File:M48 bat 156 Deg port Mod's004.JPG
Batavus M48 Port tuning for 4,500 to7,000+ RPM’s 155 Deg duration port mod's give strong better than stock low end power with one cylinder base gasket with a duration 155 Deg or less over 156 you start lousing low end power. HP approx 4.2+. With stock red block. S-25 Encarwi Carb With mod’s 15+mm in 13mm venture 12.8mm out. Set float 12.5mm pin tip to top of float Jet #64. Stock intake Mod’s. 13mm in 12.3 mm out. Timeing .085”/ 26 Deg BTDC Stater at mid point +. Gap B8HS .021”.New points gap.0155”. Stock 26mm EX with power band Mod,s
Cut top of cylinder.024”.(Note Dome of piston shod rise 1mm=.039” above cylinder at TDC ). This shod give 16.6mm=.655”=21/32,s(NO LESS) top of piston dome to fin side/top of head where spark plug gasket sits on top of head at hole. ( You can use a tire tired depth Test it gauge cut sides to fit & Grate for timing to) Mill head To set gap Mill .?mm.0??” off head (Tip of spark plug must be 1mm=.039” or more away from top of piston dome at TDC) Approx 9.4or9.5 to 1 compression If you go higher it can over heat eng/stock piston/ping make you use less spark timing=Less power at 6,000+RPM’s
CK with 1 base gasket Head torqued to 8 ft lb (not 11 ft lb maul TYPO ? ) Don’t brake it.
Displacement 47.75 cc. Bore 40 mm / 1.575”. Stroke 38 mm / 1.496”. Exhaust port duration 155 Deg=port height 13mm ovule shape Like Stew’s Head or a football width 24.5mm. Exhaust port opens 102.5 deg ATDC. Exhaust port opens 25 mm / .984” ATDC. Port height 13 mm / .512”. Port width 24.5 mm / .964” = 60% of Bore. Polish and (taper exhaust port opening on piston side) don’t brake a ring. The exhaust port should open .984”=25mm=102.5 Deg ATDC.
Intake / transfer ports Ports open 121.5 deg ATDC. Ports open 31 mm / .1.220” ATDC. Intake / transfer ports duration 117 deg. Ports height….. 7 mm / .275”. Shape transfer ports like a long long tear drop pointing away from exhaust port. Transfer ports opening’s must not taper or point on exhaust port side of transfer port opening. Ports width….... 17 mm / .669”. Make the transfer ports point 25 deg’s away from exhaust port. Transfer ports need to open at 1.220” inches=31mm=121.5 deg ATDC. Taper and deberr transfer ports. Save the last .5mm=.020”of porting for Hand touch up and Polishing.
Power band starts at 22MPH Kicks hard 25 MPH to 37+ MPH peaks at 6,700 RPM,s Fads at 38 MPH and Fore stroks at 7,000 RPM’s = 39+ MPH with those Dam stock carb & reed’s
I hope this engineering witchcraft help,s you get your Bat going faster, PS i will post more pics.
Crazy Wayne out
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