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Stage 4 Honda GX390

Stage 4 Honda GX390

Choose your options:
390/420 Carb Option(required):
390/420 Flywheel(optional):
390/420 Header & Exhaust(required):
390/420 Ignition Coil(required):
Product Code: STAGE4KIT390
Stage 4 Hop Up Kit for GX390
The Stage 4 kit starts with a package similar to that of the Stage 3, but adds a ported and milled head with stainless valves, a stud kit, and heavy duty valve train components. Allows up to 35+ HP out of a GX390.

Kit Includes:
  • Fully Ported and Milled Race Head
  • 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" Longer)
  • Aluminum Flywheel Recoil Start
  • Offset Timing Key
  • Carb, Insulator, Head, and Case Gaskets
  • ARP Bolt Kit

*Note: This kit only fits 389cc (88mm) engines. Kit is intended for experienced engine builders. Some clearancing, fitment, or other engine building "tricks" may be needed. Picture is for reference only. See above description for actual content. Filter should be sprayed with K&N type oil, especially in dirt applications. Oil not included - click here. Billet aluminum flywheel required.

UT2 series Hondas (2012 & up) or later have a built-in rev limiter in the coil and will require a new coil to exceed 4000rpm. 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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