Home > Hop Up Kits > GX390, GX340, 420 Predator, & 11 hp up Chinese OHV
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Hop Up Kit, GX340 - GX390, 420 Predators and 13/15hp, Stage 1 Hop Up Kit, GX340 - GX390, 420 Predators and 13/15hp, Stage 1

Basic kit for improving the performance of GX390s, 420 Predators, 13/15 hp Chinese OHVs. Simple to install, you can expect significant performance increases

Our Price: $58.99
Hop Up Kit - GX340 - GX390, 420 Predators, and 13/15hp Chinese OHV, Stage 2/3 Hop Up Kit - GX340 - GX390, 420 Predators, and 13/15hp Chinese OHV, Stage 2/3

As step up from the Stage 1, this kit is designed to improve the power for the GX340s and GX390s along with improving the durability.

Our Price: $449.99
Hop Up Kit - GX340 - GX390, 420 Predators, and 13/15hp Chinese OHV, Stage 4 Hop Up Kit - GX340 - GX390, 420 Predators, and 13/15hp Chinese OHV, Stage 4

The 3 kit starts with package similar to that of the stage 2 kit but adds a Ported and Milled Head with stainless, stainless valves, stud kit, & HD valve train components.

Includes

  • Race/Open Air Filter & Adapter,
  • Choice of Carbs
  • Choice of Cams
  • Ported Head, Milled .100" (Chinese OHV)
  • Stainless valves
  • Aluminum Retainers & Split Keepers
  • Chrome Moly Pushrods
  • Single or Dual Springs
  • 8 degree Timing Key,
  • Billet Rod +(.040 longer)
  • Carb, Head, & Case gaskets
  • Stud Kit
  • Roller Tip 1.2 Rocker Arms (Optional Aluminum Roller Rockers)
  • Optional Header/Exhaust
  • Optional Aluminum Flywheel

Picture for reference only and may show optional parts. See above description for actual content.
Header not included unless specified.

Due to head work required, allow 1 week to ship.

Note: Use of the Choke Bracket requires use of a stock Honda (or Chinese OHV) "Air Filter to Carb Gasket". This is not included in the kit. You can use the one that came with the motor, or can purchase one at
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Filter should be sprayed with K&N type oil, especially in dirt applications. Oil not included click here

These kits are intended for experienced engine builders. Some clearancing, fitment, or other engine building "tricks" may be needed.

Billet Aluminum flywheel recommended. Stock flywheels, esp "Clone" are prone to failure and very DANGEROUS

Note: UT2s series Hondas (2012 & up) or later have a built in Rev Limiter in the coil and will require a new coil to exceed 4000 rpm. The UT2 coils (4 wire) can only be used with stock flywheels.
If using a Billet Flywheel, you must run a UT1 style coil (single wire).

13/15 Chinese Engines (414, 420, 460) usually have UT1 style coils already. However some Lifans and 420s have a digital ignition and will need a Honda UT1 coil to run t he billet flywheel.

Our Price: $918.99