Mercury 175 hp no WOT

[walleyemanII]

The engine runs fine up to about 3500 rpm but will not go above without surging. When you back off the throttle it will run find. I have rebuilt the fuel pump, replaced the fuel filter in the engine and fuel filter/water filter by the build in tank. I have checked the vent on the tank and it is open. I have replaced the tempo fuel line (failed) from the engine inlet to the filter on the engine. I have checked the carbs by removing the plugs by metering jets onthe first carb and it appeared to be clean. I have done a visual inspection on the stator and cleaned all of the button connections. The 2 voltage regulators have been replaced prior to me acquiring the boat and motor. The engine ran fine at first. I have burt off all of the old fuel and have added at least 2 treatments of fuel conditioner from stabil in the fuel. I have also replaced the plugs.

My need thing to check would be the fuel line from the tank to the motor then the tear down one of the carbs to check for contamination. I would not expect the carbs to be bad if the inline fuel filter did its job.

Am I going the right direction or should I check out the cdi packs?

 

[walleyemanII]

Re: Mercury 175 hp no WOT

The engine is a 1993 v6 with carbs and cdi packs

 

[j_martin]

Re: Mercury 175 hp no WOT

The engine runs fine up to about 3500 rpm but will not go above without surging. When you back off the throttle it will run find. I have rebuilt the fuel pump, replaced the fuel filter in the engine and fuel filter/water filter by the build in tank. I have checked the vent on the tank and it is open. I have replaced the tempo fuel line (failed) from the engine inlet to the filter on the engine. I have checked the carbs by removing the plugs by metering jets onthe first carb and it appeared to be clean. I have done a visual inspection on the stator and cleaned all of the button connections. The 2 voltage regulators have been replaced prior to me acquiring the boat and motor. The engine ran fine at first. I have burt off all of the old fuel and have added at least 2 treatments of fuel conditioner from stabil in the fuel. I have also replaced the plugs.

My need thing to check would be the fuel line from the tank to the motor then the tear down one of the carbs to check for contamination. I would not expect the carbs to be bad if the inline fuel filter did its job.

Am I going the right direction or should I check out the cdi packs?

Two areas to look at are:
1. Fuel pressure. Requires rigging a temporary 15 psi pressure gauge to the last unused 1/8 inch carb fuel rail, probably on the bottom carb. Needs to stay above 2 lbs and under 7 at all times.

2. Stator charge coils. Measured at the switchboxes while cranking with a DVA and compared to a chart, either in the manual or on CDI's website. If the bug is solid, it might show up with ohmmeter readings.

hope it helps
John

 

[walleyemanII]

Re: Mercury 175 hp no WOT

I opened up the fuel line before the primer bulb and you could not even see through a 7 inch section due to the residue from the plastic liner. Not good

 

[walleyemanII]

Re: Mercury 175 hp no WOT

This what a failed hose looks like. No fuel to the bulb from this hose

 

[walleyemanII]

Re: Mercury 175 hp no WOT

Found more hose from the fuel/water seporator to the bulkhead that was made by mercury with the same failed condition. The hose is just not made for the newer fuels.

 

[walleyemanII]

Re: Mercury 175 hp no WOT

This motor came from salt water. I was running on the lake last night and the rpms went up to 4500 then it shut down but would restart right away. Replacing the fuel lines fixed that problem. What I did notice when I restarted the motor that almost steam was coming out the rear water discharge port. I decided to check the thermostats and found what years of salt water use can do. Replace the stats

 

[walleyemanII]

Re: Mercury 175 hp no WOT

I replaced the thermostats and had a complete meltdown of the water pump. Makes me wonder about the muffs

 

[chum1]

Re: Mercury 175 hp no WOT

here is an idea if you can find a plastic 30 gal. barrel, this works good for me and also allows running in gear for short periods.

 

[walleyemanII]

Re: Mercury 175 hp no WOT

Great idea. This allows you to dump the barrell with out any problems

 

[walleyemanII]

Re: Mercury 175 hp no WOT

I used the muffs again but make sure their was water coming out of the water vent holes just above the cavatation plate. IF the water is flowing out the small holes then the lower water chamber is full of water. I also replaced the poppet valve assembly after reading a few other posts then after openning up the valve it was corrided shut. Salt water plays havic on salt water motors that have sat for an extended period of time. I also found a few good videos on youtube that show you how to. I posted a photo of the boat that I am working on

 

[walleyemanII]

Re: Mercury 175 hp no WOT

After replacing the poppet valve and a trip to the lake it appears that all is well now. It ran for around 4 hours with no shut downs. It appears to be fixed

 

[walleyemanII]

Re: Mercury 175 hp no WOT

Trip to lake this past weekend and the motor ran fine. Trimed out at 5000 rpm and running 38mph on the gps. Its been a slow process but thanks for the help