WHAT MOTOR DO I HAVE and IS 38mm or 40mm stroke better ?


Apr 30, 2016
I ordered a SILVER FLYING HORSE (i think its the same as the SILVER SLANT but with CNC motor mount)) KIT from GASBIKE,,I was surprized that the engine came with a real clean looking cylinder (not to much cleaning to be done with dremel,, little ridge in square transfer ports)).. it has the ZAE 80 connect rod, the smaller piston with wristpin in center and .60 domed piston,, slant head, my cylinder has a thicker base then other cylinders I see,,, which is good cause it acts like running two base gaskets which raises exhaust port an transfers,,, I can still see about 2mm of the piston skirt thru intake port at TDC,,, **(should i grind the piston skirt on intake side and how much if i am starting with a 2mm overlap))**???? motor has wider wristpin bearing,,, the magneto is dated with the year 10, 4 holes not the old six and three wiries black ,,blue,,white,,.. is this a GT5 engine,, has good power ,,, but with 44 tooth sprocket I max out at 34.7mph confirmed with speedo, gps, and friends car,,,but my cheap $10 hour// tachometer says like 1400 rpms at idle 2500-3000 at 25 mph and a top 4200 rpms at flat out wide open flat road 34.7 mph....wont rev any higher... what is the difference between pistons and 38mm and 40mm stroke engines,,,which is better...and what is my top RPMs supposed to be with BANNANA PIPE, RSE head and all i have done is port match and bottom case match and gasket match and raised exhaust port up 1.5mm and widened the exhaust and intake ports 1.5mm on each side... thats it....please help answer all these questions,,, sorry its alot


Well-Known Member
Nov 28, 2012
sf bay area
Sounds like your tach is counting half for a 2cyl or something. You need to go into the settings and set it to a single cylinder. as for the other questions I can't help you there. Wide open you should be reading closer to 10k not 5k.

Can I make a suggestion? Split your post up into paragraphs to make it easier to read (like this) you will have a higher chance of getting all your q's answered.


Well-Known Member
May 1, 2011
Newnan,Georgia U.S.A.
The stroke can be measured with the head on, remove the sparkplug and measure the distance from the piston to the top of the head with the piston at tdc, then move the piston to bottom dead center and measure there. Subtract the first measurement from the 2nd and you have the stroke. A unsharpened pencil will work as the depth tool.