more nubie mikuni carb info help!again

[scabz24]

I got the 18mm carb,thanks for the help guys!another question I had was would a 16mm carb off of a 50cc pit bike work as well,the reason I am asking this is because the guy I got the 18mm from gave me 4 16mm carbs super cheap because he had no use for them they are from a 4 stroke sdg 50cc dirt/pitbke if that helps,just curious because now i have all these carbs and really only need one any info would be appreciated thanks.

[foureasy]

the 16mm would work way better for a stock motor. like i said before, with a little porting and an expansion chamber, the 18mm will rip

[scabz24]

Originally Posted by foureasy

the 16mm would work way better for a stock motor. like i said before, with a little porting and an expansion chamber, the 18mm will rip

thanks again,Ill try not to ask so many stupid questions,just want to build my MB right the first time.,

[ivan H]

I have a vm16-516, which is for a 4 stroke or rotary valved 2 stroke (has bleeder 5 holes in the needle jet) on a 66cc with ports widened a little, top of exhaust port ramped & top of piston ramped in exhaust port area, bottom of intake port ramped also, rocksolid billet head & sbp x chamber. Carb is fine, 25 pilot jet & 72.5 main jet. Cheers

[ivan H]

Sorry, the needle jet has 5 bleeder holes, 3 on one side & 2 on the other,,, not bleeder 5 holes. Cheers

[headtrama]

Hey Ivan I was rejetting my carb today and found out mine has the bleeder holes as well. I am still running a bigger jet then you but I am down to a 90 main now . I am going to have to buy some more jets now .

[ivan H]

Hi Headtrauma, hows it goin. Well I put a bit longer pipe off the header on the sbp x chamber, a 2 & 5/16" length instead of the just under 2" I had to bring the power down in the range so as to be more useable with the gears & after a good 1/2 hour run the plug is the very lightest tan. The c clip is in the middle so I might drop it down a notch. Cheers

[Rocksolidperson]

Hi ivan weve spoken before, the 16mm will work best if you have the mixture perfect, i run a 15.15mm dellorto and it is a beast, the 18mm might be a bit large for this engine, as we are running very similar setups in my sig

[Rocksolidperson]

oh yea and remember we spoke about sbp length how did increasing the length go.?

[ivan H]

Hi Rocksolidperson, hows it going. Yeah, the extra length is going well, I dropped the c clip down a notch on the needle in the carb & the plug is a good healthy color now, about perfect. I agree with u on carb venturi size, too big & u loose velocity so even if theres enough negative pressure to draw the fuel up it doesnt atomise or mix as well. I think that the smallest size venturi that will flow enough air to do the job is always the best one to use. I'm waiting on a rocksolid pull start at the moment, I may order reeds next. Cheers