Sproket combo's

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barefootbob
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Sproket combo's

Post by barefootbob »

Wondering what most of you are running, I have a kdx220, rebuilt motor. I had Ron at RB Design shave the head and do his famous carb mod and I'm currently running 13/48 for sprockets and also I'm 210lb. Motor runs great, very responsive and a beast on top but I expected more down low grunt so I thought maybe something wasn't right with by kips valve until I watched this video my bike is basically doing the same thing. This guy went to a 13/50 combo and fixed the problem. I'm debating if I should go to the 50t rear sprocket or put a 12t on front. I ride mostly single track.
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John_S
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Re: Sproket combo's

Post by John_S »

I wonder if someone along the way has retarded the timing on your bike giving it the screaming top end but sacrificing the bottom end power. Have you ever checked the timing? You usually hear people describe their 220 the opposite of yours. Lots of low end and flatter up top. I played with the timing on mine back and forth between slightly advanced and retarded and you could feel the loss in the low revs. I ended up putting it dead center (stock) and left it at that. Mine came with a 12 tooth front and I run a 13 on it. For me it blew through 1st and 2nd too quickly. It felt like 1st was a granny gear only but I don't have technical hill climbs in Florida.

Edit: I see now that the motor is rebuilt so you just set the timing on it recently.
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SS109
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Sproket combo's

Post by SS109 »

In that vid he was either in too high a gear, bad engine condition, and/or no clutch use.

I run 13/48 gearing as well and do some very technical hike-a-bike stuff. I have never needed anything steeper but it can make things easier at the expense of top end and a little more shifting. The KDX is not a four stroke so using the clutch is important. Also, even though Ron jetted your carb, it's up to you to make sure it is correct for your given parameters and to adjust accordingly. A lot of low end power is found in proper jetting. The condition of the engine also makes a huge difference as well. Hows your compression, reeds, silencer, plug, timing, air filter, etc.?

The only thing steeper gearing does is get the engine rpm's up higher for any given speed giving the illusion of more torque. Yes, mechanically you have increased the torque advantage but you already had the same torque if you just use the clutch!
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barefootbob
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Re: Sproket combo's

Post by barefootbob »

When I took it apart I marked where the timing was. I didn't see a mark for the stock timing position, maybe I should re-visit that. I thought with a 12 on front 1st and 2nd would be to low, 1st is low enough as it is. I'll see if I can find any info showing me how to identify the stock timing marks.
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doakley
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Re: Sproket combo's

Post by doakley »

I’m running 13/49 on my stock 220 and it gives me a great 2nd and 3rd. 1st is a little low.
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SS109
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Sproket combo's

Post by SS109 »

Even with 13/48 gearing 1st gear is pretty useless. I normally take off in 2nd and only use 1st when I'm working my way through very technical slow terrain.
Youtube Channel: WildAzzRacing
AZ State Parks & Trails OHV Ambassador - Trail Riders of Southern AZ
Current KDX: '98 KDX220
Old KDX: '90 KDX200 -White/Blue
'11 GasGas EC250R
barefootbob
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Re: Sproket combo's

Post by barefootbob »

Ya that guy is not using his clutch but I do and have no problem just down shifting when needed. Things get a little interesting when I down shift and it hits the power band on a muddy hill. I had a fun moment Saturday we where on some single track that must have been graded not to long ago, it looked good but once on the trail it was sloppy. I was going around a turn, totally in the throttle, the bike hits the power band witch I'm ok with and then all of a sudden I must have got in some good dirt because the bike hooked up and I was having a whiskey throttle wheeling around a turn moment. I will pull the plug to see if I'm running to lean, the motor runs to crisp to be running rich. The motor is fresh, new everything. Maybe I'm just expecting to much, it's still a very fun bike to ride. Anyone ever put a kx250 motor in the kdx frame :lol: I really like the close wheel base on the kdx, it fits the way I ride better then other bikes I've had.
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