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MX Bob Air Box Mod

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What is the recommended size of the cut out? I did a search and got a few hundred hits and gave up after half and hour of scrolling through posts, not to mention it's two AM and my eyes are getting bleary. Hopefully someone can just pop in the info. TIA

Nick

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the size of the hole would depend on the jetting I assume.

But anyway I believe there is a pic of the full hole mod on Jesse's site (Kientech Engineering IIRC).

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What is the recommended size of the cut out? I did a search and got a few hundred hits and gave up after half and hour of scrolling through posts, not to mention it's two AM and my eyes are getting bleary. Hopefully someone can just pop in the info. TIA

Nick

The goal is no restriction to get the best performance. If you are going to mod the air box there is no sense in only opening it up a bit and then having to play with main jet size. Also the DJ needle taper is set up for maximum air (side cover removed). If you leave restriction through a smaller hole in the top you will trash your upper mid throttle range (too rich). You can always jet the WFO with a different main jet but you are stuck with the taper of the needle. If your needle does not match air flow then you'll have rich/lean spots at different throttle positions based on clip position.

This is what mine looks like:

My_Airbox.jpg

Here is Jesse's box mod:

DR650AirBoxMod2.JPG

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***? whats with all the sponge? :excuseme:

it's a uni filter.

I have it over the top & I have it over the door but I have NO filter in the box.

this has effectively doubled my airbox (filtered) volume.

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The goal is no restriction to get the best performance. If you are going to mod the air box there is no sense in only opening it up a bit and then having to play with main jet size. Also the DJ needle taper is set up for maximum air (side cover removed). If you leave restriction through a smaller hole in the top you will trash your upper mid throttle range (too rich). You can always jet the WFO with a different main jet but you are stuck with the taper of the needle. If your needle does not match air flow then you'll have rich/lean spots at different throttle positions based on clip position.

This is what mine looks like:

My_Airbox.jpg

Here is Jesse's box mod:

DR650AirBoxMod2.JPG

Rob, from the "a picture is worth a thousand words department", that's a big help. Also, I take your point about the air flow, needle and jetting all complementing each other for best results. I am going to order the DJ kit from Jesse tomorrow and see if I will be satisfied with the results from it. If not, then I will suck it up and spend the big bucks for one of the replacement carbs. Thanks,

Nick

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