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Discussion Starter #1
Hi,
I haven't found the thread on this topic so: Is the factory jetting ( pilot jet 38, main jet 98) the best for the Keihin carbs on TB which has no other mods? Some threads mention 40 pilot jet....but what about main jet. Is there any space for improvement, for pushing stock machine up to best limits?
 

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To give you an idea, I am running 125 mains in a bike that has an opened up airbox and stock pipes, so it would have to be a bit smaller than that. Cannot go too far because the airbox is so limiting. I wanted to keep the stock pipes on mine so I just cut a giant hole in the right side of my airbox opposite where the intake is on the left side. Cheap power. ...J.D.
 

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Every bike will be slightly different. How does yours run now?

I have a 1996 Thunderbird converted to Keihin carbs, stock jetting with the fuel screws out 2 3/4 turns and it runs beautifully with a stock airbox.
 

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I threw away the pods and bought the stock airbox and 38 pilots, and 100 mains. I may buy the 98 mains. I'm just trying to put it back to stock, the way my friend's 2000 TBS runs so well. I have a K&N element for the box and also the stock element. They tried everything on this bike over its checkered past, even plowing a bunch of holes in both airboxes. I should never have bought this bike, but it was orange and beautiful. The way I understand it is that the bikes are supposed to pop on closed throttle, so don't try to "tune it out"...
 

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Discussion Starter #8
I've tried open KN airbox, 40pilot j., 150main j., 3 shims( 0.6mm each) under the needle, Free flow muffers...info got from Proven set up thread.......but it didn't run well...kot kot kot..from low end and very poor in mid range....too reach?...don't want to split carbs x- times, relying on Proven set ups failed, so far so back to stock 40/98 jets etc where it runs well,
 

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OP was wondering if there was any point in going larger on the mainjet to get more hp or something. These bikes are all about torque with the cams to suit... If you want more power, get a bike with more hp. I rode Buddy's bike 200+ miles one day in moving, and the bike was perfect stock, with TORs and stock jetting, airbox etc. Meanwhile everyone else is talking about bikes with modified airboxes. That's where the "Proven Set-ups" threaded people are supposed to live
 

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"Open" airbox leaves a lot of room for interpretation. Even slight differences between modifications can make a big difference in what works.

The original question was about stock airboxes. Some members have changed the pilot jet to 40. I'm not sure that will help much. Enriching the idle screw slightly is really all that is called for with the stock airbox, basically going from US spec to European spec. (So, if you're not in the US you're already there). If you switch the filter to A K&N or other less restrictive media then the 40 pilot might be an improvement.

Bottom line, without a dyno run to test things it's up in the air as to whether you're improving things or not.
 
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