Kawasaki KXF 2004-07 & Suzuki RMZ250 2004-07
This has to be the most unreliable dirt bike ever built. And the good news is we can help you out. The entire engine is littered with an overwhelming design thought process of planned obsolescence. We have many updates for the lower end, but the top end is what we specialize in. The valve train is the weakest link. The stock cams are soft and the edges don't have enough chamfer. Hot Cams ($320) help the situation by opening and closing the valves softer than the stock cam. The buckets tend to form a tiny round spot in the face and eventually they shatter. Kibblewhite makes hardened PVD coated buckets ($140 set 4) that are far more reliable than the stock buckets. The valve train service interval is extended and the engine gets a boost in top end but sacrifices a bit of bottom end. We perform a valve job with porting ($195) because the stock valve job one is horrible, not concentric at all. The bad stock valve job causes the stock titanium valve heads to break over time and destroy the engine. Kibblewhite Black Diamond stainless steel valves make the biggest difference in longevity. For long-term reliability you need all the parts with valves, springs, and buckets ($550).
On the cylinder head, the cams use half ball bearings and half plain bearings. If the oil level or pressure drop the cams can seize to the plain bearings, causing the engine to lock solid. We can usually fix that problem with honing and polishing of the plain bearing.
Regarding big bore kits there are two alternatives; 262 and 290cc Its possible to bore and plate the stock cylinder to 262cc using a Wiseco Hi-Compression Pro-Lite piston kit ($400). However there are some potential problems with big boring a KXF or RMZ250, a well-used lower end has the potential for snapping the connecting rod. Hot Rod makes a heavy-duty aftermarket connecting rod. The tiny oil sump screens clog easily on this model causing a loss of oil flow that usually causes the exhaust cam and buckets to wear in a round pattern. If you have a 2004 model we can improve the gear shifting with the installation of the 05 shift star and plate ($75).
Overheating can be a problem for the 2004 model due to 2 reasons; clutch slippage and coolant flow. When the clutch slips the crankcase oil temperature increases, stiffer clutch springs from Pro Circuit ($50) and Moose Racing plates ($90) will reduce slippage and engine temperature. Regarding the coolant flow, the problem is duo fold; flow rate and capacity. Boyesen makes a high flow waterpump kit ($150) with an impellor and shaped housing that allows you to change the oil filter without draining the coolant. For big bores, engines run in hot hilly climates, Fluidyne radiators ($365 set 2) are a must have item. Fluidyne radiators have more surface area at the core and the frame is very solid and resists bending. Also the top and bottom radiator tanks are oversized and hold more volume of coolant.