Category talk:Performance Tuning

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The terribleness of this article makes my brain hurt.

then fix it! Duh.

What am I, made of effort?

Batavus M48 cylinder port timing / map mods

   * Attachment: 1223875321_m48_bat_156_deg_port_mods004.jpg

Thees M48 Batavus cylinder port,s power band mods Run WOT all day. A Exhaust port duration 155 Deg gives 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.

Batavus M48 cylinder port timing / map mods

Port tuning for 4,500 to7,000+ RPM’s 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 9.4 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. NOTE torque head in 4 steps - 1st torque to 2ft lb - 2nd torque to 4ft lb - 3rd torque to 6ft lb - 4th torque to 8ft lb and re torque to 8ft lb.

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. (not top of cylinder) 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. (not top of cylinder)

Intake / transfer ports Ports open 121.5 deg ATDC. Ports open 31 mm / .1.220” ATDC. (not top of cylinder) 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. (not top of cylinder) Taper and deberr transfer ports. Save the last .5mm=.020”of porting for Hand touch up and Polishing.

Power band starts at 22MPH=3,800RPM's Kicks in at 25 MPH=4,500RPM's peaks at 37+ MPH=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,


Crazy Wayne out