MX LITES 125, 144, 153cc 2-STROKES
The FIM and AMA have strict limits for motorcycle racing and we can help you get the most for your racing class. We have experience in mx, off-road, dtx, hill-climb, trials, road-racing, and atv, karts.
BIG BORE CYLINDER PACKAGES $500
The best value for your money is a top end big bore kit. We can make the biggest difference in performance with the top end because we include porting with our kits with mods to the cylinder head and powervalves to suit your choice of fuel. The package deal starts at $500 and include the top end parts like the piston kit, bearing, and gasket kit. The displacement choices are based on model availability and the choices are 134cc +2mm, 139cc +3mm, and 144cc +4mm. Details of prices and model kits is listed on the Big Bore Masterlist page of our site.
We offer a free service of fitting the big bore cylinder to the crankcases that includes R&R of the top end, case and head adjustments, and evaluation of the engines’ crankshaft. For brands like Suzuki, Yamaha, and TM this is necessary and you can always do it yourself using our photo-instructions on the page titled Super144 Casemods.
All of our kits feature replacement parts that are easily available through multiple sources and 24/7 on-line ordering from our Paypal shopping page.
What’s Included?
All of our kits include cylinder porting, head mods, and powervalve service. You get you choice of 3 powerbands and 3 fuel types. All the top end parts are included too like a Wiseco piston kit, top end bearing, and Cometic gaskets.
Powerbands and Fuel Types
The 3 powerband choices
- More low to mid-range with a flatter top end. By concentrating the power down in the lower revs it makes a powerband that lugs without chugging yet is responsive enough to steer with the rear wheel. Perfect for technical mountain climbing, single-track, Arenacross, ice-supermoto, beginner mx, short-track and TT.
- More mid-range to top end and a bit softer off the bottom end. This choice is best for expert mx, desert, dunes, dirt drags, beach racing, and dtx.
- Wider smoother powerband with less mid hit in the mid-range. This choice makes the power wider like a 4-stroke but without the harsh deceleration. It’s great for intermediate mx, off-road, hill-climb, and intermediate mx.
The 3 fuel types
We machine your head flat then machine the squish-band and bowl to match your powerband and fuel choices. The fuel types are unleaded pump 92, race gas of 98-110, and E85. Pump gas is the most popular choice because you can also run race gas. E85 requires really high compression, a wide squish-band, and much richer jetting. We offer free updates for 1 year on porting changes and head mods.
APPLICATION CHART
HONDA
CR125 1989-2007
KAWASAKI
KX125 1994-2012
SUZUKI
RM125 1989-2012
(Casemods required, send complete engine or bare crankcases)
YAMAHA
YZ125 1994-2012
(Casemods required, send complete engine or bare crankcases)
HUSQVARNA
CR/WR125 1998-2012
BIG BORE STROKER ENGINE PACKAGES START AT $1,100
For the customers whom want a special engine built to their class displacement rules, we offer the engine rebuilding service of changing the bore and stroke. For example the AMA allows a 125 to be built to 150cc for the Lites class but if you want to race a 125 in the 250 class it must be 154cc or greater. We build 155s to a 58 bore and a 58.5 stroke so smaller stature riders can compete with advantage in the 250 class, based on the overall power to weight ratio.
The FIM has a 150cc limit, so for that racing we might change the standard 125’s engine dimensions from a 54 bore and 54.5 stroke to 56 bore and 58 stroke, or a 58 bore and a 56.5 stoke.
The basic big bore stroker package includes a new stroker Hot Rod crank, bearings, seals, gaskets, big bore piston, overbored and ported plated cylinder, with case porting and assembly labor. Not included is clutch or transmission parts, those are extra and based on wear and tear.
HOW TO GET STARTED
Just CLICK & PRINT a copy of the Service Order Form and follow the directions on packaging your parts for shipping. All the options are listed for services, powerband choices, fuel types, spare parts, shipping methods, and payment options. Click here for the service order form.
FAQs on Big Bore and Stroker Kits
Does the power hit really hard in the mid-range and flatten-out quick?
Typically big bores hit hard and flatten-out and that’s what magazine testers have complained about. The reason is that tuners cheap out and skip a step, cylinder porting. We include porting with all of our big bore kits and YOU CHOOSE the powerband type.
