Home > Engine Parts > Performance Engine Parts > Hop Up Kits > GX390, GX340, 420 Predator, & 11hp up Chinese OHV
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Champion Shaft Mounted Big Block Rocker Arm 1:1 BIG BLOCK GX340 - GX390, 420 Predators, and 13/15hp OHV, Stage 1 Stage 2 GX340 to GX390, 420 Predator, & 13/15hp OHV
Shaft Mounted 1:1 Ratio Rocker Arms for GX390, 420 OHV, and 460cc
  • These are the famous "Champion" HD shaft rockers for GX390 and 420 OHV engines. They are arguably the best bang for your buck when it comes to valve train stability.
  • A shaft rocker eliminates the need for a guide plate and prevents the rocker arms from walking side to side. Further, they have considerably more rigidity than stud rockers, so they rarely need adjustment once set.
  • Studs and nuts included (Studs may require tools to install = to tight to turn by hand)
  • Fits GX390 and 420 OHV engines. Will not fit GX270s.

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

Stage 1 Kit includes

· Race/Open Air Filter & Adapter,

· Main Jet for Application (see Notes)

· Pilot Jet

· Choke Hold Down Bracket

· Choice Of Header/Exhaust

Picture for reference only and may show optional parts. See above description for actual content.

Filter should be sprayed with K&N type oil, especially in dirt applications. Oil not included

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

Note: UT2s series Hondas (2012 & up) have Rev Limited coils and will require a new coil to exceed 4000 rpm. The UT2 coils (4 wire) can only be used with stock flywheels or 6693 ARC flywheels. If using any other Flywheels, you must run a UT1 style coil (single wire). Most 390 “clone”, 420s, and 460s have UT1 style coils already (However some Lifans and 420s have a rev-limited digital ignition)

The difference in the Kits is the main jet. We recommend you check the check your STOCK main . If stock main is a :

· #92 thru 97, use a UT1 kit,

· #98 thru #102 use a Hemi Kit’

· >102, Use a UT2 kit

Manufacturers have been know to use different jets on the same models. So it is important to know the stock jet size

Stage 2 Hop Up Kit for GX340-GX390, 420 Predator, and 13/15hp OHV Engines
As a step up from the Stage 1, this kit is designed to improve the power and durability of GX340s and GX390s.

Includes:
  • Race/Open Air Filter & Adapter
  • 23.5mm Honda Race Carb (Bored)
  • Heavy Duty Valve Springs
  • Aluminum Flywheel - Recoil Start
  • Offset Timing Key
  • Twister Camshaft
  • Carb and Side Cover Gaskets
  • Optional Header/Exhaust
  • Optional Aluminum Flywheel
  • Optional Valve Cover Gasket for Hemis
*Note: Use of the choke bracket requires use of a stock Honda (or Chines OHV) "Air Filter-to-Carb" gasket. This is not included in the kit. You can use the one that came with the motor, or you can purchase one from us here.

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.

Header not included unless specified.

Filter should be sprayed with a K&N type oil, especially for dirt applications. Oil not included - click here.

Picture is for reference only and may show optional parts. See above description for actual content.

Warning: Billet aluminum flywheel recommended. Stock flywheels, especially "clones" are prone to failure and are very dangerous!
stage 3 Kit 420 Hemi Predator Stage 3 Kit GX390 & 13/15hp OHV Stage 4 Kit 420 Hemi
Stage 4 Kit 420 Hemi
Our Price: $1,125.99
Stage 3 Hop Up Kit for 420 Hemi Predators
A step up from our Stage 2 kit, this will further empower the 420, producing up to 20+ HP!
*Note* Unlike the Stage 2, this kit will not work with OHVs! For a GX390 & 13/15hp OHV Stage 3 kit, click here.

Kit Includes:
  • Race/Open Air Filter & Adapter
  • Heavy Duty Valve Springs
  • Aluminum Flywheel Recoil Start
  • Offset Timing Key
  • 280 Lift Cam
  • Billet Rod +.040" Longer
  • Carb, Side Cover, and Valve Cover Gaskets
  • Optional Header/Exhaust
  • Optional Aluminum Flywheel

Pictures are for reference only and may show optional parts. Please see above description for actual contents.
Stage 3 Hop Up Kit for GX390 and 13/15HP OHV
A step up from our Stage 2 kit, this is designed to wake up GX390s, allowing 20+ HP!

Kit Includes:
  • Race/Open Air Filter & Adapter
  • Heavy Duty Valve Springs
  • Aluminum Flywheel Recoil Start
  • Offset Timing Key
  • 280 Lift Camshaft
  • Reinforced Rocker Arms
  • Billet Rod (+.040 Longer)
  • Carb and Side Cover Gaskets
  • Optional Header/Exhaust
  • Optional Aluminum Flywheel

*Note:
Use of the choke bracket requires 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 you may purchase one here.

Billet aluminum flywheel recommended. Stock flywheels, especially "clones", are prone to failure and are very dangerous.

UT2 series Hondas (2012 & up) and 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, and 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.

Picture is for reference only and may show optional parts. See above description for actual content.
Stage 4 Hop Up Kit for 420 Hemi
The Stage 4 kit starts with a package similar to that of the Stage 3, but adds a ported and milled hemi head with stainless valves, a stud kit, and heavy duty valve train components. This kit allows up to 35+ HP out of a 420!

Kit Includes:
  • Fully Ported and Milled HEMI Race Head
  • High Flow 40mm / 34mm Valves with Lash Caps
  • Dual Springs with Titanium Retainers
  • 307 Race Cam
  • Shaft Mounted Roller Rockers
  • Chrome Moly Pushrods
  • Choice of Carbs (Or use your own)
  • Forged Flat-Top Piston with Rings
  • Billet Rod (+.040" Longer)
  • Aluminum Flywheel Recoil Start
  • Offset Timing Key
  • Carb, Insulator, Head, Valve Cover, and Case Gaskets
  • ARP Bolt Kit

*Note: Picture is for reference only and may show optional parts. See above description for actual content. 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.
Stage 4 Honda GX390 Stage 4 Kit 420 Predator OHV & 13/15hp Clone
Stage 4 Honda GX390
Our Price: $1,205.99
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.
Stage 4 Hop Up Kit for 420 Predator OHVs & 13/15hp Clones
This kit is similar to our 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 420 engine. This kit is for OHV engines and will not fit Hemis.

Kit Includes:
  • 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)
  • 90mm 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 414 & 420cc (90mm) non-hemi engines. Filter should be sprayed with K&N type oil, especially in dirt applications. Oil not included - click here. Billet aluminum flywheel REQUIRED. These kits are intended for experienced engine builders. Some clearancing, fitment, or other engine building "tricks" may be needed. Picture for reference only. See above description for actual content.