Anyone lower floats in carb to eliminate bogging?

[ajgraz]

Did a carb rebuild by the book on my 1978 Mercury 70hp 3cyl. New needles and seats, too. Did not change a bogging issue I was having. After reading some threads on motorcycle forums, I tried lowering the floats.

With carb inverted, spec was 11/16" from carb body to bottom of float, I went to 13/16" (which coincidentally put the horizontal seam in the float perfectly parallel with the carb body). I found this to eliminate WOT bogging without (so far as I can tell) inducing any kind of WOT fuel starvation. Also made the motor much more responsive to small changes in idle air/fuel ratio from turning the screws. Motor responds better to choke, too. Also seems to have eliminated fuel dripping out the vent tubes when I tilt up the motor and that light sheen of fuel that always used to show up inside the carb throats.

Seems to me that with the floats set at spec, there was still fuel able to come out the vent tubes. This was apparently making the motor run too rich (at idle anyway) and causing bogging on the transition into power.

Anyone else do this on their outboard (of whatever brand/year)? Lower float bowls to reduce bogging? Any hidden dangers I am not taking into account?

 

[Chris1956]

Re: Anyone lower floats in carb to eliminate bogging?

Don't get me wrong, but you reengineering a successful carb design. Maybe your floats are riding low in the bowl? Maybe your inlet needle is worn out and not sealing properly.

They symptoms of running too lean may be seen in the color of the spark plugs. I recommend you check them out. They should be light brown to nearly black if the motor has the right mixture. Lighter then that may indicate a lean running condition. That can cause a seizure...

 

[ajgraz]

Re: Anyone lower floats in carb to eliminate bogging?

Who knows if these plastic floats are original, and these Sierra rubber-tipped needles and all-brass seats I installed are certainly not original OEM parts. So I agree, these carbs are re-engineered. Fuel is different today than in 1978, so maybe re-engineering is a necessity.

If the floats were "riding low in the bowl," wouldn't that suggest I should raise the floats? Or do I misunderstand? The floats are not cracked or full of liquid, if that's what you mean.

Spark plugs have always been on the fuel-wet side, I will definitely monitor them to see if that situation improves.

From what I've been reading, lowering the float is a pretty common fix for flooding/bogging in both carbed motorcycles and classic cars. So, has anyone else done this on a carbed outboard?