Max Power-RPMs builds the most durable and fastest YZ 125 big bore and stroker engines in the world. From the AMA legal YZ 134, YZ 139, YZ 144, and YZ 151 to the legendary Vet Class weapon, the one and only YZ 167. Nobody offers the selection nor has the track record with YZ125 big bores kits as Max Power-RPMs.
Click here for more performance options for your YZ 125
| $825 | We Modify your top end. |
| $150 | Exchange top end - Call for availability - Additional Charge |
| CALL | "Bolt On" - Includes Cylinder, head, and power valves (prices vary by year) |
YZ134 Specifications: |
Fits 1997-Current YZ125 |
| Bore: Yes | Stroke: No | Actual Displacement = 134.23cc |
| Engine Modifications Required: | |
| Cylinder: | Bore, Port and Replate with Apticote 2000 ceramic bore coating. |
| Power Valves: | Machined to match big bore ports. |
| Head: | Rechamber to work with the Big Bore piston. 100 octane suggested for most conditions. |
| Crankshaft: | No crank mods required. |
| Crankcase: | No crankcase mods required. |
| Blueprint: | Calculate deck height, squish clearance, trapped volume, port timing and compression ratio and list on your perminant Spec-Sheet. (Some operations with install only) |
Notes: This kit requires you to send us your cylinder, head, and powervalves for modification.
Notes: Core parts subject to inspection before credits will be issued.
Click Here to order this kit now!
| $875 | We Modify your top end. |
| $150 | Exchange top end - Call for availability - Additional Charge |
| CALL | "Bolt On" - Includes Cylinder, head, and power valves (prices vary by year) |
YZ139 Specifications: |
Fits 1997-Current YZ125 |
| Bore: Yes | Stroke: No | Actual Displacement = 139.07cc |
| Engine Modifications Required: | |
| Cylinder: | Bore, Port and Replate with Apticote 2000 ceramic bore coating. |
| Power Valves: | Machined to match big bore ports. |
| Head: | Rechamber to work with the Big Bore piston. 100 octane suggested for most conditions. |
| Crankshaft: | No crank mods required. |
| Crankcase: | No crankcase mods required. |
| Blueprint: | Calculate deck height, squish clearance, trapped volume, port timing and compression ratio and list on your perminant Spec-Sheet. (Some operations with install only) |
Notes: This kit requires you to send us your cylinder, head, and powervalves for modification.
Notes: Core parts subject to inspection before credits will be issued.
Notes: Click here to see a dyno chart.
Notes: This is as large as we go with the bore on a stock stroke YZ125. By stopping at 57mm we keep all the fun parts of the YZ125 and just add a bunch of power everywhere. Line the YZ139 up against any big boreYZ144 and the difference will become clear quite quickly, the 139 revs way farther and pulls longer with little to no vibration.
Click Here to order this kit now!
| $1125 | We Modify your top end. |
| $1199 | Exchange top end - Call for availability |
| CALL | "Bolt On" - Includes Cylinder, head, and power valves |
| $1575 | Installed and Blue Printed |
YZ144 Specifications: |
Fits 2005-Current YZ125 |
| Bore: Yes | Stroke: Yes | Actual Displacement = 144.08cc |
| Engine Modifications Required: | |
| Cylinder: | Bore, Port and Replate with Apticote 2000 ceramic bore coating. |
| Power Valves: | Machined to match big bore ports. |
| Head: | Rechamber to work with the Big Bore piston and stroker crankshaft. 100 octane suggested for most conditions. |
| Crankshaft: | Stroker Crank Pin Included. |
| Crankcase: | Crankcase mods required to clear stroker crank. Click Here for picture. |
| Blueprint: | Calculate deck height, squish clearance, trapped volume, port timing and compression ratio and list on your perminant Spec-Sheet. (Some operations with install only) |
Notes: Core parts subject to inspection before credits will be issued.
Notes: This is the ONLY YZ125 stroker kit we will sell as a "Bolt On" because the crank does not require balancing.
Notes: The YZ125 does not work the greatest at 144cc when it is all done with bore. The transfer ports drop too much and it gets flat feeling with alot of torque and no rev. The Max Power YZ144 uses a smaller 56mm bore combined with a stroker crank modification. The piston is much lighter than stock so balancing the crank is not necessary. A bore only YZ144 is not even close to the power of this kit. The Max Power YZ144 has a nice torquey feel on the bottom and just screams all the way past where a stock YZ125 falls off the pipe. This kit makes an awesome schoolboy class weapon. If Yamaha built a YZ144 they would do it like this.Click Here to order this kit now!
| $1650 | Send us your engine and get a 151cc big bore/ stroker kit installed. |
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YZ151 Specifications: |
Fits 1997-Current YZ125 |
| Bore: Yes | Stroke: Yes | Actual Displacement = 150.55cc |
| Engine Modifications Required: | |
| Cylinder: | Bore, Port and Replate with Apticote 2000 ceramic bore coating. |
| Power Valves: | Machined to match big bore ports. |
| Head: | Rechamber to work with the Big Bore piston and stroker crank. 100 octane suggested for most conditions. |
| Crankshaft: | Stroked and balanced. |
| Crankcase: | Modified to clear stroker crank. |
| Blueprint: | Calculate deck height, squish clearance, trapped volume, port timing and compression ratio and list on your perminant Spec-Sheet. |
Notes: This kit requires you to send us your entire engine for modification with kick starter and shifter.
Notes: Prices listed are to install stroker kit parts in good condition engine. Should your engine need rebuild parts there will be additional charges. We will call for approval before we install any parts that will have additional charges. (example: rod kit, mains, main seals, trans parts)
Notes: The YZ151 is a top end monster. This is the kit we recommend for "A" class and "Vet pro" riders who want to stay on their 125's but hate getting yarded by 250F's on the straights. It has much more torque than the stock engine and revs out even further than a stock YZ125. It makes more peak horsepower than most mod 250F's so if you can keep up with them on a 125 you will have no problem beating them with this mod.
Click Here to order this kit now!
| $1750 | Send us your engine and get a 167cc big bore/ stroker kit installed. |
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YZ167 Specifications: |
Fits 1997-Current YZ125 |
| Bore: Yes | Stroke: Yes | Actual Displacement = 166.82cc |
| Engine Modifications Required: | |
| Cylinder: | Bore, Port and Replate with Apticote 2000 ceramic bore coating. |
| Power Valves: | Machined to match big bore ports. |
| Head: | Rechamber to work with the Big Bore piston and stroker crank. 100 octane suggested for most conditions. |
| Crankshaft: | Stroked and balanced. |
| Crankcase: | Modified to clear stroker crank. |
| Blueprint: | Calculate deck height, squish clearance, trapped volume, port timing and compression ratio and list on your perminant Spec-Sheet. |
Notes: This kit requires you to send us your entire engine for modification with kick starter and shifter.
Notes: Prices listed are to install stroker kit parts in good condition engine. Should your engine need rebuild parts there will be additional charges. We will call for approval before we install any parts that will have additional charges. (example: rod kit, mains, main seals, trans parts)
Notes: This is it, the one and only YZ167. It is our most popular kit for the YZ125 and it has been for many years. This kit is very popular with Vet racers of all levels and works well no matter how you ride it. It can be lugged like a 250 or screamed like a 125, it does both equally well. Put a flywheel weight on it and it is one of the best woods engines you will ever find. If you are looking for a budget bike build up the best years for this mod was 01-03 followed closely by 05-Current.
Click here to see a dyno chart.