Hi Im replacing my 12mm phbn hs carb for a 17.5mm phbn. When installing the new carb do i use the set up that came with the new carb as a start off point or would i aim more for the old set up? Basically... 12mm carb...air/mixture screw 1 3/4 turns out. Mj 72 New carb.... 17.5mm....air/mixture screw 3.5 turns out Mj 90 Its for a neos 2 stroke. Standard airbox. New but standard reed valve. Technigas silent pro exhaust derestricted. Im just looking for a starting point not someone to give me an answer for correct jet size as everyone as to learn sometime. Thanks
Can someone help me in the right direction please....im not looking for the answer as we all tend to join forums for a quick fix i want to work it out for myself.....apart from where to start. The 17.5 carb came with a mj90...i know thats going to be too big for my set up. Standard 1998 50cc neos, apart from derestricted technigas silent pro exhaust which i know is not a top of the range one. Problem i have is where to start from...i dont want to start at 90 and then find im changing all the way down to day a 68. The other area where im confused is the air/mixture screw...is it 2 turns out? 1 1/2 and so on. It came wound out by 3.5 turns which i have read is standard. Any help is greatly recieved.
It's going to be a case of re-jetting the carb to find the best jet I'm afraid. The first thing to do I suppose is whack it on and see how it goes, but I suspect you will be going down in sizes somewhat. As with any new mod, especially carbs and pipes, you have to find the right "mix". Buy a pack of jets ranging from 75 to 100, start at the biggest and work down from there.
Can I ask what is the benefit of using a larger carb? Surely the cylinder can only take in a certain volume of fuel air and so how does increasing this help?
