unrestricted stock carbie

[zingshoen]

who has made some carbie modifications? i m trying to find the optimum setup for a totally unrestricted stock carbie.

history: after changing header pipe and muffler and replacing the airfilter setup with a podfilter stuck onto the air inlet pipe, i ve been using a 140 main jet, the needle in the 3rd groove from below. that worked okay, but i needed the choke on halfway for about 5 ks.

now: i m changing to a podfilter and i ve shortened the intake betwen carbie and cylinder so that i can fit a podfilter angles at 30 degrees.
i ve changed the needle clip to slot 2 from below, but i d like to hear from someone who has experimented with (1) bigger needle jets. the standard is 32;
(2) larger main jets, such as 145 and 150.

also: where can i get bigger needle jets from, such as 36 and 40? what s the zong carbie a copy of? it says "japan" on the side...

[Cal25]

I dont have anything to help concerning jets. Shortening the runner length between the carb and cylinder will increase torque and low end performance. I would assume it would cause a decrease in upper end performance though.

[zingshoen]

well, the shortening came as the simplest solution to some kinda manufacturing or assembly fault, where either the intake or the air box intake pipe were too short, they would just fit, but it wasn t neat and just not leaked.

i don t understand how it would reduce high end performance, but i understand the principle of a sweet spot and that will take some experimenting. at any rate there s not much to shorten, but given the lack of clearance between carbie and monoshock on the ZS GY 10 or 15 mill make a difference.

[homebrewed]

Is this (filter) a bolt-on directly to the carb? I have a 42mm stainless conical filter attached to the carb. Slide needle has been adjusted 2nd from the top (I’m at 8200’/2500m). I have an aftermarket BBR header and exhaust coming. My stock inlet pipe from the air box was also too short which created a substantial gap where they meet. Like Cal stated above I have heard that going to a pod/conical style filter has some negative effects on performance. I believe it has something to do with the vacuum created inside the constant velocity carb. I’m by no means an expert so I’m hoping that someone will chime in with the specifics on this. It’s hard for me to judge after doing the mod since this is my first moto. If this is actually the case I reckon I’ll fix up the stock box and replace w/aftermarket filter.
As for the jets… there should be a model name on it somewhere. My LF-GY has a Sheng Wey PD-2 jap carb. I have seen that the Sheng Wey’s use the Keihin style jets, but use Mikuni sizes. Stock main is 96 or 98 I believe. Check out the jet size converter on the left of the page: http://www.jetsrus.com/main_page.htm
Cheers,
HB

[zingshoen]

thanks for the link, that s a good reference for me!