i am putting a 48 IDA on my large SP 12A and i was wondering if someone could recommend a good starting point for the jetting. main jets, air jets, emulsion tubes, idle jets, needle seat, and venturi's.......

thanks in advance

 

Mains-----170
Air---------150
ET---------F-11
IJ----------62
NS-------- 250 or larger
V---------- 37mm

 

isn't 170 a little small for the mains?? the last guy i talked to was running up around 200 mains with a similar engine to what i will be using.

 

The size of the mains is dependant on the size of the venturi.
I've seen over 200 mains but with a much larger venturi. I've seen 280 mains on some setups that were also too lean. If you want start with a 200 main then. You never go wrong to start rich and then lean it out.
It's just a starting point. No set up is the same. You'll have to tune it to get it right. You just can't guess at tuning although I've done it a couple of times!

 

Crispeed is right - jetting and venturi size are tied together. You better make sure what size venturies you have. I am using the same jet & venturi numbers Crispeed said in my street port 12A with 48 IDA .

It really helps to use an air/fuel ratio meter to get your jetting right; it will save you a lot of time if you use the A/F meter.

 

For street use, 37 is too small.

 

the car will only be driven on the street during break-in and the occasional mid-night crazy runs. other than that the car is only driven on road coarses and autox. thanks for the starting points guys, hopefully it will save me tons of time trying to get it close.

 

The old rule of thumb is venturi size X 4 for mains then add about 50 for airs. The rotary seems to blow the old rule (piston) out the window and wants a lot more fuel, hence bigger mains AND smaller airs. We have a 13B with 42mm chokes running 220 mains and I think 190 airs. E-tubes are all strange on the numbers some flow close to the same but have way differet numbers. F11's seem to work for us also.

 

jgrewe: are you driving your 42mm chokes on a daily driver street car? I don't think they would be streetable even for a 1000 miles of break in use.