Kart Classing – Cumberland Motor Club

Will your Kart pass Tech inspection? Click here.

After you read these pages, if you still have questions, contact Braelan Creswell, The CMC Kart Chair.

Note: A competitor may petition to move up ONE class to the club’s kart chair and club President. For example an 11 year old competitor may ask to move up from Formula Junior 1 to Formula Junior 2. The competitor must have proven driving ability and control.

Kart Classification

Formula Junior 1 (FJ1) Competitors age 8-11 4 cycle Box Stock 5.5 HP or Blueprinted WKA Briggs with restrictor. Rotax Micro Max. Electric karts up to 3.7kW
Formula Junior 2 (FJ2) Competitors age 11-18 4 cycle Box Stock 5.5 HP Maximum or Blueprinted WKA Briggs with restrictor. Electric karts up to 3.7kW
Formula Junior 3 (FJ3) Competitors age 8-18 Blueprinted WKA Briggs, Briggs World Formula with restrictor or Piston Port 2 stroke up to 100cc with restrictor, or Comer K-80 and Cadet Chassis. Electric karts up to 7.4kW
Formula Junior 4 (FJ4) Competitors age 8-18 Briggs World Formula or Piston Port 2 stroke up to 100cc with 4 hole can muffler. Electric karts up to 11.1kW
Formula Senior 2 (FS2) All competitors running 4 cycle Box Stock 5.5 HP manufacturer’s rating.
Formula Senior 3 (FS3) All competitors running 4 cycle WKA Briggs Flathead, Briggs World Formula with restrictor or Piston Port 2 stroke up to 100cc with restrictor, or Comer K-80 and Cadet Chassis
Formula Senior 4 (FS4) Briggs World Formula or Piston Port 2 stroke up to 100cc with 4 hole can muffler
Formula Senior Super (FSS) All competitors running other engine configurations
Formula 125 (KM) (as per current SCCA regs.)

Tires, Restrictor Plates, Mufflers, Personal Equipment

General

Kill switches are strongly recommended for all classes.
All 4 cycle motors must run an RLV-B91 WKA approved silencer in an unaltered state or a stock factory muffler.
Exhaust headers including silencer must extend beyond the gas tank. Note: This may preclude the use of a standard factory muffler without a header!
Minimum kart dry weight with no driver or fuel, with engine, is 85 pounds.
Approved fuels for 4 cycle motors are gasoline and methanol. (Note that there are class specific exceptions)
Any clutch system or torque converter may be used. (Note that there are class specific exceptions for World Formula and Comer K-80 engines)

Tires

ALL Junior Kart classes must run MG Red tires (SH) or equivalent hardness tires.
Senior Kart classes may run MG Red (SH) or MG Yellow (SM) or equivalent hardness tires.
Kart Modified (F125) tires are Non-Tech, any tire within size restrictions is allowed.
Rain tires are Non-Tech for all classes

Competitors 8 to 11 years old – (Formula Junior 1)

Briggs 4 Cycle WKA motors must run WKA Purple .425″ restrictor plate.
Box Stock gasoline motors will run with WKA Gold .575″ restrictor plate.
Competitors from this age group may be asked to install a smaller restrictor plate if they have demonstrated unsafe driving habits anywhere on the event site.
FJ3 competitors with specifications as listed below for specific engine/chassis combinations

Novice Competitors from 12 to 15 years old – (Formula Junior 2)

Briggs 4 Cycle WKA motors must run WKA .575″ restrictor plates.
Box Stock 5.5 HP maximum rated gasoline motors can run unrestricted.
Competitors from this age group may be asked to install a smaller restrictor plate if they have demonstrated unsafe driving habits anywhere on the event site.
FJ3 competitors with specifications as listed below for specific engine/chassis combinations
FJ4 competitors with specifications as listed below for specific engines

Competitors 16 years and older – (Formula Senior)

Briggs WKA motors can be run unrestricted.
FS2 competitors running 4 cycle Box Stock Engines with up to 5.5 HP manufacturer’s rating.
FS3 competitors with specifications as listed below for specific engine/chassis combinations
FS4 competitors with specifications as listed below for specific engines
FSS competitors with other approved engines

Personal Equipment – (ALL COMPETITORS)

