Re: Irregular idling Weber
Posted: Fri Oct 02, 2015 9:31 am
I`m still at square one with a couple of things I don`t understand. You say the stock pistons were 9:1 compression ratio. I`m not aware there were different types in the Paso engines. Never read anything else than 10:1. The Supersport came with 9:1 CR.
Is yours still the original Pantah/Paso engine?
You write you have this filter and Laser exhaust pipes but are using a main jet that`s smaller than the original and an air corrector jet which is larger than the original, hence leaner. I`m no carb expert but to me that doesn`t sound right.
Figuring out the compression ration doesn`t need any equipment. With bore and stroke you calculate the cylinder volume. What can be more tricky is to figure out the volume of the combustion chamber. This is the inner volume of the cylinder head. This volume is impacted by the piston position at TDC (deck hight). If it`s lower than the cylinder top this volume ads to the cylinder head volume. If the piston is higher it decreases the volume. It gets more complicated if the piston has a dome and the piston is lower than the cylinder top while the highest part of it is above.
The area between the top land (the part between the upper piston ring and the piston crown) and the cylinder wall also is a volume that`s added to the combustion chamber volume.
The volume of the cylinder head is determined by turning it upside down and filling it up with fluid and a syringe.
With these numbers you can calculate the current compression ratio.
If you know the compression ratio you`re aiming for you can calculate the required combustion chamber volume.
https://app.box.com/s/69k6z5jjv7s8ze6pnjn9mqgfpemgmel7
This a 2 stroke book but the cylinder head info is worth reading
https://app.box.com/s/oigjlb9f7y2gnhrmm50ainhrv7dtd3mj
If you really had high compression pistons you would have to install colder spark plugs. (NGK 9 instead of 8 ) but that`s not necessary if you`re using original Paso pistons.
Is yours still the original Pantah/Paso engine?
You write you have this filter and Laser exhaust pipes but are using a main jet that`s smaller than the original and an air corrector jet which is larger than the original, hence leaner. I`m no carb expert but to me that doesn`t sound right.
Figuring out the compression ration doesn`t need any equipment. With bore and stroke you calculate the cylinder volume. What can be more tricky is to figure out the volume of the combustion chamber. This is the inner volume of the cylinder head. This volume is impacted by the piston position at TDC (deck hight). If it`s lower than the cylinder top this volume ads to the cylinder head volume. If the piston is higher it decreases the volume. It gets more complicated if the piston has a dome and the piston is lower than the cylinder top while the highest part of it is above.
The area between the top land (the part between the upper piston ring and the piston crown) and the cylinder wall also is a volume that`s added to the combustion chamber volume.
The volume of the cylinder head is determined by turning it upside down and filling it up with fluid and a syringe.
With these numbers you can calculate the current compression ratio.
If you know the compression ratio you`re aiming for you can calculate the required combustion chamber volume.
https://app.box.com/s/69k6z5jjv7s8ze6pnjn9mqgfpemgmel7
This a 2 stroke book but the cylinder head info is worth reading
https://app.box.com/s/oigjlb9f7y2gnhrmm50ainhrv7dtd3mj
If you really had high compression pistons you would have to install colder spark plugs. (NGK 9 instead of 8 ) but that`s not necessary if you`re using original Paso pistons.