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Old 01-27-2011, 06:45 PM   #72
BergDonk OP
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Joined: Nov 2010
Location: Snowy Mountains Oz
Oddometer: 2,980
I've got the FCR up and running and its all good. Smoother off the bottom with no identifiable bog or hesitation. Hard to say yet whether there is any more top end, but maybe the dyno would reveal something, or a longer straight, but its so much more responsive, with snap off the bottom that it never had before. Its also much quieter, the overrun popping is gone, and it just feels so much more refined now.

Thanks to MXRob for the jetting and work he has done in getting there. It certainly makes my life easier when someone else does the hard work.
http://mxrob.com/index.html

The carb I got on ebay was a new 39 and was identified as one from a KTM 450. It cost $250 US + $45 US delivery to Oz. Once it arrived, I checked it out and identified what jets it had in it. A few new jets, some from my collection, and a Flexjet fuel screw and Merge AP spring later and it was time to set it up.

The carb looked very much like the KTM ones MXRob refers to, and is set up for only an opening cable, so likely for a Polaris ATV. I adapted it to suit both stock cables.

Rob was able to supply me with a bell mouth adaptor for under $40 delivered and as I had no suitable billet, ordered one. I stuck it on with some Loctite 641 retaining compound. It was a bit loose, so I used an O ring to provide a temporary seat to hold it square on the carb body while it went off.

I ordered an adjustable PAJ like I have in my Bergs, but it doesn't fit the new carb, so for the moment I'm on the 70 PAJ that came with the carb rather than MXRobs preferred 100. Its amazing how many physically different carbs there are out there that are supposedly the same FCR. If Rob hadn't recommended the 100, I'd likely be going smaller, but right now the 70 feels great.

As I'm at 800 m I jetted a bit leaner than Robs suggestion initially, and have gone a bit leaner since test riding. I'll no doubt experiment further, but for now its very good.

I've never played with leak jets before, as my Bergs do not have a replaceable one, but I have experimented with adjustable AP strokes with some carb mods to make them adjustable, so another learning curve is in front of me as I work through this. The Berg carbs have a boss cast into them that makes this a simple enough mod, but the carb I got does not, so plan B, ie play with the leak jets.

FCR Jetting SD1 800m SD2 800m SD3 800m SD4 800m
Main 155 150 145 150
Needle EMP EMP EMP EMP
clip from Top 3 2 2 1
PAJ 70 70 70 70
Leak 35 35 35 35
Pilot 38 38 38 38
Fuel Screw 2 2.25 2.25 2.25
Float 9 9 9 9
Start 85 85 85 85

At SD4 I'm happy enough, and up to 700 kms to a tank.
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BergDonk screwed with this post 02-22-2012 at 09:12 PM Reason: More jetting tests
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