Helmet must be full faced. Shield must be attached to helmet or goggles designed for motorsports must be worn. The helmet must meet Snell M90 / SA90 or newer.
An abrasion resistant suit specifically designed for Karting is strongly recommended. At the very least heavy, abrasion resistant jacket of denim, nylon, leather or vinyl and full length pants must be worn.
Long hair must remain inside helmet. A balaclava or headsock is strongly suggested to prevent it from extending outside of the helmet edges. Red flag will be thrown for flying hair.
Collar type neck braces designed for motorsports are mandatory.
Shoes must be leather or canvas, feet must be fully enclosed, socks are required.
Abrasion resistant kevlar gloves are highly recommended. Heavy gloves of abrasion resistant material are mandatory.

4 Cycle Gasoline Engine Specifications (Box Stock)

AIR FILTER

An air filter is required and must be installed in a safe manner. Air Filter may not be used as a ram air device and must filter from all areas as raced. No open areas are allowed. Filter adapter to carburetor may not be funneled or tapered. Adapter may have a rolled edge not to exceed .250″ from top. Maximum thickness of adapter from carburetor mating area to top of adapter is .250″, top of adapter must be flat. One gasket may be used with a maximum .075″ thickness. Adapter may not be run without air filter.

GOVERNOR ASSEMBLY

May be removed in their entirety. Governor shaft in block or side cover may be broken off or removed and plugged.

STARTER

New style recoil starter (Briggs) may be left intact. If new style recoil is removed, starter cup must be removed. Old style recoil must be removed. Use of external (not attached to motor) electric starters are allowed.

EXHAUST SYSTEM

Header may not enter into exhaust port so as to alter port configuration. Pipe must be of fixed configuration, no “slippy pipe” designs. Loss of exhaust system during competition will result in a DNF for that run only.

FUEL TANK

Tank repair kit may be used in pickup cup (Briggs). No overflow tubes or cap splash shields.
Gas caps may be replaced with self priming plunger type as long as vent hole system similar to stock is retained.
Gasoline is used as fuel.
Properly mounted karting style steering column tanks may be used in place of “stock” style steel tank
Vacuum operated fuel pump may be added in case of center mounted tank.

BORE & STROKE

Maximum over bore allowed is .040″. Angle boring or machining of grooves or patterns in the bore is prohibited. Stock stroke +/-.010 for wear, stroke is checked from BDC to TDC. Minimum crankshaft diameter is .010 below stock specification.

MISC

Box stock means right out of the factory box and NO MODIFICATIONS are allowed. If it does not say you can do it in these rules, then you cannot. All motors are to remain box stock with the exception of what has been stated in these rules. These rules will be strictly enforced for the sake of fair competition .Note: Gas caps may be replaced with self priming plunger type as long as vent hole system similar to stock is retained.

4 Cycle WKA Engine Specifications

AIR FILTER

An air filter is required and must be installed in a safe manner. Air Filter may not be used as a ram air device and must filter from all areas as raced. No open areas are allowed. Filter adapter to carburetor may not be funneled or tapered. Adapter may have a rolled edge not to exceed .250″ from top. Maximum thickness of adapter from carburetor mating area to top of adapter is .250″, top of adapter must be flat. One gasket may be used with a maximum .075″ thickness. Adapter may not be run without air filter.

BLOCK

Must be as produced with no alterations or reworking. Block repairs from broken rods or cracked lifter area etc. are permitted providing that repair does not constitute a functional modification of the original block. Blocks may be clearanced on the bottom of the cylinder to provide clearance for all approved connecting rods (see connecting rod section for list of approved rods). Block may NOT be machined on intake or exhaust port gasket mating surface. No bushings are allowed except as listed in this engine section. A DU bearing may be installed in a conventional block on the flywheel side. An extra 1/8″ oil hole may be drilled on the flywheel side at the crankshaft bushing of the block to aid in crankshaft oiling. Sleeving of the cylinder block is permitted. Regular ferrous sleeves only, no coatings or plating allowed. The repair of one coil mounting post is allowed as long as the remaining post is unaltered. Lifter bore welding for reinforcement or breakage is allowed. Use of a bushing guide to reinforce the lifter bore area is allowed. Chamfering the bottom of the lifter bore is allowed for clearance purposes only. Chamfer to be 45 degrees and a maximum width of .040″. Intake port is subject to .880″ no-go gage. Exhaust port is measured with a 1.005″ no-go gage. Material cannot be added to ports. No grinding is allowed under valve seats. No holes in ports, if port is pin-punched, resulting risers may not prevent insertion of no-go gage.

