Ported Piston?

[moronic_kaos]

When I was working on a 2-stroke Tomos a few months ago, I noticed something a little different about the piston. The piston on the Tomos has a large port in the side of it on the intake side, whereas these China motors don't have them.

What is the purpose of that port? Could these engines benefit from the same effect, whatever it is? Would it be worth buying an extra piston to experiment with (~$20)? Or is there a technical reason that the port is absent?

(Note: The Tomos worked in conjunction with a reed valve, if that makes a difference)

EDIT: I attached a picture of it (complements of Treatland)

 

[The 26incher]

I'm almost sure the piston port has to be located on the intake side. What it does is allow more gas to be drawn into the engine. A mechanic friend of mine BITD would drill out the pistons on old jet-ski's and they did not have reed boxes. I say go for it and tell us if you gain anything. I don't know how it will effect the balance of the piston?

 

[Mac]

I believe your looking at a piston that is configured with a "Boost" port. You would need the cyl. that goes with it, most likely a set of reed valves... It's as totally different as a 2 stroke design can be, most folks that do the Radio Control(R/C) thing will reco this design. That design makes mucho power, mostly upstairs.

Mac

 

[GearNut]

Without a reed valve, you will get ALOT or reversion through the carburetor.
I simpler terms, alot more air will get pushed backwards through the carburetor before the piston has a chance to close off the intake port.
That will be most noticeable at lower RPM's.
The process:
The air will pass through the carb once, picking up fuel as it should, go into the engine, get blown back out through the carb, picking up more fuel, then going back into the carb again on the next intake cycle, picking up more fuel. You end up with a very rich intake charge as it is triple the proper fuel / air ratio.

 

[moronic_kaos]

Without a reed valve, you will get ALOT or reversion through the carburetor.
I simpler terms, alot more air will get pushed backwards through the carburetor before the piston has a chance to close off the intake port.
That will be most noticeable at lower RPM's.
The process:
The air will pass through the carb once, picking up fuel as it should, go into the engine, get blown back out through the carb, picking up more fuel, then going back into the carb again on the next intake cycle, picking up more fuel. You end up with a very rich intake charge as it is triple the proper fuel / air ratio.

What if there were a way to add a reed to the system? As I understand it, the purpose of the reed valve is to only let air/fuel inside the engine through the intake port, and not out.

So what would happen then? Extra compression in the bottom end of the motor? Or would it just equal itself out and not do anything. Air would be pumped through the piston and through the port, and just close the reed valve & no intake would happen? Or would there be a split second where the reed would be open & vacuum would occur? How would the transfer ports effect the system?

 

[foureasy]

put that tomos alukit on your motor, i made 5 hp to the wheel with a puch alukit. 45mm vs 44mm though

 

[moronic_kaos]

Yea tomos & puch aren't compatible when it comes to the cylinder, which sucks cuz pretty much everything else is. Found that out when I sold a used one and labeled it a "Puch/Tomos K-Start Alukit" and got flamed for it on MopedArmy.

Speaking of tomos.... Got a flat front tire today & threw on my old tomos front mag wheel. Fits perfect and the wider & heavier wheel makes for a WAAYY smoother ride. Too bad it's only a 16" though which puts the pedals about 2 inches above the pavement. If I had a pullstart & centrifical clutch I'd rip that rear wheel right off & replace it with the other Tomos one. Just put some pegs in place of the pedal/crank. It's funny cuz the sprocket fits the chain & the ratio is almost the same when you figure in the wheel size. Plus the brakes kick ass.

 

[foureasy]

i do happen to sell a pretty sweet centrifugal clutch

 

[foureasy]

that holds up to a gila

 

[moronic_kaos]

Hmm... might be interested when I have some money...

Just thought I'd show off my mechanical "aptitude"... haha. The brakes aren't connected yet cuz I don't have a good handle (sold the Tomos ones). The brakes are pretty beefy & would have no problem stopping a bicycle a third the weight of the original moped.

lol... just realized how off-topic this thread got...