Will I need to buy expensive aftermarket parts to make the kit work?
Our kits work with all stock and aftermarket parts except FMF SST pipes which make big bores run hot, but FMF’s Fatty pipes work great. European manufacturers like HGS (Nederland), DOMA (Belgium), and DEP SPORT (England) make pipes for 144 big bores. There’s no noticeable increase from a reed valve. Silencers make a big difference, long for top end, short for low end. Flywheel weights are only good for single-track off-road. A 1-tooth larger countershaft sprocket makes a big difference and compliments the greater torque of a big bore.
Will a 144 pull a 250F?
Our 144 ported for mid-range to top end has more peak power than the a stock 250F but the four-strokes still have a bit of an acceleration advantage in hard dry conditions and through rhythm sections. The main advantage of a big bore 125 is the bike is much lighter, theres no brutal deceleration, and its easier to ride over rough terrain and holds a tight line through turns.
Does the crankcase need to be grinded to accept the bigger piston?
Most models don’t need case mods with the exception of Yamaha YZ, Suzuki RM, and TM125s. We offer free R&R of the top end with crank inspection and case mods on applicable models.
What about the jetting?
Technically you need to adjust the carb jetting when the air density changes but most 144s can use standard 125 jetting. Normally you have to jet a 144 leaner but some models like the 2006 and newer YZ125s need a richer needle and main which we have available. On the flipside, Suzuki RMs need to be jetted much leaner. Jetting has most to do with where you ride and the average air temperature. On certain models, we supply specific jet needles and main jets with our big bore kits.
What about the gearing?
Always gear for more speed because of the increased torque. Typically you should increase the countershaft sprocket by 1 tooth.
Will the 144cc piston make my bike vibrate? Does the crank need to be re-balanced?
Our custom Wiseco Pro-Lite forged piston kit is the same weight as a stock cast piston, so there are no vibration problems caused by the 144 piston. However if you’re building a big bore, long rod stroker for top end, then you may want to have Crank Works in Tempe AZ change the balance factor for best results.
Will the engine wear out faster or be less reliable?
We build-in reliability with thicker cylinder plating, a coated forged piston, and polished port edges. Our 144cc kits are more reliable than a stock 125.
Is the price of the 144 piston really expensive like RPM’s pistons?
The price of the 144 piston kit is priced lower than a 125 piston, plus our custom Wiseco has anti-wear coatings, more surface area to transfer the heat, lightening slots in the inside of the piston to balance the crankcase compression ratio, longer in length for better stability in the bore, and a smooth intake to boost the engine’s over-rev. Replacement cost is $99 or $150 for the piston kit, gasket kit, bearing, and 3-day Priority Mail shipping! The average service life is 10-30hrs for ring and 20-60hrs for piston changes.
Are their any alternative pistons for the 144?
Eric Gorr of Forward Motion invented the 144 and because of the explosive growth in 144 conversions, many other companies have copied his custom Wiseco design with some minor changes in material, shape, and weight. However the copycat pistons are more expensive.
There are two types of pistons; forged from billet and cast from aluminum alloy. Athena makes the only cast 144 piston, whereas the forged piston choices include our custom Wiseco, Wiseco GP, Vertex, and Woessner.
Our piston is a custom Wiseco and they make their own GP model 846MO5800 which is a bit lighter but 1.5 times the price. The Vertex 23335A uses the same forge tooling as my piston with a different crown shape that is more flat like the Wiseco. The Vertex is the heaviest forged 144 piston. Wossner’s forged 144 piston was chosen by Yamaha for their GYTR kits. We sell our custom Wiseco, their 846MO5800 Wiseco, Vertex, and the cast Athena pistons (for the YZ and KX Athena kits). The Wiseco Athena, and Vertex are more expensive than our piston at $155.
How fast can I get my kit and do you have core exchanges?
Turnaround time is fast because we have many core cylinders in stock for immediate trade-up. And if you have a new cylinder and want to modify it, we’ll stamp your name on it and the time varies by season, longer in the wintertime because that’s our busy season.
ALL INTERNATIONAL ORDERS GET OUR RUSH SERVICE FOR FREE!