BREATHER VALVE

Must be unaltered from factory and functional. Foam and original grommet must be in place. Two gaskets are allowed.

BOLTS

Any bolt utilized to attach sheetmetal and shrouding may be replaced with a larger diameter with the exception of the sheetmetal held in place with head bolts. Any other bolt may be replaced with the exception of Rod and Head bolts as long as the replacements are the same diameter. See connecting rod section for more clarification. Any stock head bolt may be used; all eight bolts must be present. Factory headbolts with stud extensions on top are permitted.

BORE & STROKE

Stock cylinder bore is 2.5625″. Maximum over bore allowed is .040″. Angle boring or machining of grooves or patterns in the bore is prohibited. Stock stroke is 2.4370″ +/-.010 for wear, stroke is checked from BDC to TDC. Minimum crankshaft diameter is .990″.

CAMSHAFT

Only WKA approved camshaft with original alignment is allowed. Slight grinding allowed for clearance when using approved after market connecting rods.

Camshaft profile limits measured at zero valve lash:

Lift	Degrees	Degrees
	Exhaust	Intake
.050″	38 BBDC to 33°BBDC	7°BTDC to 0°TDC
.100″	21 BBDC to 16 BBDC	10 ATDC to 17 ATDC
.150″	2 BBDC to 3 ABDC	29 ATDC to 38 ATDC
.200″	21 ABDC to 31 ABDC	55 ATDC to 64 ATDC
	Max Lift is .233″	Max Lift is .233″
.200″	76 BTDC to 65 BTDC	43 BBDC to 33 BBDC
.150″	48 BTDC to 40 BTDC	13 BBDC to 6 BBDC
.100″	28 BTDC to 21 BTDC	6 ABDC to 13 ABDC
.050″	10 BTDC to 4 BTDC	23 ABDC to 31 ABDC

EZ-Spin Start: 45 to 60 ABDC
EZ-Spin Lift Base: .013″ min. width, .019″ max. width, .001″ max. drop during 30 duration time.

CARBURETOR

Only stock factory carburetor is allowed. They may be blueprinted as per current WKA specs.

CONNECTING ROD

The following rods are approved for use: Stock Briggs & Stratton 5HP, As cast, Raptor II rod and dipper or old style rod with after market dipper is legal. Must be as cast. The following approved after market rods and their respective manufacturer’s original connecting rod bolts and/or nuts are allowed for increased engine durability. Horstman PN’s 4951, 4981 Holoway PN HR-3.875 Burris PN’s BMC-25400, -26500 A.R.C. 6350 No lightening is allowed. Slight grinding allowed on backside of rod for camshaft or lifter clearance. Rod length 3.1283″ +/-.005″

CYLINDER HEAD

Stock 5HP head as shipped from Briggs and Stratton. Machining of gasket surface for sealing purposes and head bolt bosses for flatness is allowed. No other machining is allowed. Minimum head gasket thickness .043″. Three internal cylinder head surface measurements as measured from the gasket surface to area above piston .011″, .408″in spark plug area, .300″ in area above valves. Carbon buildup that cannot be cleaned with a dry cloth is considered part of head surface.

CRANKSHAFT

Stock factory crankshaft only. No lightening, polishing or addition of metal allowed. Hardening is allowed to reduce journal wear. Crankshaft may be clearanced to a minimum of .775″ to allow easier removal of the bearing. The power takeoff journal of a sleeve style bearing crank may be machined to allow its use in a ball bearing style block. Offset cranks are illegal.

PISTON / DECK

The piston may not protrude more than .015″ above deck surface at TDC.

FLYWHEEL

Stock 5HP only. No painting or coating. No machining. Chipped fins due to poor casting acceptable, completely broken fins are not. Minimum weight 6 lbs. Any screen or guard allowed that fully covers the flywheel. Screen must be bolted to blower housing.

