56ci OMC Carbs - Jetting help?

[Hevi Kevi]

I have a set of carbs here that have L0433699 stamped on them. They are the same size as the SST-60 style carbs but they are off an early 90's 70hp if I remember right and have the adjustable needle valve close to the flange. I'm pretty sure these are jetted much smaller so If I'm running 73 main jets with the SST-60 style carbs, what would get me close for jet size on these ones? Also, what is the base adjustment for the needle valve? I'm guessing it's to fine adjust the idle mixture? I'm hoping someone has experience using these carbs. Thanks in advance,

Kevin

[87vantage]

Kevin, Im working with the same carbs you described, did you have any luck with them? Im using them to convert a 60 to a 70.....

[Fast Fred]

the needle is for low speed adjustment, best to start with what size jet the factory used and go from there.

[87vantage]

Thanks Fred, Do you typically increase the jet size when you bore to .030?

[Fast Fred]

no, factory seems to run a small, small bit fat

[sharpeye Mike]

I know on the 95s the needle valve starting point was 2 3/4 turn, I played with the carbs of a 91 a couple years ago, not sure but I think the starting point was 2 1/4 turn or so.

[oledawg]

:)
I know on the 95s the needle valve starting point was 2 3/4 turn, I played with the carbs of a 91 a couple years ago, not sure but I think the starting point was 2 1/4 turn or so.

If the carbs also have intermediate air bleeds, you will start with .065's for hi-speeds, and 2 1/2-2 3/4 turns on the idle screw. Without the intermediate air bleeds, I would stay with .073's, and go 2-2 1/2 turns on the idle screw. These sizes are factory jets that OMC used. Only use the .073's on an SST-60 type port map. You can stay with .065's on the stock 70 hp.