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Discussion Starter #1
Hi! I've got a new pocket bike. An X7.

Pretty bad shape. Got it today and started to disassemble straight away.

So what's need to be fixed to get it running.
New piston and piston ring. Ring on top are stuck. And the piston is in really bad shape.
The cylinder though looks okay.

New pull start, I've already ordered it.

I'm almost done to get rid of the electric starter.

There are some pretty rough casting marks in the crankcase.
But I think I will get this one up and running first and then fix it.
So i can feel the difference of the blueprinting, porting etc etc.


159081

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Discussion Starter #3
If someone know what duration that works on those piston ported engines i would be very grateful if sharing those.

I have never ported a piston port engine.
So i have no idea what intake duration needed
 

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Basically to make power with the piston port engine you need to raise the compression.

All you can really do is remove the base gasket or do a head chop.

The intake port duration is controlled by the Piston remove the base gasket then take off the base gasket thickness off the bottom of the intake side piston skirt that sets it about right

if you try to increase the duration too much it will just spit the remaining fuel charge back out the intake

Widen the transfer ports in the usual fashion

Do not try to raise the transfer ports or the exhaust port you need all the compression you can possibly get!!!

You can widen the exhaust Port slightly.

Adding a boost bottle helps reclaim some of the fuel vapors due to the spit back.

The Piston port engine benefits greatly from a very well tuned exhaust.

Piston Port engines also benefit greatly from the rocket key


I didn't do an engine build thread on mine because the thread was more of an entire bike build but here are the pictures from the engine .

Video of it running...

Yes I did paint the bike to match my car.
Lol tacky.
 

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Discussion Starter #5
I've disassemble the cylinder, cylinder looks good. Piston bad.
It's a 43mm bore so can't find a cheap piston for it.
I wet sanded the piston, removed the second piston ring.
Grinded down the piston at exhaust side for more duration. Base gasket delete.
Cleaned the carburetor.
New sparkplug wire.

Now waiting for the pull start to arrive so I can start it up.


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Discussion Starter #8

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It's a bad idea to cut ramps or slots to the piston crown. If you have a normal round style combustion chamber, the piston slots will create pockets in the combustion chamber, lowering compression ratio and creating detonation spots. A cutout that large will probably severely reduce compression ratio.

If the piston just has some scratches, you can easily smooth them out with fine sandpaper. Cylinder bore and piston ring condition are much more important. You can measure the ring gap, anything over 0.5mm is an indication of a worn ring and/or worn bore and will noticeably reduce power.

Tuning a piston port engine... I haven't tuned one myself but I have read a lot of posts about tuning a piston ported Suzuki moped engine on Finnish forums. Usually they recommend the intake duration to be the same as exhaust. Even low intake duration seems to give good power. A good starting point is 180 degrees. If you want really high revs, you need over 190 deg of intake duration, but that will severely impact low rpm operation and it is hard to tune the carburetor, because it will "gurgle" badly at low revs and spit fuel out of the carb...
I suppose this piston ported engine is much better than the reedvalved cag engine in terms of power capability. Basically the piston port can flow more, but the drawback is a narrower power band and harder to tune.
 

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Discussion Starter #10 (Edited)
The intake can't be lowered that much because of the pulse hole.
If using a carburetor with a hose for the pulse it would be possible to lower it more and thread a nipple to the crankcase for the pulse.
Maybe it possible to modify the stock walbro carburetor.

But if going so far that it might benefit to do a reed conversion.
But a well tuned piston port engine's intake sound are great.

For now I will stick with the piston port.

Too bad with the piston.
Can't get a new one cause it's seems to be a rare bore size.
If it breaks i will buy a new cylinder, piston and intake. And maybe a new crank
 

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Discussion Starter #11
Couldn't wait for the pull start to arrive so i decided to use a cordless drill.
But it does not start. Old plug but got a nice purple spark.

But it seemed like there wasn't much fuel on the sparkplug.
So i changed the carburetor for another one.
Also bought a new sparkplug.
Later tonight or tomorrow i will try again.
 

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Couldn't wait for the pull start to arrive so i decided to use a cordless drill.
But it does not start. Old plug but got a nice purple spark.

But it seemed like there wasn't much fuel on the sparkplug.
So i changed the carburetor for another one.
Also bought a new sparkplug.
Later tonight or tomorrow i will try again.
They do not like to be drill started at all...

Make sure you have a spare shank bolt on hand because drill starting tends to snap those.
 

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They don't like to drill start to well don't brake any bolts off
 

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Discussion Starter #15
It starts and runs. Now waiting for the pull start and hopefully I can test it more before it gets too cold.
Then i will start porting it.
But have to test acceleration and top speed first.

Does anybody know a pumper carb with a hose connector for the pulse?
If I can find a pumper carb with hose connector for the pulse i can lower the intake much more and fill the pulse hole in the cylinder with jb weld.
And thread a hose connector to the crankcase.
 

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If you lower that port it's going to spit fuel the piston port engine can only trap so much fuel and then it spits the rest out

Don't listen to trolls telling people to overport their engines

The biggest restriction on the Piston port engine is the transfer ports and the exhaust Port not being wide enough
 

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Discussion Starter #18
I think I'm missing a spacer for the pull start.
Seems like that part is hard to find.
Maybe works with some really thick washers.
Will see when the new pull start arrives.
 

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Discussion Starter #19
Got the pull start today. But they sent me the rectangular pawl with the starter for a circular pawl.
Fortunately I've got the old starter so I'm just going to use that with the pawl.

This is what they sent me.
The black starter is different from the product pictures too.
I sent them an email about sending me the right one.
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