Windowed piston and how to employ

Jack Rutherford /

I put a windowed piston in my qt50 and am trying to get it to play nice. It will start up fine and if I let it idle, it will idle for 10 minutes or so and then eventually die - usually with a - I'll refer to it as a backfire - out the exhaust. If I give it throttle, it will do the same thing much sooner. It also seems to be running very rich. I'm sure I've changed the timing by adding this piston and am wondering if I can make it work adjusting the timing on the engine. Or perhaps make it work through some other method.

I've tried a range of jets including a very small one to no avail. I've searched the army but could only find a post on whether windowed pistons were noisier than non-windowed pistons.

Re: Windowed piston and how to employ

You probably put the piston in upside down, that or your reeds are not sealing

Re: Windowed piston and how to employ

Jack Rutherford /

Well I would be a complete dumbass if I did that but I will not rule it out until I have confirmed. I've had the cylinder off a couple times but did not check for that. Stand by.

Re: Windowed piston and how to employ

Often one has to upjet a ton once using a windowed piston (if) it allows the intake to be open for the entire crank rotation. Sometimes 10 or more jet sizes up

Re: Windowed piston and how to employ

And idling for 10min is stupid.

It tells you nothing about how a bike is running.

Re: Windowed piston and how to employ

Jack Rutherford /

the idling was part of heat cycling the new rings

Re: Windowed piston and how to employ

Oh Jesus help him Jesus

That's 109% wrong.

Idle to warm up then ride it. Ride it hard. That's how ya do it.

Idling 10min won't do shit, except maybe glaze your bore.

Re: Windowed piston and how to employ

Jack Rutherford /

very well

IMG_6254.JPG

Re: Windowed piston and how to employ

Wait, is this new rings in an old cast iron cyl?

If so, did you hone the bore?

Either with a ball hone or sandpaper?

You gotta do that on cast iron bores to break the varnish or the rings won't seat and you'll have shitty compression

Re: Windowed piston and how to employ

Jack Rutherford /

Honed already. Compression fine.

Anyhow, went back to standard piston and it ran like a wet dream. I'll try the windowed piston on a different engine. Try to help out a friend and do something extra and it shits all over ya. (edited)

Re: Windowed piston and how to employ

Edumicate me here- isn't a windowed piston for piston port engines, not a reed valve engine (QT) ? seems like it would totally change suction/intake flow/exhaust flow. ??? Unless you put a matching cylinder for piston port engine. ?? !!

Re: Windowed piston and how to employ

Jack Rutherford /

Don't know if I can educate you but I've seen windowed pistons on reed valve engines.

Re: Windowed piston and how to employ

Overpriced Parts /

> Bob Naske Wrote:

> -------------------------------------------------------

> Edumicate me here- isn't a windowed piston for piston port engines, not

> a reed valve engine (QT) ? seems like it would totally change

> suction/intake flow/exhaust flow. ??? Unless you put a matching cylinder

> for piston port engine. ?? !!

You got it backwards!

Piston port equals no window just a small hole or a few small holes if it has boost ports, Read valve equals window in piston most times,

Now sometimes like the 50cc puch Athena reed kit the piston doesn’t have a window in it just has a few holes cause they send it with wrong piston but it should have a window and a puch Gila has two big holes in piston which you could connect into a window as would be fine,

Stock tomos a35 reed cylinders have two long windows most times

Re: Windowed piston and how to employ

I'm going to put one on my stock MB5, seems like it should have come with one.

Re: Windowed piston and how to employ

I know there’s some scooter kits that the only difference between the “sport” and “race” versions are the pistons. One of the Airsal variants uses the same cylinder, but the “sport” version has no window and I think a different wrist pin height.

Re: Windowed piston and how to employ

Cutting the piston is a must for really good builds. Just cut them yourself with a drill and dremel.

You wanna match the window to the boosts generally, or go bigger.

Re: Windowed piston and how to employ

OG Crazy Wayne /

Race piston with Sunroof

Re: Windowed piston and how to employ

Jack Rutherford /

I think my problem was that my friend's bike had a bad seal that was letting 4 stroke oil into the combustion chamber. I replaced the seal but there was still residual oil in the chamber. The original piston was black everywhere not just the top.

I'll put that piston in another bike and look to reap the whirlwind along with Sheriff Brady.

Re: Windowed piston and how to employ

keen to know how this turns out when you get it going and pics of the window!

Re: Windowed piston and how to employ

Jack Rutherford /

I'll see if I can't make it happen this week. My friend's bike had other issues which may have been causing problems. I'm going to try it on another bike.

Re: Windowed piston and how to employ

Jack Rutherford /

ok windowed piston installed in different qt. Working well. I need to up-jet just a bit more and maybe take a look at how the piston sits at BDC to see if any cylinder changes need to be made.

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