GOVERNOR ASSEMBLY

May be removed in their entirety. Governor shaft in block or side cover may be broken off or removed and plugged.

IGNITION

Briggs & Stratton factory stock coils only. Must be used in unaltered form, no slotting of mounting holes or modifications to mounting bolts are allowed. Coil air vane must remain intact and unaltered, coil must retard. Plug wire resistance 2000 ohm minimum, 5000 ohm maximum. New style Briggs composite ignition allowed, there must be resistance to ground from the plug wire. Plug wire connector must be stock factory type, rubber boot is legal.

PISTON, PIN & RINGS

The following pistons are approved for use. The following approved after market pistons are allowed for increased engine durability. Briggs & Stratton 5HP stock factory production Wiseco PN 1993P – Top may be machined to .937″ minimum from top of wrist pin hole. Burris PN BMC 258 Measurement from piston top to wrist pin hole is .937″ minimum. Minimum length 1.869″. Pin hole may not be relocated or altered. Deck above top ring may not be altered, no machining on piston except as noted above. Pin can not be modified, max ID .290″, min OD .490″. All 3 piston rings must be used. Top ring, if beveled, may have either a beveled or chamfered inner face or two beveled or chamfered areas on outside face, must remain as manufactured. Two top rings minimum width .105″. Second ring may only have an external circumference relief area. Oil ring minimum width .085″. Groove with .083″ min width, and all 6 oil relief slots must be present. Ends of rings must remain flat. Ring end gaps cannot exceed .500″. Rings must conform to factory specifications, stock configuration and be Briggs & Stratton factory approved parts.

FUEL TANK

Tank may be altered for tire clearance. Tank repair kit may be used in pickup cup. No overflow tubes or cap splash shields.
Gas caps may be replaced with self priming plunger type as long as vent hole system similar to stock is retained.
Methanol or Gasoline may be used as fuel.
Properly mounted karting style steering column tanks may be used in place of “stock” style steel tank
Vacuum operated fuel pump may be added in case of center mounted tank.

SHROUDS & COVERS

Shrouds and covers on engine must be intact and factory stock with NO modifications. Fixed screen may be added to shroud cool air intake area.

STARTER

New style recoil started may be left intact. If new style recoil is removed, starter cup must be removed. Old style recoil must be removed. Use of external (not attached to motor) electric starters are allowed.

VALVES

Stock valves only. No industrial stellite valves allowed. One angle only on seats and valves. Intake angle 30 , exhaust angle 45 . Minimum intake valve diameter 1.115″, intake seat 1.004 minimum diameter. Exhaust valve minimum diameter .990″, minimum seat diameter .880″. No polishing, knife edging, lightening or refacing allowed. No material may be removed from valve stem, i.e. no linear grooves, or crosshatching etc. Stock Briggs & Stratton valve seats must be used and can be replaced. Stock specification and Briggs & Stratton valve guides allowed. Stacking of stock guides is allowed.

VALVE SPRINGS & LIFTERS

WKA approved valve springs only. Max. Intake spring length 1.240″ with .087″ wire size. Max. Exhaust spring length is 1.410″ with min. .088 wire size. Exhaust spring must be used on exhaust valve and may be used on intake if desired. Springs must remain unaltered with the exception of metal removal from top of spring to allow spring to pass 1.410″ min length measurement. One Briggs & Stratton part number 23184 upper retainer may be used on each spring in unaltered form. Maximum lip thickness .058″. No extended or adjustable lifters allowed. Lifter head must be .982″ min. diameter. Back facing of upper surface of valve chamber to stabilize valve spring retainers and to prevent spring bind is legal.

EXHAUST SYSTEM

Header may not enter into exhaust port so as to alter port configuration. Pipe must be of fixed configuration, no “slippy pipe” designs. Loss of exhaust system during competition will result in a DNF for that run only.

MISC.

If it does not say you can do it in these rules, then you cannot. All motors are to remain stock with the exception of what has been stated in the current WKA rules. These rules will be strictly enforced for the sake of fair competition.

