Late summer, Jerry Welch, Welch Performance, asked us to help create a rule set for a 212cc Honda-Clone Based Limited Modified Class for the 2024 Big O and other National & Local Races. The limited modified has been a popular class for both flathead and Briggs Animals, but the growing popularity of the Tillotson and other clone engines for modified racing has gained a lot of attention. Unfortunately, Jerry would unexpectedly pass in the fall. We have been working with Dynocams and techs at NKA and WKA in hopes of adding this class to their rule books.
Welch 212cc Limited Modified Kart Classes
A. Crankcase Assembly
A1. Block
- Any Honda Clone(Ducar, Predator, Tillotson, Wildcat, BSP,) 70mm Block.
- 2.778 Cylinder Bore No-Go
- Billet Blocks are Prohibited
- Welding or epoxy repair is permitted on the block and side cover. Repair may not be a functional modification (performance enhancing, e.g., No reinforcements to the jug or fins) of the OEM part.
- Decking of the block is permitted. No pop-up of the piston is allowed.
- No Deck Extensions
- Deburring of excessive flash is allowed but not to alter OEM specification or appearance.
A2. Crankcase Side Cover
- Billet Side Covers and Pressure Control Valves are permitted
A3. Fasteners
- Non-tech unless otherwise stated, but must retain their original factory size & location. Heli-coils, studs, etc., allowed for repair purposes. Solid dowel pins are allowed. Washers allowed under head and crankcase bolts
A4. Gaskets & Sealer
- Gaskets must be in OEM configuration and are non-tech, and sealer may be applied unless otherwise specified.
- Head Gasket Non-Tech
A5. Bearings
- Crankshaft bearings must be the same dimensions as the OEM bearings. This includes inner and outer races as well as the balls and rollers. Metal or Ceramic bearings are permitted.
A6. Blower Housing Assembly
- Blower Housing must be present with Flywheel Cover
- Hand-held electric Starters are permitted
- 3rd Bearing Supports are permitted
B. Rotating Assembly
B1. Coatings & Polishing
- Coating, tumbling, and/or polishing of internal parts and head is prohibited unless otherwise stated
- Teflon/Coated Piston skirts are permitted. No Coating is allowed on the Piston Crown or Combustion Chamber
B2. Piston
- 70mm(2.756”)-70.50mm(2.776) Max Diameter
- Any Dish or Flat Top Piston(No Domes)
- No Piston Pop-Up
B3. Rod
- Non-Tech, Aluminum Billet rods are permitted. Steel & Titanium Rods are Prohibited
B4. Crankshaft
- Standard OEM item with a stock stroke length of 55mm or 2.165” (+/- .007”).
B5. Ignition Coil
- Ignition coil must be OEM for all classes. (NO CDI, Digitally control Ignitions)
- Timing is non-tech.
B6. Flywheel
- Approved Flywheels:
• ARC-6619 flywheel ™
• ARC-6618 flywheel ™
• ARC-6689 flywheel ™
• Dyno PVL 211-900 flywheel ™
• EC SK100 Rev Wheel™
• EC SK200 Rev Wheel™
• King Billet Aluminum Slipstream Flywheel ™
- The flywheel key may be altered and is non-tech; the key is not required to be installed.
- Flywheels must have a minimum weight of 3.3 pounds.
- Modification or removal of fins is prohibited.
C. Cylinder Head
C1. Approved Cylinder Heads
Any Factory 22cc Open Chamber Non-Hemi cast heads will be allowed. Any other heads need to be approved before competition.
- Heads that are Prohibited:
• Hemi (Ducar, Predator, Wildcat, etc)
• Small Chamber (18cc, 14cc, 12cc)
• Honda GX160 T1
• Wildcat WC946
• EC Evolution
• Gage CNC Cast Heads
• DTV Shredder Round Intake Port
C2. Porting
- Porting, grinding, or matching to the ports or combustion chamber is permitted.
C3. Minimum Combustion Chamber Volume
- Measure the total length between the valve seats in the combustion chamber and the top of the piston. Chamber Depth + Head Gasket Thickness + Piston Depth
This will be done after the event and when the engine has cooled to a reasonable temperature. A head gasket is required, but the thickness is non-tech and can be copper, steel, aluminum or composite(fire ring). Multiple head gaskets are allowed.
Minimum Depth .280”
- No Grinding or polishing of the combustion chamber.
- No angle milling of the head. The measurement taken from the gasket surface: depth check to combustion chamber floor cannot vary more than .005” in any direction.
