running Thruxton needles, you could probably go to 145s or less.

145's...really? has anyone else gone that small with D&D / Freak / Thruxton needles?

You see where I am at with fatter needles from my sig line.
You can't be any lower in elevation than me unless you are underwater!

If you are at a much higher elevation, the jets may have to go smaller than that.

You have 160s in there now, right? Are your plugs black? Mine were with 160s & TBS needles. I dropped to 150s and life is good again.

Ha, yer I'm pretty low at my place...beach front!

Not black, with the stock needles with 1.5 shims they were perfect but now with Thruxtons I have some black with spots of white on tab side, and clean on the open side of the plug. I think I will try either 152 or 154 then once it's run in i'll take it to get dyno done.

Cheers for your advice!

I believe we would all like to see any dyno results.

Good luck!

Thanks,
I will post dyno results when they're done for sure, but it'll be 4-6 weeks from now until it is run in properly (weekend only rider).

Cheers