5.0 h.p. Briggs & Stratton cool bore or I/C engine ONLY. Maximum displacement allowed is 12.97 C.I.

Boring of block is allowed to a maximum of +.030” with a maximum of .010” tolerance for wear. Maximum total bore: 2.6025”. Block may be sleeved and/or decked, but must have one deck angle only--no multi-angle decking.

Stock crankshaft ONLY. Stroke: 2.4370” +/-.010” for wear. Any crank gear may be used.

Stock aftermarket cams allowed, but must have .2330 maximum lift.

Stock head gasket only. NO copper or aluminum head gaskets allowed.

No modification to head allowed. Milling of gasket surface to repair warpage is allowed, but must be done PARALLEL to head bolt bosses, ie. NO angle milling. Minimum valve pocket depth is .280” after carbon removal is done in presence of the tech inspector. NO machining of valve pocket to gain depth.

Stock or stock replacement piston only. NO modifications allowed other than flat milling of piston surface to gain proper deck height. Stock or replacement rings only. Pistons must have three ring grooves with all three rings in place. Stock wrist pins in stock location ONLY. No gapless rings allowed.

NO modifications to block, except block may be decked (see rule #2). Use of helicoils is permitted. Patching of windowed blocks is o.k.

Racing rod is optional, but MUST be stock center-to-center length of 3.875” +/-.005”. Any dipper may be used.

Open exhaust allowed with any diameter or length header pipe SECURELY braced to top of cylinder head. Length of header must NOT extend past rear scrub rail.

Stock or stock replacement ignition points or Magnetron allowed. Any timing key allowed. NO external coils. Must be 5 h.p. coil (black, red or gray face) with Briggs stamp.

Stock carburetor with attached gas tank ONLY. No modifications allowed. No flowed or ported carbs. Maximum venturi diameter: .700”. Smaller venturis may NOT be opened up to .700”. Fun cart carb may be used. Throttle shaft minimum thickness .086 at the front; .050 at the rear. Throttle and choke plate screws are non-tech, however modifying these parts to accept a different type screw is not allowed. Throttle and choke stops are non-tech items.

Stock valves in stock location with stock valve job angles ONLY. No multi-angle valve jobs. Valve lash is optional and not a tech item.

Flywheel must be stock 5 h.p. only. All flywheel fins must be in place. No lightening of flywheel.

Stock or replacement valve springs and retainers ONLY. No shims or double keepers allowed. Upper spring retainers are optional.

Stock lifters of 1.6” only. Lifters that are +.100 are NOT allowed. Billet lifters o.k.

Crankcase breathers are a non-tech item, but no PCV systems allowed.

Any air cleaner may be used, including duct material to feed clean air to carb. NO method of forced induction is allowed.

Pump gas only. No alcohol or fuel additives allowed. Fuel must be readily available pump gas. No airplane fuel. Sunoco, VP or Cam2 is allowed if desired.

Any clutch may be used, except NO belt-driven or torque converter type systems.

If starter is removed, an approved flywheel guard must be in place. ALL engines will have an approved steel scatter shield in place around flywheel area of engine. Minimum measurements of guard: 3”x27”x1/8” steel or 3”x27”x3/16” aluminum.