Honda GX50 Rules   Print  


Honda Performance Development

GXH50 Class Information


The intent of the class is to provide a low cost, simple and reliable engine package for beginning Kid Karters to utilize. The engine must be run as produced. No deviation from the “as produced” engine is allowed. All components must remain OEM unless otherwise specified. No addition or substitution of components.


General Rules:


           1. Engine: Honda GXH50 as supplied by Honda Performance development.

a.       Engine seal: As installed by HPD.  If seal damaged, missing or disturbed in any way the entrant will be disqualified.

b.      Carburetor: KEIHIN BF32E

·         The only allowed changes to the carburetor are main jet changes. Any other change or modification is not permitted.

·         Throttle plate: # 140 as manufactured with sharp edges.  Must retain stock screw.

·         Main nozzle: Minimum length 1.140”

1.       Through hole: .055” No go

2.       Two holes at bottom, 180° apart .028” No go

3.       Eight holes above bottom band 90° apart .020” No go

4.       Four holes at top 90° apart .020” No go

·         Float: F3

·         Main Jet 52S:Go .48mm; No-go .50mm

·         Maximum venturi size (no?go): 15mm

·         All jets must be TIGHT.  Loose jets will be disqualified.

c.       Throttle linkage must be as supplied by HPD.

d.      Air Filter: Must remain stock, with stock foam insert.No external modifications of any type.

e.      Spark plug: NGK CR5HSB or Denso U16FSR-UB

f.        Kill switch:  Stock switch must remain connected.  An additional switch may be installed in reach of the driver.

g.       Oil: SAE 10W-30 or SAE 30 only. Hondaline oil recommended. No exotic oils such as those containing “combustion enhancers”.  Tech on oil using a refractometer is encouraged.

h.      HPD clutch cover with chain cover strap.  (What is status of this)

i.         Clutch: HPD supplied. No modifications allowed.

j.        Gearing:  16:89

k.       Exhaust: As supplied, modification or repair not allowed. Cracked or broken exhausts will be disqualified.

l.         No additional decals or other signage allowed on engine except for Honda or Honda Racing HPD.


2. Engine Mount pattern: 112mm X 54mm



            ·    Minimum wheelbase 29” (737 mm), maximum 31 1/2” (800 mm).

            ·    Overall Maximum width 42” (1067 mm) Minimum 39” (991 mm).


Tires: (4) 460 (450) X 5 as specified by series.

Wheels/tires: Rear overall width 130 -140mm Rear tire circumference: 33.00” min. 33.75” max.

Bodywork: CIK, FIK or IKF/WKA style allowed. Must include: front fairing, nose, side pods and full rear protection.

Front bumper: (nose) maximum width 40” (1016mm).  May not extend beyond front tires.

Front fairing:  Maximum width 9”.

Rear protection/bumper: CIK, FIK or IKF/WKA style allowed. Under no conditions may the rear protection extend beyond the plane of the rear tires.


Chest protection: All drivers in this class are required to wear a chest protector with SFI Section 20.1 Certificationduring any on?track session. Failure to comply may result in disqualification.


All entrants are subject to technical inspection.


Claiming: any competitor may claim an engine entered in the event subject to the following conditions:

       ·         Claimant must be entered in the race and have participated in at least two events in the class during the calendar year.

       ·         Claimed engine must have cleared Technical Inspection for the event.

       ·         Claimant must provide certified funds or cash in the amount of

$1000.00 US$.

       ·         Claimed engine will be delivered to the Claimant under the supervision of the event Technical Director and Race Director at the end of the event.

       ·         Claimed engine will be complete as supplied by HPD.

·         Failure to deliver the claimed engine will result in forfeiture of all Awards for the series.

       ·         HPD or their designate, reserves the right to claim any engine under this program.


 Additional technical inspection:


             1. External visual check of engine for required components: Pipe and muffler, shrouds and sheet metal, oil level sensor (this can be observed from outside).


A.      Blocking Air Flow to the engine: Only factory heat shield is legal. No device may be used that will/or appear that it may impede airflow into the engine cooling system. This may require that the engine be run at a speed above idle by the tech personnel at the scale after the car has qualified or raced.

B.      Engine should be at ambient temperature when presented to Pre-Grid.


    2.       Remove Carburetor:

             A. Only Stock Honda insulator gasket between black plastic insulator and head. Air passagway in insulator will not be altered in any way.

1. Insulator thickness: .277” +/- .001”.  Hole is rough edged and is “as molded”

2. Insulator (head side) gasket thickness: 0.019” maximum.

3. Insulator (carb side) gasket thickness: 0.022” maximum.

B. Check for any alterations or worn parts that would allow additional air into engine: holes, slots, perforations, spacers, loose bolts, warped flanges etc.


Valve Springs:

Valve springs will be stock Honda springs and will not be altered in any way.

A. Wire diameter: 0.064" maximum

B. Outside diameter of spring: 0.588" maximum

C. Number of total coils: 6

D. Spring pressure: TBD LBS maximum at TBD

E. stacked length will be: TBD maximum

Rocker Arms – Push Rods – Studs:

Rocker arms will be stock Honda and will not be altered in any way. Rocker arm studs will be stock Honda. They or their mounting position may not be altered in any manner. No heli-coiling of mounting holes. No bending of studs. Push rods will be stock Honda and will not be altered in any way.

A.      Push rod length is 2.774”  +/-.002”









Updated 29 Jan 2014 11:16
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