The Marine Doctor

[ChuckGleaves]

Doc,<br />I just rebuilt two carbs on my 1979 80 hp merc. Can you give me some tips on tuning it in? Is the only adjustment the needle valve? Does srewing it in reduce fuel flow to the floats? Thanks for the help.

 

[The Marine Doctor]

Re: The Marine Doctor

The low speed needles control the amount of fuel needed for idle. Turning clockwise lessens or leans the air/fuel mixture. While turn it counterclockwise increases or enrichens the amount of fuel to the engine.<br /><br />Start with 1 1/2 turns. Then adjust accordingly. <br /><br />Start engine allow to warm up. Shift into gear. Starting with the top carb slowly turn the low speed needle clockwise. Listen for the engine to start to stumble. Once it starts to stumble, turn the screw counterclockwise 1/8 of a turn. Let it idle for about 30 seconds to see if it will run smoothly. If not..repeat process and increase the back out to 1/4 of a turn.<br /><br />Repeat for both carbs. <br /><br />High speed in Not adjustable.<br /><br />Keep in mind....that 1 1/2 is the starting reference point...generally the engine will perform fine with this setting.<br /><br />TMD

 

[greasemonkeyozi]

Re: The Marine Doctor

I had recently rebuilt my carbs on a 75 70hp merc motor that may be similar to yours. This retired master mech gave me some advice on these adjusting screws on these type motors. He said, Turn clockwise until snug all the way until screw meets needle, not too snug or i would taper the needle. Turn counter clockwise 2 rotations. <br /> So far my motor runs like a champ, not too lean, not too rick, but right on the spot.