73 115hp Merc. wont accellerate

Joined
Jun 28, 2008
Messages
13
on land with earmuffs the motor performs as expected but with the boat in water, the motor performs differently. At idle it sounds normal. As I put it in gear and give it throttle it just bogs, doesn't bog down, doesn't accelerate enough to plain out either. Doesn't matter if I throttle slow and gradually or punch it WOT. While it was WOT my brother manually choked it and "Shazzam", The boat takes off practically throwing him overboard. Now at the momment he choked it you could hear the carbs sucking hard but I assume thats because the throttle is at WOT. And by choking, it forced fuel into the top 2 carbs, filling the bowls, thus causing the motor to accelerate. I kept it at WOT thinking that if there was some blockage somewhere maybe it would flush out. After about 30 sec. of WOT we lose acceleration so he choked it again and Shazzam again. History repeats itself. We have it figured as a fuel problem so we tried a test to see if we could locate the problem. With the throttle at WOT but the motor just bogging along, my brother shot a burst of starting fluid into the bottom carb. It almost killed the motor but recovered to bogging speed. Shot a burst into the middle carb and same thing happened. Then shot a burst into the top carb and the opposite happens. The motor accelerates till the either burns through. Now my brother and I have different ideas as to why this happens but we are not for sure. If someone could help and explain, and help diagnose the whole problem, it would be much appreciated. Thank you for your helpful suggestions. MIKE
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,100
Re: 73 115hp Merc. wont accellerate

Mike, it sounds like you have two problems. A bad fuel pump and dirty carbs.

First rebuild the fuel pump (s). On a '73 you may have the dual triangle-shaped ones, or the single oblong one. Second, remove all three carbs, clean them out and install new gaskets. Inspect the floats. They tend to disolve after a while. It is likely you need new inlet needles and seats as well. After the carbs are done, perform the link and synch.
 
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