Porting

yeah these stock motors are made so out of tune on so many levels its almost impressive but its more sad than impressive

but at the same time that's what makes this hobby/sport so enticing nd exciting just trying to make poor craftsmanship what its sposed to be

ive run several stock motors and they seem to perform just fine but still they could be way better

supprisingly once u get a good drivetrain configured the little ht's r quite reliable at least for in town usage.

the biggest problems ive had where with the chain tensioner intill i just made my own with a skate boar wheel and flat bar of steel

WildAlaskan said:

im not sure if this is better but i think instead of skirt trimming ur piston, wouldnt it b better to raise the jug to clear the skirt and then shave the top of the jug down to u[p compression.

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Sorry, I'm not exactly sure what you mean.

I'm only young so I'm somewhat learning as I go. Bare with me here.

what i mean by jug is the cylinder. it seems to me that the cylinders of most if not all chinas r too low for the bottom of the piston(pison skirt) to clear the fuel/air intake(meaning when piston is top dead center the bottom of piston (piston skirt) doesnt clear the intake port) restricting airflow reducing go juice flow

WildAlaskan said:

what i mean by jug is the cylinder. it seems to me that the cylinders of most if not all chinas r too low for the bottom of the piston(pison skirt) to clear the fuel/air intake(meaning when piston is top dead center the bottom of piston (piston skirt) doesnt clear the intake port) restricting airflow reducing go juice flow

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Oh I understand what you are saying. What I did with mine was cut the area that is in the way of the intake port (used a sharpie to mark the area covering the intake port while piston was at top dead center). The exhaust port seemed fine on my engine however.

The only thing is you can't notch the piston too much since it is opening the intake quicker. If you go too far with the notch in the piston your engine won't run too well.

I think we are saying the same thing, just different ways. Thanks for clearing that up though.

To port or not to port. That is the question?
I say port that!!! But I'm also on like my fifth motor. But this motor is frickin' sick!!
I matched the transfer ports. Matched the gaskets.
Ported the exhaust and matched up the gasket.
On the inside of the cylinder I cleaned up all the castings. Notched the top of the exhaust port. So it's not a sharp edge.
With that said I say port.

WildAlaskan said:

what i mean by jug is the cylinder. it seems to me that the cylinders of most if not all chinas r too low for the bottom of the piston(pison skirt) to clear the fuel/air intake(meaning when piston is top dead center the bottom of piston (piston skirt) doesnt clear the intake port) restricting airflow reducing go juice flow

Click to expand...

I just use thicker cylinder base gasket material since I never use MFR gaskets and make my own.

Interesting read and wish I found this before starting in on my GT-5 today. This is my first MB build but I go pretty far back as far as porting 2 strokes and after tearing down my engine today I decided rather not to do much porting, but more of a port matching thing.

This is what I found on my intake and what I did.











To be continued.

Like most of yall, I didn't go overboard and know that a finely polished intake is reduces atomization, so I left it a little rough.

In 1972 Yamaha Inc. gave me the low down on timing the piston's lower skirt to the transfer ports to allow more fuel to enter the combustion chamber, but that was a rotary valve 71 Mini Enduro vs: what I assume is a true "Piston Port Timing" engine. I soon realized that timing to the transfer ports was not an option so I marked my piston skirt for trimming at TDC. Hope I'm on the right track.

Tomorrow I start on the exhaust and transfer ports.