1986 Mercury 175 hp. part throttle Surge

[Joe Sergi]

I have a part throttle surge at 3000 to 5000 rpm The engine was rebuilt 100 hrs ago. I just rebuilt the carbs they are wh-46 just rebuilt the fuel pump replaced all lines. runs perfect at idle up to 3000 runs perfect above 5000. the fuel line is hooked directly to the engine. it has a electric fuel pump set at 5.5 psi. I have read the other threads the only thing I notice it doesn't have is a bulb. I prime it with the electric pump. the electric does run through the factory pump. I was out at the lake it started surging I turned on the electric and it did not improve. I would appreiate any help. thank You Joe

 

[hkeiner]

Re: 1986 Mercury 175 hp. part throttle Surge

I would check the fuel supply by following the below linked Mercury Service Advisory. It will show you how to test the fuel system using a vacuum gauge. This is a good way to find out if your bogging is due to fuel starvation. If the vacuum exceeds spec, then you need to figure out what component is causing it, eg, pluged vent, plugged screen in tank, leaking connections, etc.

http://www.marinepartsman.com/Mercury-Marine-service-bulletins/Mercury-Mariner/2001/EN_17.PDF

If the vacuum test does not show any problems, then I would next check the ignition system. I like to use a Smartach meter to easily monitor secondary voltage while the motor is bogging. If the meter shows that voltage is dropping during bog, then you need to figure out what component is failing using various bench tests described in the shop manual. If the voltage is not dropping during bog, then I would be perplexed and I would be asking for advice on this excellent forum too.

 

[Joe Sergi]

Re: 1986 Mercury 175 hp. part throttle Surge

Thank You for the great information Great site Thank You Joe