Mercruiser 140 Mercarb bog

[rjs65]

My buddie and my 1986 Bomber Fish and Ski with a Mercruiser 140 I/O bogs and will die upon takeoff unless the throttle is slowly eased in or worked back and forth. Once the rpm's are up to about 2K, it will accelerate normally and runs great.

We've rebuilt the carb twice and adjusted the float and throttle (accelerator) pump to spec. First question: The rebuild kit contains two steel balls, one larger than the other. Which one goes under the pump discharge spring which is held in place by the pump spring guide?

Second question: the idle adjusting needle seems to do nothing when turned. Why? Any and all suggestions are appreciated.

 

[JustJason]

Re: Mercruiser 140 Mercarb bog

1. Whichever checkball you took out you put back in. You can measure it with a set of verneers. Hope you didn't lose the old one. On these carbs, i don't bother replace the ball unless the old one is pitted up or rusty.

2. There are 2 idle adjusting needles, and we need to be on the same page as to which one your refering to. There is the idle speed screw, which sits on the side of the carb on it's linkage. Then there is the idle mixture screw(s), which sit in the throttle plate (lower) section of the carb.

Before you touch fuel you need to check your base timing and check for correct advance. You really oughta do a compression test to. Just for ships and giggle, and to rule every other possibility out.

If your compression and ignition system check out, it sounds like your accelerator pump circuit on the carb isn't pumping correctly. Pull the flame arrestor off, disconnect the throttle cable, hold the choke open by hand. Start pumping the throttle and see if you see 2 solid streams of fuel shoot down the carb's throat. Anything less than a full hard stream means something is wrong. And do this with the boat off... you don't need it running.