Briggs World Formula Engine Specifications

FJ3 and FS3

As homologated except it is permissible to use type 35 size chain vs stock type 219.
Gasoline only
Restrictor or throttle stop as per current SCCA regulations in KJ3 and KS3
Restrictor Details: Contact Eric Nelson, Seventh Gear, work phone: 888-717-7223; http://www.seventh-gear.com
E-Mail: (mailto:sales@seventh-gear.com) ;
US Mail Address: 125 Santa Clara St., Unit 6, Arcadia, CA 91006
Muffler must be unmodified RLV muffler for World Formula Engine (Canadian, CIK, WKA or IKF approved)
Any configuration allowed per current SCCA Solo II regulations to run in FJB

FJ4 and FS4

As homologated except it is permissible to use type 35 size chain vs stock type 219.
Gasoline only
Muffler must be unmodified RLV muffler for World Formula Engine (Canadian, CIK, WKA or IKF approved)
Any configuration allowed per current SCCA Solo II regulations to run in FJA

Piston Port 2 stroke up to 100cc Engine Specifications

FJ3 and FS3

Piston Port 2 stroke up to 100cc
Walbro WA55b or HPV1 with WA55b manifold (Yamaha KT100 only) with RLV SSX-V exhaust or
Walbro WB3A carburetor and .600 restrictor plate with RLV SSX-V exhaust
If the pipe has a hole for EGT sensor, EGT sensor probe must be in place

FJ4 and FS4

Piston Port 2 stroke up to 100cc
Gasoline and oil premix only
Walbro WB3A carburetor (Yamaha KT100 only) and RLV SSX-V exhaust (4 hole)

Comer K-80 Specifications

FJ3 and FS3 only

Comer K-80 exhaust and clutch as supplied by manufacturer
Gasoline and oil premix only
Kart Chassis: Cadet Chassis (overal length 69″, wheelbase 35″ min, 38″ max.); to be used only with this engine package

Electric Kart Specifications

All Electric Karts:

All (reasonable) battery chemistries are allowed (not sure why you would have a Mercury oxide battery but please don’t bring one) , however, the proper battery protection system must be utilized to match the battery.
MUST have shielding on the battery to prevent puncture, may be open on top for ventilation + hot swap.
Batteries MUST be adequately secured such that they may not move during any on course incident.
Drive systems may utilize direct drive, chain, or belt. In the case of a chain or belt, a guard must be installed to prevent injury from a broken chain or belt.
Power wires must be routed and secured in a way that they may not chafe or come into contact with moving components. They must also be adequately insulated + sized for the utilized voltage + current.
Motors must drive the rear wheels, and must be mounted next to, or behind the driver.

FJ1 and FS2

3.7kW motor max power output (5hp)

FJ3

7.4kW motor max power output (10hp)

FJ4

11.1kW motor max power output (15hp)

FSS

No hard power limit, though must not be faster than a 125 KM shifter kart ~37kW, 50hp.
Karts with motors over 11.1kW (15hp) must have front + rear brakes.

Super Stock Engine Specifications

General

This class is intended to encompass all karts modified beyond the WKA “blueprinted” flathead class guidelines. Various two and 4 stroke, single cylinder engine types and sizes are expected. This includes Yamaha KT100 with tuned exhaust, Rotax, Leopard, HPV, IAME, ATK, Tecumseh Star etc… This will NOT include large motorcycle or snowmobile engines.
Up to 250cc, single cylinder, 4 stroke engines with or without gearbox will be allowed to participate in this class provided they meet the safety regulations and restrictions otherwise applicable to the Super Stock Class, in addition to the K Modified (KM) Class. Karts that prove to be faster than a 125cc KM shifter kart will not be allowed to participate.
Experimental electric drivetrains will run in this classification. Electric karts will require extensive kart safety inspection prior to approval.
There are NO specific engine modification limits!

EXHAUST SYSTEM

Loss of exhaust system during competition will result in a DNF for that run only.

MISC.

Any racing kart and motor combination that is deemed safe by the CMC Autocross Chair, Safety Chair, and Kart Chair will be allowed to run in this class. No kart will be allowed to run if it is felt to be faster than a legal KM (125 shifter) Kart.
Exclusions: Please contact CMC for review of your kart prior to event attendance if you have questions.
- Airxo Rotary, All Configurations
- Mega-R01

Revision 11 Revised 5/31/23