C4. Valve Seats
- Valve Seat Angles - Non-Tech
- Intake Seat ID .977” Max Max
- Exhaust Seat ID .897” Max
C5. Valve Guide
- Valve Guide must be in the original location
- Valve Guide minimum length: 1.055”
- Stock Iron Guides Only
- Bronze and Non-Stock Materials are prohibited
C6. Valve Covers & Breathers
- Valve Spacer is permitted
- Billet Valve Covers are Permitted
- Valve Cover/Crankcase Vents and Breather must have lines to a catch can.
D. Camshaft & Valve Train
D1. Valves
- 5mm or 5.5mm Carbon(Stock) or Stainless Steel Valves Only (No Titanium, Inconel, etc.)
- Intake Valve Head OD 1.063”
- Exhaust Valve Head OD .984”
- Valve Length and Weight Non-Tech
D2. Rocker Arms
- 1:1 ratio rocker arms only - Stock Stamped, Gen1 & Gen2 Champion
- Rocker arms must be steel and are subject to magnetic tests.
- Rocker arms are allowed to be ground on valve stem location only, or on bottom of rocker arm to allow running lift to be compliant. Grinding on the sides of the rocker arm is prohibited. There are no minimum thickness checks.
D3. Valve Springs
- Non-Tech
D4. Valve Spring Retainers
- Billet Aluminum & Titanium are Permitted
- Lash Caps - Non-Tech
- Valve Seals - Non-Tech
D5. Push Rods
- 3/16 or 1/4 Chromoly Push Rods are Permitted
D6. Lifters
- Billet Lifters Permitted
- Length: 1.350”-1.390”
- Outside Diameter: .935” maximum
- Minimum Weight: 18 grams
D7. Camshaft
- Billet Cam Core is Permitted
Duration taken from pushrod: Intake and Exhaust duration of 248° degrees at .050 lift and 153° at .200” lift. Camshaft tolerances: +2 degrees with no minimum duration check
- Intake lift at pushrod is .310” Max. Intake lift at retainer .315 Max
- Exhaust lift at pushrod is .310”. Exhaust lift at retainer 315 Max.
- Running Lift will be checked as raced.
E. Carburetor & Fuel
E1. Carburetor
- Diaphragm with butterfly Carburetors ONLY (Tillotson HL & EC Billet Intimidator XR-25
Carburetors Only)
- Max Venturi .900” - .901” NO-GO
- Min Venturi .860 - .860” GO-Gauge
- Max Throttle Bore 1.00” - 1.001 NO-GO
E2. Fuel
- 100% Pure Methanol (No Additives)
- Floor-mounted fuel tanks are required. The OEM tank must be removed from the engine.
- Any pulse-type fuel pump permitted and can be pulsed from the intake, crankcase, side cover, or valve cover.
F. Exhaust System
F1. Exhaust System
The maximum length is 24 inches, measured through the inside of the pipe with a .250-wide tape measure. Remove the silencer and pull the tape measure tight. If any portion of the pipe's length is below 24 inches, it is legal.
- Complete Pipe & Silencer cannot extend past the rear bumper and must be totally contained inside the kart frame.
- Loop or Loop type pipes are prohibited.
- Gasket and/or silicone are allowed to seal the header pipe to the head.
- Pipe must be safety wired.
- Header Flange: maximum thickness .510”.
F2. Header
- Height must be 10 inches maximum from the top of the header flange.
- Header pipe wrap required from the header flange to the silencer. It must be overlapping, and no part of the header is showing.
The header must be braced. At the end of the race, the header and muffler must both be secure (tight)—this is grounds for disqualification.
- Ceramic coatings permitted on pipe only. Coatings on any other part of the exhaust are prohibited.
- Studs on exhaust may be replaced with regular threaded bolts of equal diameter and must be safety-wired.
F3. Muffler
- Silencer RLV B-91 series model 4106 is mandatory with all baffle plates on the inside and must be supplied by the manufacturer. Coating is prohibited.
- A clamped brace must support the silencer—no welding of brace to silencer or pipe. The silencer must be able to be removed for inspection.
- Silencers cannot be parallel to the ground. It must point towards the rear bumper or ground. The lowest part of the silencer can be a maximum of 9.0” above the mounting surface of the block.
G. Clutches
G1. Clutches
- Stamped steel or billet drum shoe-type clutches, disc clutches, and machined billet drums are approved.
- No CVT