Who knows 2-strokes?

I’m slowly realizing I know jack shit about 2-stroke motors.

I took my top end off.

From what I can tell… Some dip shit before me put in a reed-valve piston into a piston-port engine.

Let me back up a step if you know jack like me.

Apparently in these old shitty jap 2-strokes, there are piston-port heads and reed-valve heads. Reed-valve is the newer style of the two.

Basically it means what style of air / fuel intake is it. Piston-port uses the piston as the intake valve and the exhaust valve. Reed-valve uses flaps and piston as the intake valve and the piston as the exhaust valve. I’m sure my explanation is ultra generalized but from a beginner understanding it’s probably fine.

Anyway, my engine is the older piston-port but when I took the head off the piston in it was a reed-valve piston since it has the holes on the intake side.

The holes on the intake side of the piston lets the intake flow draw more air in which is something reed-valve heads want / need.

No idea why someone put a reed-valve piston in a port-piston head. The holes would draw too much air from my understanding. I’m assuming it was a dip shit and this is one of the reasons the bike ran like total garbage. Anyway, I’m putting in a wiseco piston and doing the crank seals. Plus I’m going to try shaving down the bottom of the intake skirt a tiny bit as the dude in one of the bottom images suggests since I have a pod filter and jetted carb.

Overall I’m cleaning this thing up a bit because it’s a piece of junk right now.

Anyone know 2-strokes and have input / suggestions for me?

Oh… and this thing is a joke to work on. Took like 5 mins to rip off the little shit it had on it. And another 5 mins to take the top end of the engine off.

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Piston on the right is the wiseco piston and the correct type of piston for a piston-port head.

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5 responses to “Who knows 2-strokes?”

  1. Carson says:

    If you’re going to raise the intake side of the piston, I would suggest raising the exhaust port the same amount to allow for an even flow. If you’re gonna let more fuel and air in sooner then you also should allow for the sooner release of exhaust gases as well.

    Side to side you can open up the transfers, intake and exhaust ports pretty much to your hearts desire, but once you start going top to bottom you start to play with the intake and exhaust timing and that can get confusing real quick.

    if you start playing with porting, make sure to leave the intake rough, as that helps to mix the air and fuel, but polish the exhaust port to allow a smooth exit.

    I’d also suggest looking for an expansion chamber if you really want to get a kick in your ass on that thing. Thats gonna be a fun little bike to rip around on.

  2. Steve says:

    I love how simple 2 strokes are and how easy they are to modify/fuck up. Going to try to get more power out of my ’79 250 this winter. Started reading this:

    http://www.amrca.com/tech/tuners.pdf

  3. Ed says:

    @carson
    I might not fuck with the piston at all.
    It has a pod filter so I opened up my jets a bit… But other than that I might not do anything else.

  4. Carson says:

    @Ed

    theres really no need to mess with the piston. Unless you get into some heavy porting then you’re not really going to notice a big difference.

    Those little bikes haul pretty well without any modifications. But if you want a little more kick out of it, my best suggestion would be a pipe and to re-gear it.

    The only thing I did to my little Suzuki GT185 is swap out to pod filters, up jet, and modify some old RD250 pipes to work on the bike. It brought the power band on the pipe up from the bottom end to the mid-range and the bike rips now.

  5. Brett says:

    If you have a reed injection, look into getting some Boyesen power reeds. Did a uni filter, re-jet, power reeds, and mx expansion chamber. Went from 28 rhp to 37. Also running 16/39 gearing, from 14/50. A little more carb tweeking, and I should be real close to hitting the ton. Not bad for a Yammy DT3 250.

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