JSN1200 – Competition 16mm Stroker Freestyle Engine

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JSN1200s are built on order.  There is a 90 day lead time for all JSN1200 engine orders though delivery times are typically faster.

The JSN1200 is the pinnacle of freestyle jet ski performance.  Featuring the world famous CPI cylinder, the JSN1200 is the most powerful 1200cc engine in the industry.  We’ve taken the cylinder that changed the jet ski industry and paired it with an engine package thats reliable and easy to maintain.  Power delivery is linear and controllable – but don’t worry, these engines are SERIOUS arm rippers.

We’ve taken the guess work out of buying a pro-level 1200cc engine.  There are no comp packages, no special configurations and no custom parts.  All JSN1200s are built the same way with the same porting configuration and parts.  The engine you buy from us is the same engine our sponsored pro riders run.

Every engine comes fully assembled and pressure checked.  You’ll have access to a full build profile with every spec down to what type of case sealant was used on our website.  Looking to buy a used JSN engine and not sure how it was originally built?  We’ve got you covered – you can simply enter the engine serial in our engine catalog and find every detail of how that engine was originally built.

Whats Included?

• Assembled Shortblock
  • Nikasil plated CPI cylinder with JSN porting
  • JSN engineered lightweight cases
  • High strength custom alloy cylinder studs and nuts
  • Blueprinted 16mm stroker crankshaft
  • Wiseco Pistons
  • JSN engineered head shell and domes (choose fuel type at time of ordering)
  • JSN power valves,
  • JSN black anodized PV guides
  • JSN black anodized PV caps (raw finish shown in picture)
  • Power Valve boots and retainers
• Intake manifold
  • Featuring an industry first 20 degree carburetor angle for top performance (please verify hull fitment prior to ordering)
  • Includes Speed Plate and throttle bracket
• VForce Carbon Reeds and Cages

Optional Services

• Exhaust manifold port matching (customer ships exhaust manifold to JSN)
• Custom head shell engraving

Notes

• We do our best to offer competitive shipping rates.  However, engine shipping charges calculated at checkout are an estimate.  We will contact customers prior to shipping with final rates.

About the Engine

The JSN1200 engine package was developed with a simple goal: deliver the highest level of freestyle performance while maintaining reliability and repeatability. Every major component in this engine was selected or designed to work together as a complete system. The result is strong low-end response, massive midrange torque, and serious top-end power in a package that remains easy to maintain and rebuild.

Cylinder

The JSN1200 cylinder began as a casting designed by the legendary CP Industries and was further refined specifically for our application. A cast cylinder allows transfer port shapes and angles that simply are not possible with billet or sleeved designs. This cylinder features unique transfer geometry along with large auxiliary exhaust ports and a smooth outlet transition that can only be achieved in a casting.

It is also the lightest cylinder on the market. To keep weight down, improve heat transfer, and reduce rebuild cost, the cylinder is Nikasil plated. There are no cast iron sleeves. Nikasil plating is extremely durable and can often be cleaned and reused for 4–6 top-end rebuilds before a replate becomes necessary.

The cylinder is specifically designed around the 16mm stroker configuration. When used on 10mm strokers the same cylinder is decked and the port heights are adjusted to match the application. These modifications are performed in-house on our 4-axis CNC mill.

We have also refined our own exclusive port timing configuration for the JSN1200. These port heights are specific to JSN and are not available anywhere else. Our CNC porting process minimizes the amount of hand work required which improves repeatability from cylinder to cylinder while keeping labor costs down for our customers.

Crankshafts

All JSN1200 crankshafts are assembled in-house here in the USA. We use high quality crank webs and connecting rods from leading manufacturers and handle final assembly, welding and truing ourselves to maintain full control of the finished product.

Main bearings are Koyo manufactured in Japan, the same brand used in OEM Yamaha engines. The mag-side bearing is produced by our crankshaft web manufacturer and has proven to exceed OEM performance in this application.

Each crankshaft is welded and trued to within .001″ runout. The rotating assembly is balanced for the piston and rod combination used in the engine to ensure smooth operation and minimal vibration.

Crankcases

Designed, assembled and quality checked in-house, our cases are unlike anything else on the market. We were the first to optimize crankcase volume specifically for peak performance in this application.

Our transfer ramp design and tight crankcase volume produce exceptional low-end response while the intake runner design allows a free-flowing intake charge for strong top-end power. The goal was to create an engine that responds instantly off the bottom but continues to pull hard throughout the entire powerband.

These cases are lightweight but were also designed with durability in mind. For example, the crank trenches were designed with enough material to better survive severe engine failures.

For riders building all-out competition skis we also offer optional in-house case lightening. Using our CNC machines we can remove several additional pounds for riders looking to build the lightest possible freestyle setup.

Cylinder Head and Domes

We kept the cylinder head and dome package simple: lightweight, reliable and inexpensive. The JSN head shell features a sleek design and extremely low weight. In fact, it weighs essentially the same as the cast head often paired with these cylinders.

Our dome design is compatible with other CPI-based engines but includes several improvements to address cracking issues sometimes seen with other dome designs. We have sold hundreds of motors and have yet to see a single dome failure.

For customers running other CPI-based head shells, we also offer custom order domes compatible with those newer designs.

Pistons

The JSN1200 uses top-quality Wiseco pistons specifically designed for this application. These pistons utilize a 21mm wrist pin along with an extra wide wrist pin bearing to handle the loads produced by a high-output two-cylinder engine.

We prefer not to use piston dome coatings in this application. In our experience they provide little measurable benefit while making it harder to monitor piston wash during tuning. Keeping the dome surface bare makes it much easier to read carbon patterns and dial in the tune safely.

Intake System

Our intake manifold was designed entirely in-house. It features short runner lengths and an aggressive rake angle which improves airflow and increases carburetor signal for improved throttle response.

The manifold utilizes a 20 degree carburetor angle to help direct the intake charge efficiently into the cases. Our speed plate design uses a large sealing O-ring which gives customers the flexibility to open the plate up for larger carburetors if desired. While the system can accommodate 54mm+ carburetors, we typically recommend 50mm carbs for the best overall performance and rideability.

The intake uses extra-large VForce carbon reed cages originally designed for high performance snowmobile engines. These reeds offer excellent airflow while maintaining strong throttle response.

Starter

The JSN1200 utilizes the OEM Yamaha 62T starter. This Mitsuba starter design has been used across many Yamaha platforms and has proven to be extremely reliable in high compression two-stroke applications.

We continue to use the OEM 62T starter to maintain compatibility with competition rule sets that require OEM component compatibility. Did you know the starters used by 62t, 66e, GP800, GP760, 701, 650, 1200, 1100, etc are all the same?  The 66E platform simply uses a different backing plate.  This starter is model SM-13 and is made by Mitsuba.  It’s used in a vast number of applications.

Manufacturing and Quality Control

JSN engines are machined and assembled in-house using CNC equipment. Cylinders are CNC ported, crankshafts are assembled and trued in our shop, and all cases are inspected prior to assembly. Keeping these processes in-house allows us to maintain consistency from engine to engine and ensures that every JSN1200 performs exactly as intended.