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Racer X Tested: 250F Big Bore Shootout

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What is better then a 250F?  One with more power of course.  So, we set out to see just that.  Luckily Jay Clark was able to round up each of the current 250’s for a full big bore shootout.

At the heart of the four Japanese bikes is a Cylinder Works drop-in big bore kit with Hot Cams Camshafts. All of the main parts are available from www.rockymountainatvmc.com. The new KTM 250 motor required a bore and re-plate from Millennium Technologies.

The benefits of the big bore in the Fuel injected bikes is amazing and allows you to have the benefits of a full built race 250 engine without the extra cost and high maintenance. The big bore kits in the fuel injected bikes still “rev out” unlike some previous big bore kits on the old carb bikes.  All of the bikes run well with the stock mapping. However, we wanted better then that so we added a Tokyo mods Vortex box to the Honda and Suzuki. The Yamaha was jetted. The Kawasaki was mapped by Tokyo mods and the KTM had fuel added mainly to the lower end circuit to help in popping. TMR also ported the Honda head to help on power as well. After that the bikes are as close to the same as possible with FMF full exhaust systems. Also Hot Cams camshafts were installed. The Hot Cams new ITR cams are built to use the Stock valve springs and not be too hard on the valve train.

Because of the increase in power the CRF and YZF both got two teeth smaller rear sprockets and the rest of the bike retained the stock gearing.

So, out to the track we went with five test riders of all skill levels to see what they thought.

After spending a day on each bike our group of test riders came away very impressed with all of the bikes. The comments from the test riders on the video say it all. We had tons of smiles from our group of riders who all felt they could win on any of the bikes. However, the RMZ and CRF seemed to be the top two of nearly every rider. It seemed the good handling of the RMZ and big power of the CRF were enough to win over the test riders.


Check out the video to see what you can do to your 250.

 

Here are some details on each bike and what parts were used.

 

#21          Honda CRF250

Cylinder Works 3.2mm Big bore Cylinder Kit 270cc the kit includes a Forged Vertex Piston kit, Cometic Top-End gasket kit and new complete plated Cylinder.  www.rockymountainatvmc.com 800-336-5437

Hot Cams Stage One camshaft www.rockymountainatvmc.com 800-336-5437

 

FMF Racing RCT 4.1 Muffler and Ti Megabomb header www.rockymountainatvmc.com 800-336-5437

 

MotoTassinari Air4orce air boot  $298.00 www.rockymountainatvmc.com 800-336-5437

 

CV4 Silicone Coolant hoses and High pressure radiator cap  www.rockymountainatvmc.com 800-336-5437

 

Renthal 47T rear sprocket(stock is 49),  R1 Works Chain www.rockymountainatvmc.com 800-336-5437

 

Tokyomods Vortex Ignition www.tokyomods.com 888-457-9403

Tom Morgan Racing Head Porting www.morganracingengines.com 949-421-7112

 

VP Racing Fuels U 4.4 – mixed half and half with 91 pump www.vpracingfuels.com 210-635-7744

 

Uni Filter Two-Stage Air Filter www.rockymountainatvmc.com 800-336-5437

 

Dunlop Tire MX51 front 80/100-21 MX 31 rear 110/80-19 www.rockymountainatvmc.com 800-336-5437

 

Tusk Oversized Typhoon front rotor kit www.tuskoffroad.com 800-336-5437

 

Tusk Impact Wheel Set black rims with red hubs www.tuskoffroad.com 800-336-5437

 

MB1 Suspension Suspension re-valve www.mb1suspension.com 951-371-5045

 

DeCal Works Semi-Custom Graphics kit with #’s www.decalmx.com 815-784-4000

 

 

#22         Kawasaki KXF250

Cylinder Works 3mm Big bore Cylinder Kit 269cc the kit includes a Forged Vertex Piston kit, Cometic Top-End gasket kit and new complete plated Cylinder.  www.rockymountainatvmc.com 800-336-5437

Hot Cams Stage One camshafts  www.rockymountainatvmc.com 800-336-5437

 

FMF Racing RCT 4.1 Muffler and Ti Megabomb header www.rockymountainatvmc.com 800-336-5437

 

CV4 Silicone Coolant hoses and High pressure radiator cap  www.rockymountainatvmc.com 800-336-5437

 

Renthal rear sprocketR1 Works Chain, Twin-Wall’s  www.rockymountainatvmc.com 800-336-5437

 

Tokyomods Re-program of stock ECU www.tokyomods.com 888-457-9403

VP Racing Fuels U 4.4 – mixed half and half with 91 pump www.vpracingfuels.com 210-635-7744

 

Uni Filter Two-Stage Air Filter  www.rockymountainatvmc.com 800-336-5437

 

Dunlop Tire MX51 front 80/100-21 MX 31 rear 110/80-19 www.rockymountainatvmc.com 800-336-5437

 

Tusk Oversized Typhoon front rotor kit www.tuskoffroad.com 800-336-5437

 

BLT Suspension Suspension re-valve  951-533-6350

 

DeCal Works Semi-Custom Graphics kit with #’s www.decalmx.com 815-784-4000

 

 

#23         KTM SXF250

The Cylinder Works kits have been great for the 250’s – however, when a new engine comes out the time to get a new model made can take a while. So, for this model we went to Millennium Tech for a bore and re-plate. The stock OEM KTM 250 cylinder has plenty of meat to make it bigger (safely)—so we went over 3mm

You can send your cylinder to Millennium and get all of the pieces in one place.

