porting stock jug

Im gunna pull off my stock cyclinder tommorow morning wondering if you guys have any tips on porting? Ive never done it before. My plan is to inlarge the intake port to match the square 16 mm intake I have and also smooth out the exahaust port a little any advice greatly appreciated ive searched and read smittys guid to porting just wanted to know if you guys had any maxi specifics for this set up 16mm sha and proma gp

Re: porting stock jug

Widen the exhaust slightly and raise it about 1 mm, not too much. Also cxheck to see if the piston skirt is clearing the intake port all the way, shave piston enough to clear and slightly widen the intake port. When you match the intake make sure to only do it where the intake bolts on the cylinder, not in the cylinder wall where the intake port is.

Re: porting stock jug

what do you mean raise the exahaust port? like so it will change timing?

Re: porting stock jug

yup

Re: porting stock jug

chamfer it well with a small stone in the dremel or (better yet) a small file. you can get some of your low-end back by going to a high compression head or decking your old head. proma gp's are really good with +1.5 mm on each side of the intake, cut 1-2 mm off the piston skirt on the intake side, raise the exhaust .5-.75 mm and widen the exhaust about 1 mm on each side. should put you in the low to mid forties with good acceleration. you can run up to a 16/38-17/40 gear ratio with that and still get full power

Re: porting stock jug

Raising the exhaust means filing away .75-1.0 mm from the front edge of the exhaust port(closest to the head). This lets the exhaust port open a litle earlier and gives it more duration, leting the engine breathe better. Will wind out a little more. Smooth the ports out with emory cloth, and be sure to remove any burrs.

I have done the same thing with my #11 high torque cylinder, shaved head, derestricted stock exhaust,15 bing, 17x41 gearing. On a good day with no wind it will do @44mph.

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