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Discussion Starter · #1 ·
So, here is where I am - Airbox removal, K&N pods, Thruxton needles with 2 shims, 140 mains, opened up slide - stock pilot.

Bike runs hard until I get around 5000-5500 - then it starts to stumble. Not sure why, but it is more pronounced as I move up in the gears. Not noticable in first or second. At 4th and 5th gear on the highway it feels like it is running out of gas around 5000 rpm.

Should I move down in my main - 135? - thought I read that if this condition exists you should move down a size or two.

BTW - It is getting dyno'd on Thursday. Will this help me in determining if I have the main jet right?
 

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I had that exact thing happen to me. On the highway 70 plus mph and thought I was running out of gas or bogging down until I backed off the throttle and would run ok. Crank it back open and happened again. I just did the air box cut up with pods, 155 mains, 42 pilots and stock needles and 1 shim. I moved down to 140 mains and problem went away. I've since went to thruxton needles and it's even better overall.
 

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Discussion Starter · #5 ·
Loxpump - I'm right across the river in St. Louis.

I am going down to 135 mains - from the 140's I have in there now. I am getting it dyno'd on Thursday, so I hope that will tell me where my problem is. Since we are having great weather I have been able to do test runs with each mod. I guess I will see how moving down to 135 mains will work. I will leave it at 2 shims for now. Update soon.
 

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Weather has been much improved. Let me know if you like the smaller mains, and especially what the dyno tells you. We do most of our riding on your side of the river. Missouri has better 2 wheel roads, not like our dead flat Illinois ones.
 

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Discussion Starter · #8 ·
Thanks for the offer of the pilots - let me see what the dyno says on Thursday. I'm anxious to see what this latest round of mods has done for performance.
 

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As I understand it, Thruxton needles shouldn't need any shims.... but I know that's not true.

After you've dialed in the main jets and your pilots are up to par, shims are a final step IF needed. You don't go in and add a shim unless or until your main and pilot jets are dialed in.

A shim or two (one should never have to go with three) would address that nagging stumble when you're neither on the throttle or off. If the engine feels like it's starving, bucking, protesting.... and all you have to do is give it a little gas, you need a shim.

I too am curious what kind of pipes you're running. Normally one set of free flowing pipes wouldn't be any different than another set of pipes with regard to jetting. I would replace your pilot with a 42, take both the shims off your needles, take your COLD bike out for a spin and see how well it performs at top-end. If after riding for fifteen minutes your top-end performance isn't as crisp as it was when cold, your main jet was too fat, too rich, too big. Frankly, if you've got a set of good free flowing pipes..... I'm thinking you could go to bigger mains. If you're running TORs or something else as quiet (restrictive), they your 140's could be too big. But don't add shims to the equation until after idle, acceleration, and top out performance is dialed in.

[ This message was edited by: FattRat on 2007-02-21 17:32 ]
 

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Discussion Starter · #11 ·
I went down to a 135 main and it cleared up the top end problem I was having. It now pulls on the top end anytime I roll on the throttle.

It also seems to pull strong from the bottom - and all the way through the rpm range. I guess I could take out a shim and see if that improves anything - or even try the 142 pilot. I am taking it to the dyno tomorrow so I will see what they find out. I will check back.
 
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