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Old 07-04-2012, 05:41 AM   #1
judobiker OP
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KDX200 Tuning Help

Here's the deal: I bought a '01 KDX with low hours. I put a fresh top end in it fairly recently. The jetting on it when I got it was 48 pilot, 160 main with stock exhaust and snorkel removed. It was rich, so I went down to a 45 pilot and 155 main. That seemed to be just about right with great throttle response everywhere.

When I started doing harescrambles, I decided to do some upgrades and replaced the exhaust with a FMF Woods pipe and silencer. The low range power seemed to pick up with just a little less at the higher end of the range. A couple of weeks later, I replaced the 11 year old reeds with Boyesen Dual Stage Reeds. Bottom half of the rev range is awesome, but at about half throttle it drops off and doesn't want to rev. I'm finding myself getting dusted by 125's on straightaways and having to do excessive downshifting on hills--and that just ain't right.

l'm in Georgia at about 800 feet above sea level. I've been running 87 octane mixed with Motul synthetic at 50:1, BR7ES plug. The plug always looks good when I wipe of the oil.

Anybody got any tuning ideas or a good baseline for the main jet and needle? Or should I junk the Boyesen reeds and go back to the stock ones? I feel like I've spent a fair amount of money to get my bike slower
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Old 07-04-2012, 06:33 AM   #2
scrambler73
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In my experience, these bikes aren't super sensitive to jetting unless you start getting into ported (highly tuned) engines.
Every one of my KDX200's or 220's have had an FMF woods or fatty (or pro-circuit), with close-to-stock jetting. Im at 950 ft above sea level so we should be close.

All of that said, Im not an out and out "Expert" on trying to get the last Nth-degree of power out of them... I've had a bunch (insert shameless plug for the 2 I have in the for sale section...lol) and all of them run just fine. Some had aftermarket reeds, and once again, all have had chambers (FMF or Pro Circuit pipes).

One thing I am an expert on (Ive got a few melted pistons to prove it) is that on a two stroke engine that gets its neck wrung, The highest octane fuel you can feed it, the better..up to a certain point.
Detonation (pre-ignition) is the enemy, and if you are starting to find yourself jetting "lean" to get power, you are going to be putting another piston (and possibly worse) sooner than later. 87 Octane is just asking for trouble....

At the very least run 91 or 92 Octane pump gas. Im not saying its going to "fix" any of the lack of power issues, but it may save your engine.

There are a few bright guys over at KDXrider.net. Someone should know exactly what you need to get every ounce of hp out of it, without the flat spots..



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Old 07-04-2012, 07:09 AM   #3
JeffS77
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my guess since this happned after installing the new reeds You maybe sucking air around the intake where it mates to the cylinder...give it a look....and run the highest octane you can find...hell even my '79 KLX250 with a mega 18hp Kawi recomended 95 octane ..your KDX needs the good stuff.
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Old 07-04-2012, 02:32 PM   #4
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Thanks for the replies. I went out and messed with the bike a while today and I think I found the culprit. The needle had worn a little microscopic lip on it. I went with the KDX/KLR budget fix and polished it smooth with some cloth. When I put it all back together--shazam! The throttle response was back. Back to fourth gear wheelies. I guess I needle to order a new needle for the longterm...
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