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Hop Up Kit - GX340 - GX390, 420 Predators, and 13/15hp OHV, Stage 4
 Hop Up Kit - GX340 - GX390, 420 Predators, and 13/15hp OHV, Stage 4

Our Price: $1,012.00

Stock Status:In Stock
Part #: STAGE4KIT390

Select Carburator

None (Customer to supply carb)
34mm Round Slide Mikuni - Gas [+$171]
34mm Flat Slide Mikuni - Gas [+$210]
33 Mikuni Pumper - Gas [+$315]
33 Mikuni Pumper - Methanol [+$377]
Select Flywheel

No Flywheel
Add Aluminum Flywheel - Recoil Start [+$166]
Add Aluminum Flywheel - Electric Start [+$202]

Description -

The Stage 4 kit starts with package similar to that of the stage 3 but adds a Ported and Milled Head with stainless, stainless valves, stud kit, & HD valve train components. This kit allows up to 35+ HP out of a GX390


  • Fully ported and milled race head (genuine Honda Core)
  • High Torque Genuine Honda Core (The Best!!)
  • High Flow 36mm / 31mm Valves with lash caps
  • Dual Springs with titanium retainers
  • 307 Race Cam
  • Black Venom Aluminum Roller Rockers
  • Valve Cover Spacer
  • Chrome Moly Pushrods
  • Choice of Carbs (or use your own)
  • 88mm Forged Flat Top Piston with rings
  • Billet Rod +.040
  • Offset Timing Key
  • Carb, Insulator, Head, & Case gaskets
  • ARP Bolt Kit

This kit only fits 389cc (88mm) Engines.

Picture for reference only. See above description for actual content.

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

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 REQUIRED

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 the billet flywheel .

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