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Old 03-25-2013, 10:41 AM   #3707
Studly Adventurer
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Joined: Mar 2009
Location: No fixed abode
Oddometer: 501
Originally Posted by beek-02 View Post
Bill is correct to an extent. This really depends on the carb you have. If you are still running a stock bst 40 he is absolutely correct. In my experience if you open up the airbox to much you establish no pressure(vacuum) in the airbox. The reason this is bad is because that is the way that your carb operates. It creates a lag until that airflow velocity/pressure is reestablished. With a fcr/pumper carb open the intake and exhaust as much as possible and let that (and off course the motor itself) be your only restriction. As far as filtration goes, there are many theories, but as long as you are keeping the dirt out and the air coming in your, theory is as accurate as any other. Beek

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Thanks, I'm using an FCR 41/JD jetting and Akro exhaust.
I've refitted the blank side cover before reading the above and soon as I get chance will try it out.

But here's a question regarding JD jetting.
I've set the bike up as per JD recomendations for sea level except the needle is on the top notch and runs perfect now. (ie. I've had to drop the needle 3 notches)

So running at altitude, say averaging 6000ft.
If I change the jetting and needle as per JD recomendations.
Will I still need to drop the needle correspondingly or will it be a trial an error thing?

The bike's being shipped out from UK to Alburquerque and would obviously prefer it to be set up beforehand, although I will take a selection of jets and both needles this time.
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