Re: Merc Carb Accelerator Bog
raise your float level, and make sure you have a good amount of float drop! <br /><br />I've been going through this problem with my 2002 Bayliner 3.0L with 2bbl mercarb. Would always bog, no matter how slow you push the throttle down- this means it's not the accelerator pump! If you have the same carb year, then this should apply directly.<br /><br />I finally cured the problem with 1.65mm jets versus the stock 1.55mm; pulled carb apart a 2nd time completely and cleaned everything really good, and purchased a $40 carb tuning book to understand what I was doing.<br /><br />The bog at 2000 rpms, for me anyway, is in the compensation circuit of the carb, before the main circuit comes online. Right above the throttle plates are two small vertical slits. This, and the passages within the carb body, is the circuit the carb operates at that speed where the bog occurs. Make sure it is completely clean, and has no dirt or varnish impeeding fuel flow.<br /><br />Per the merc #26 manual for my carb, it lists 14mm float height with spring loaded needle and 27mm float drop. Looking at mine, there's no reason the float can't drop to the bottom of the bowl. So I set it that way. For float height, I think the merc manual specifies an incorrect measuring point on the float for measuring. I'll have to borrow it again and reread it. But I used the other dimple on the float, which would make it seem to float really high. But now I do not have the bog anymore, nor the occassional pop at high rpms (from running lean). Motor runs great.<br /><br />My understanding is, from my carb book, the fuel level in the bowl should be to where it's just under the height where it enters the carb throat. Any higher and it would freeflow into the throat and flood the motor. When float level is too low, vacuum has a hard time pulling enough fuel up through the carb circuit and out the boosters, and runs lean. And it will also cause the carb not to transition between circuits- the compensation circuit to the main circuit (2000-3000 rpms). It causes a hole in the air/fuel mixture, which is "the bog", then the get up and go". That's your carb transitioning between it's compensation circuit into the main circuit.<br /><br />For me, I don't know how much the 1.65mm jets had an effect. But I had them in there and still had the bog, which was worse even and I was also getting an occasional backfire at high rpms. So it was the good cleaning I did, and raising float level which fixed everything. I have my accel. pump lever in the middle hole; I have no problems jamming the throttle open and the boat getting out of the hole. <br /><br />The book I got was Carburetor Performance: How to Tune & Modify (Motorbooks Powertech Series). I highly recommend it, if anything just for a good read.
