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Canadian Daves JustKDX
1991 KDX 250. Where can I get Power!!!
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[QUOTE="dirt bike dave, post: 98193, member: 18302"] The engine is basically a mildly ported '88-90 KX250 with a very heavy flywheel; there is power in there with some mods. Before you sink moneyh into mods, make sure the rings and piston are in good shape and the silencer a nd KIPS valves aren't clogged as a result of the stock rich jetting. The stock jetting is way too rich and it is common to modify the slide or replace it with a KX unit with 1mm more cutaway for better low end response. My buddy and I both had KDX250's, can't remember the exacat jetting we used but I think it was a 160 main jet, 38 pilot and one or two steps leaner (higher #) on the needle. Also, for trail riding, you will probably be happier with a B8ES or even a B7ES plug in place of the too cold B9ES. With the VERY heavy stock pipe and silencer but revised jetting, the bike has a strong low/mid hit but does not rev out very well. An FMF pipe will smooth the low end hit out and get you some revs on top, but it is a good low rpm trail motor first and foremost. Use a thinner head gasket from a '88-90 KX250 for more compression and more power. It will run fine on pump premium. Use Boyesen reeds. I had a RAD valve too, worked OK. Got it cheap, but it is probably not worth the retail price. On mine and my buddies, there was tons of casting flash in the intake port - clean it off with a dremel tool next time you do a top end. Also, on both of ours, the openings of the side KIPS valves stick up well above the floor of the main exhaust port when the KIPS are fully open. I used a porting tool to remove some material so that there was a very smooth transition from the KIPS valve to the main exhaust port. This had no negative effects but really increased revs and peak power. Oh yeah, a 13t countershaft sprocket is good for tight trails and will certainly help the bike feel more peppy. Best of luck with yours - it can be a decent running bike with some minor mods. If you want major power, you are going to have to port it, but with minor work it's a nice motor with strong low end for a 250 2 stroke. Also, revalve and respring the forks! The stock fork settings are pretty grim in the rocks and roots. BTW, it is a hard bike to ride wheelies on as the wheelbase is pretty long and the steering geometry is slower than most trail and MX bikes. [/QUOTE]
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Dirt Bike Discussions By Brand
Canadian Daves JustKDX
1991 KDX 250. Where can I get Power!!!
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