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Gnarly + Boyesen + removed snorkel= rejet needed?

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Jan 24, 2004
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#1
I have a 2003 KDX200 and just freshened the top end with new piston, rings, etc., cleaned and properly timed the KIPS and it's running great. My question is, I have a new set of Boyesen power reeds, and a Gnarly pipe sitting in my shop, ready to install. The only thing that is not stock is that the snorkle has been removed from the airbox. I'm in the Southest (GA) and I'm wondering if the pipe and reed combo will require a rejet? The FMF website suggests the stock jetting and Boyesen states that I may have to go down 2-3 sizes on the main jet size because the power reeds tend to make the engine run a little richer.

I know, I should just install the parts and go from there, but I'd really like to hear from someone in my area that has the same mods to see if any rejetting was required. I hate getting into rejetting a bike, but will if needed.
 

_JOE_

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May 10, 2007
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#2
Sure, you MIGHT be able to get away without rejetting. The only problem is that you could be wasting alot of money on bolt-ons if you dont tune the bike for the mods. I cant see changing any engine part without ensuring proper jetting. Just because a bike runs reliably doesnt mean it is running at its full potential. The whole point of adding the parts you want is to increase performance, and they are alot more expensive than a few jets. Jetting isnt hard if you understand it all works. I strongly suggest Erics book. It explaines it in good detail. On my bike I can change the main and pilot jets through the drain plug in the float bowl. It seriously only takes less than five minutes.
 
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Aug 21, 2005
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#3
Yes, rejet it. The pipe might not require it, but the reeds do. Anything that changes the amount of air that moves through the engine will change the fuel requirement a little.

I once had an occasion where an exhaust change required no rejetting, and an upgrade to K&N filters claimed to require no rejetting, but when combined, a significant airflow change occurred and the bike wouldn't exceed 25 mph without a bit of tuning (the jetting was definitely worth the work). It was a streetbike but the principles of airflow apply to all internal combustion engines.
 

G. Gearloose

Pigment of ur imagination
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#4
cripes, they need rejetting from the factory, just do it.
 
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Jan 24, 2004
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#6
Just pulled the bowl. It already has a 155 main. Stock is a 160. Guess I'd better do a plug chop before going any further huh.
 
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Jan 10, 2008
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#7
yeah it wouldn't hurt and would give you a base.

I would have though the combo would require richer jets b/c they would make the engine run lean - more air through the motor on both ends with same fuel - i don't get it.
TNutcher
 
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May 23, 2008
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#8
Ha i put a 35mm carb on a 1998 kdx 220 that had the 33mm and i put a fmf gold series k35 pipe on it and i also put the boysien reed pedals on along with a new ignition filter with the air box lid removed any idea idea on jetting the bigger carb came with 150 main and the 33mm had 145 i was thinking 160 main thanks any info would be good! any one ever try this set up thanks?