Engine Trouble 2 Stroke has no low end

[MinimumVK]

Hello 2 smoke experts! I have a scooter that i got for pennies on the dollar and i fixed 90% of it (mostly wiring and some engine stuff). So the issue im having is that below 5000rpm the thing is gutless. It can barely take off on a flat road and its running way way too rich on the pilot circuit. Now heres the catch... 3 carburetors, 2 of them are from working scooters and one is an OEM Dellorto PHVA 12mm made for scooters with manual choke that i bought so i could rejet it and experiment. None of them work including the Dellorto. No amount of jetting, adjusting or anything gets it to even idle above 700rpm. I checked everything on the scoot except the cylinder and piston (PO did a rebuilt) so its not any of the seals, electrics.... If i can get it to rev up with lets say a 90 main jet it 4 strokes but only close to the red line. Idle isnt affected by anything.
The previous owner did bore the cylinder and he said that he didnt port it (to belive or not belive?). I will take it apart and check the cylinder but i want your opinion on the matter. All i can find on google is that bad porting does affect the engine but not how.
So could bad porting in my case have an effect on low-mid range power? After it passes 5000rpm it power wheelies. Piston is new and compression is 150psi.
EDIT: Almost every scooter forum is dead and i know you guys know alot about 2 strokes so thats the reason im writing this here.

 

[ImpulseRocket]

Sounds to me like there is definitely something off with the port timing or one of the ports if everything else is good.

I rarely trust anybody else's rebuilds unless I know the person AND know they do good work with quality parts. That cylinder he used may have been a crappy cheap one.

 

[Mike Cyanide]

Hello 2 smoke experts! I have a scooter that i got for pennies on the dollar and i fixed 90% of it (mostly wiring and some engine stuff). So the issue im having is that below 5000rpm the thing is gutless. It can barely take off on a flat road and its running way way too rich on the pilot circuit. Now heres the catch... 3 carburetors, 2 of them are from working scooters and one is an OEM Dellorto PHVA 12mm made for scooters with manual choke that i bought so i could rejet it and experiment. None of them work including the Dellorto. No amount of jetting, adjusting or anything gets it to even idle above 700rpm. I checked everything on the scoot except the cylinder and piston (PO did a rebuilt) so its not any of the seals, electrics.... If i can get it to rev up with lets say a 90 main jet it 4 strokes but only close to the red line. Idle isnt affected by anything.
The previous owner did bore the cylinder and he said that he didnt port it (to belive or not belive?). I will take it apart and check the cylinder but i want your opinion on the matter. All i can find on google is that bad porting does affect the engine but not how.
So could bad porting in my case have an effect on low-mid range power? After it passes 5000rpm it power wheelies. Piston is new and compression is 150psi.
EDIT: Almost every scooter forum is dead and i know you guys know alot about 2 strokes so thats the reason im writing this here.

My guy impulse rocket know his stuff. He sounds dead on. I'd look at the shapes of the ports and transfers first. Steep tranfers,more circular exhaust port say high rpm power but dead off the line torque. Sounds like a neutral drop motor lol has to be wide open to run at all... like a full race motor.

 

[Mike Cyanide]

Hello 2 smoke experts! I have a scooter that i got for pennies on the dollar and i fixed 90% of it (mostly wiring and some engine stuff). So the issue im having is that below 5000rpm the thing is gutless. It can barely take off on a flat road and its running way way too rich on the pilot circuit. Now heres the catch... 3 carburetors, 2 of them are from working scooters and one is an OEM Dellorto PHVA 12mm made for scooters with manual choke that i bought so i could rejet it and experiment. None of them work including the Dellorto. No amount of jetting, adjusting or anything gets it to even idle above 700rpm. I checked everything on the scoot except the cylinder and piston (PO did a rebuilt) so its not any of the seals, electrics.... If i can get it to rev up with lets say a 90 main jet it 4 strokes but only close to the red line. Idle isnt affected by anything.
The previous owner did bore the cylinder and he said that he didnt port it (to belive or not belive?). I will take it apart and check the cylinder but i want your opinion on the matter. All i can find on google is that bad porting does affect the engine but not how.
So could bad porting in my case have an effect on low-mid range power? After it passes 5000rpm it power wheelies. Piston is new and compression is 150psi.
EDIT: Almost every scooter forum is dead and i know you guys know alot about 2 strokes so thats the reason im writing this here.

Literally just google 2 stroke port map and Marty's garage will pop up first. La hover bikes mention him. Good info what your saying track to that alot

 

[Mike Cyanide]

Two Stroke Port Duration

Port Timing Basics Air/gasoline enters the engine from the carburetor at a ratio close to 15:1. It enters via the intake port (as the piston rises) into the crankcase and then is transferred to the combustion area via the transfer ports (as the piston descends and the piston top uncovers the...

martysgarage.info

 

[Mike Cyanide]

There ya go

 

[MinimumVK]

Sounds to me like there is definitely something off with the port timing or one of the ports if everything else is good.

I rarely trust anybody else's rebuilds unless I know the person AND know they do good work with quality parts. That cylinder he used may have been a crappy cheap one.

So this is what i found inside the engine...
1st thing i noticed is that the piston doesnt have a window in it so they installed a piston made for another cylinder type.
2nd thing is that the transfer ports are at an angle and when they honed it the transfers moved a little bit.
Im not an expert on the tuning aspect on these things but after doing a bit of research people have said that not having a window effects port timing and can mess up the powerband. It was weird that they only changed the piston as to my knowladge the cylinder and piston are made to work together in terms of port timing.
Time to order a 70 kit i guess

 

[Gordy]

Try windowing the piston before you order a new cylinder kit

 

[MinimumVK]

Try windowing the piston before you order a new cylinder kit

I did think of that but i dont have a dremel and a template for the window. Might aswell change it if i have it apart. A brand name kit is about 130 euros with piston, cylinder, head and gaskets.

 

[Chainlube]

So this is what i found inside the engine...
1st thing i noticed is that the piston doesnt have a window in it so they installed a piston made for another cylinder type.
2nd thing is that the transfer ports are at an angle and when they honed it the transfers moved a little bit.
Im not an expert on the tuning aspect on these things but after doing a bit of research people have said that not having a window effects port timing and can mess up the powerband. It was weird that they only changed the piston as to my knowladge the cylinder and piston are made to work together in terms of port timing.
Time to order a 70 kit i guess

Are you still talking about the scooter? It won't have a windowed piston. Do you have a picture of your engine?