Millennium Tech Strip, bore and re-plate to 81mm  www.mt-llc.com 920-893-5595

 

Vertex Pistons Big bore 81mm Piston kit www.vertexpistons.com 515-270-2302

 

Cometic Gasket Top End engine gasket kit   www.cometic.com 800-752-9850

 

FMF Racing RCT 4.1 Muffler and Ti Megabomb header www.rockymountainatvmc.com 800-336-5437

 

CV4 Silicone Coolant hoses and High pressure radiator cap  www.rockymountainatvmc.com 800-336-5437

 

Renthal Rear sprocketR1 Works Chain, Fat Bar’s  www.rockymountainatvmc.com 800-336-5437

 

VP Racing Fuels U 4.4 – mixed half and half with 91 pump www.vpracingfuels.com 210-635-7744

 

Uni Filter Two-Stage Air Filter  www.rockymountainatvmc.com 800-336-5437

 

Dunlop Tire MX51 front 80/100-21 MX 31 rear 110/80-19 www.rockymountainatvmc.com 800-336-5437

 

DeCal Works Semi-Custom Graphics kit with #’s www.decalmx.com 815-784-4000

 

 

#24          Suzuki RMZ250

Cylinder Works 3mm Big bore Cylinder Kit 269cc the kit includes a Forged Vertex Piston kit, Cometic Top-End gasket kit and new complete plated Cylinder.  www.rockymountainatvmc.com 800-336-5437

Hot Cams Stage One camshafts www.rockymountainatvmc.com 800-336-5437

 

FMF Racing RCT 4.1 Muffler and Ti Megabomb header www.rockymountainatvmc.com 800-336-5437

 

MotoTassinari Air4orce air boot  $298.00 www.rockymountainatvmc.com 800-336-5437

 

CV4 Silicone Coolant hoses and High pressure radiator cap  www.rockymountainatvmc.com 800-336-5437

 

Renthal   Rear sprocket(stock is 49),  R1 Works Chain www.rockymountainatvmc.com 800-336-5437

 

Tokyomods Vortex Ignition www.tokyomods.com 888-457-9403

VP Racing Fuels U 4.4 – mixed half and half with 91 pump www.vpracingfuels.com 210-635-7744

 

Uni Filter Two-Stage Air Filter www.rockymountainatvmc.com 800-336-5437

 

Dunlop Tire MX51 front 80/100-21 MX 31 rear 110/80-19 www.rockymountainatvmc.com 800-336-5437

 

Tusk Oversized Typhoon front rotor kit www.tuskoffroad.com 800-336-5437

 

DeCal Works Semi-Custom Graphics kit with #’s www.decalmx.com 815-784-4000

 

Race Tech Suspension re-valve www.racetech.com 951 279 6655

 

#25         Yamaha YZF250

Cylinder Works 3mm Big bore Cylinder Kit 269cc the kit includes a Forged Vertex Piston kit, Cometic Top-End gasket kit and new complete plated Cylinder.  www.rockymountainatvmc.com 800-336-5437

Hot Cams Stage Two camshafts www.rockymountainatvmc.com 800-336-5437

 

FMF Racing RCT 4.1 Muffler and Ti Megabomb header www.rockymountainatvmc.com 800-336-5437

 

MotoTassinari Air4orce air boot  $298.00 www.rockymountainatvmc.com 800-336-5437

 

CV4 Silicone Coolant hoses and High pressure radiator cap  www.rockymountainatvmc.com 800-336-5437

 

Renthal 48T rear sprocketR1 Works Chain, Twin-Wall’s  www.rockymountainatvmc.com 800-336-5437

 

VP Racing Fuels U 4.4 – mixed half and half with 91 pump www.vpracingfuels.com 210-635-7744

 

Uni Filter Two-Stage Air Filter www.rockymountainatvmc.com 800-336-5437

 

Dunlop Tire MX51 front 80/100-21 MX 31 rear 110/80-19 www.rockymountainatvmc.com 800-336-5437

 

Tusk Oversized Typhoon front rotor kit www.tuskoffroad.com 800-336-5437

 

DeCal Works Semi-Custom Graphics kit with #’s www.decalmx.com 815-784-4000

 

MB1 Suspension Suspension re-valve www.mb1suspension.com 951-371-5045

 

OEM Yamaha parts www.rockymountainatvmc.com 800-336-5437

YZ125 (two-stroke) air filter cage (no backfire screen)

08 fork guards (larger and now printed Yamaha logo)

 

Jetting Specs- Yes, not till 2014 can you stop worrying about this J

172 Main Jet

55   Leak Jet

45   Pilot Jet

2.5 turns on the Fuel screw

Needle 3rd from top with Yamaha optional needle 5TA-14916-PS-00

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