Nikki Carbs
Thread Starter
Senior Member
Joined: Jul 2004
Posts: 270
What modifications would i have to do to the carb on this engine setup. 12a, fairly large streetport, the runners on housings and intake have been ported/polished, its running carbon seals, lightened flywheel, aftermarket header, no cat, and flowy exhuast, Thanks, Mike
Junior Member
Joined: Aug 2004
Posts: 17
From: Auckland City, New Zealand.
I've had a couple of nikki's modified by carbie people, as far as I can tell, from pulling them down afterward, they machine out both the primary and secondary venturi, change the needle valve and machine up a 3mm valve, and the floats have been modified aswell.
Member
Joined: Aug 2002
Posts: 70
From: Orlando, Fl.
Ok, now I know why you PM'd me. You can fix this by simply roughing up the runners with 80 grit or so sandpaper. Modding the Nikki carb will get the airflow you need, especially for a SP. Even a stock 12A can benefit from a bigger carb and better flowing intake manifold and airbox. Now once you hog out your Nikki's venturis, youll have to completely re-calibrate the jets and bleeds so the fuel curve is right. Believe me thats alot of time and work mang. Go over to www.pbandjracing.com or www.sterlingmetalworks.com and read about our carbys.
And for the record heres the reply to your PM. It might shed some light on the subject for others.
On a wet flow (air and fuel flowing thru it) intake manifold you want a rough surface (like sandpaper). This will keep some turbulence going on the runner walls, which prevents a boundary layer from forming, which will reduce fuel seperation so you get better atomization and a more homogeneous mixture. Fuel being heavier than the air will want to stick to the walls of the runners, especially in the bends (it wants to keep going straight cause it has more mass than the air and cant turn as easily), this will cause puddling of fuel and raw liquid gasoline entering the engine, which wont burn well cause its not atomized and mixed with the air. Thats the situation your trying to avoid. Thats the short answer. Volumes have been written on the subject and theres some great reading on the net if you want to get deep into airflow dynamics in an internal combustion engine. HTH
And for the record heres the reply to your PM. It might shed some light on the subject for others.
On a wet flow (air and fuel flowing thru it) intake manifold you want a rough surface (like sandpaper). This will keep some turbulence going on the runner walls, which prevents a boundary layer from forming, which will reduce fuel seperation so you get better atomization and a more homogeneous mixture. Fuel being heavier than the air will want to stick to the walls of the runners, especially in the bends (it wants to keep going straight cause it has more mass than the air and cant turn as easily), this will cause puddling of fuel and raw liquid gasoline entering the engine, which wont burn well cause its not atomized and mixed with the air. Thats the situation your trying to avoid. Thats the short answer. Volumes have been written on the subject and theres some great reading on the net if you want to get deep into airflow dynamics in an internal combustion engine. HTH
Member
Joined: Aug 2002
Posts: 70
From: Orlando, Fl.
Im afraid to ask, but what are the venturi sizes now? Youll have to tune it from scratch now. A dyno and a handful of jets would be the easiest way. You could also setup an A/F meter and tune it driving on the street.
Thread Starter
Senior Member
Joined: Jul 2004
Posts: 270
i will go measure, i got my dad to help me on the porting of the venturis because he has done that stuff many times before i have the a/f guages and sensors and stuff made by autometer lol but i doubt i could use that, it think we will just do some steet tuning until it is somewhere, where we like it and then do a couple dyno pulls, because up here dyno times is super pricey, thanks, mike