At my whits end

[Aaron Lariscy]

This 7.5 Mercury is driving me crazy, I have fixed the water pump issues completely rewired it where the insulation was falling off the wire, rebuilt the carburetor completely and thought I had everything straight now its something else. :evil: At speed it bogs like you have let off the accelerator. Its still running smooth just not at WOT then it will jump right back to where it should be. First thought was trash in the carb but like I said it was just cleaned and rebuilt. Could it somehow be an electrical issue? First step tomorrow is to take the carb back apart and blow it out with carb cleaner and then I am going to install an inline fuel filter. Bounce some more ideas off me now because I am at a loss.

 

[crazymanme2]

Does that carb have the fuel pump built on it or is it separate?If it's separate did you rebuild the fuel pump?

 

[Aaron Lariscy]

Fuel pump is built on to it and it was rebuilt as well.

 

[Aaron Lariscy]

Just for some more info it starts on the first pull everytime and idles great. Even at throttle when its acting up I can drop to idle and it just sits there and purrs. If its not the carb what could it be electrical? I'm leaning on an electrical short because its just like someone flipped a switch.

 

[BOB350RX]

WHEN YOU ARE RUNNING AT WOT AND IT DIES TRY PUMPING THE PRIMER BULB, I THINK ITS FUEL RELATED, I HAD A 9.9 THAT DID ALMOST THE SAME AND I REPLACED THE FUEL LINE FROM TANK AND FIXED IT, I IT HAD SWELLED AND WASNT ALLOWING ENOUGH TO SUPPORT WOT FOR ANY DURATION, HOPE THIS HELPS

 

[Aaron Lariscy]

That was the first thing I tried but it doesn't help thanks for the suggestion though.

How about this little tidbt yesterday I had it at 3/4 throttle and it was bogging like I explained. I reached up and turned the cam follower to open the butterfly to WOT and nothing changed at all. Seems like it should have flooded out unless something was restricting the flow of gas correct?

 

[BOB350RX]

that would be my thoughts, hows the vent on your tank? fuel lines?im just running over this in my head it my just be the carb, main jet?

 

[Aaron Lariscy]

Tank and lines are brand new vent is a screw on top of the fill cap and should be fine. I took the carb off yesterday and there was trash in he bowl I cleaned it out and that's as far as I went I'm going to give it a more thorough cleaning this afternoon and change the plugs. I hope that fixes it and I don't have an electrical gremlin.

 

[BOB350RX]

being there was junk in the carb i would have to believe that it is your problem, hope you get it going, my 9.9 has a screen the fuel hits b4 it gets to the pump make sure you done have anything there also, not sure if you motor has the same set up but worth a check, i had a prob with that as well in the past

 

[Aaron Lariscy]

This one does as well I hope I get it ironed out as well I want to be fishing

 

[Aaron Lariscy]

Ok cleaning the carburetor and installing a fuel filter didn't help here are some more observations.

Could a set of bad points be causing my issue? They looked pretty corroded, I sanded them alittle but they still look rough.

I pulled the plugs and looked carefully at them, the top one appeared normal with what looked like carbon buildup on it, I sanded it off and put it back. The bottom plug was entirely different it was shiny new looking but had what looked like motor oil all over it I have no clue what that could be or where it's coming from.

What's the deal with timing this little motor it has some jibberish on top of the recoil starter about timing at TDC how do I go about checking this?

Other than that everything looks good, today I had it running pretty smooth at 3/4 throttle but as soon as I attempted to go to WOT it would start cutting up.

 

[flintcreek]

Have you confirmed that it is firing on both cylinders? Sounds like it may just be hitting on one cylinder...does it ever run WOT? These little 2 cylinders will run smooth on just one cylinder.

Flintcreek

 

[Aaron Lariscy]

Have you confirmed that it is firing on both cylinders? Sounds like it may just be hitting on one cylinder...does it ever run WOT? These little 2 cylinders will run smooth on just one cylinder.

Flintcreek

I unpluged the cylinders one at a time today and it got alot rougher but I could only perform such a test at idle and not when its acting up at speed is there some reason it would only miss on a cylinder at speed and not at idle?

And yes it will run at WOT but only for brief moments.

 

[Aaron Lariscy]

How the heck does a set of points cost 109 dollars for this motor?!! And the condenser is not even available any longer! This thing is the biggest piece of crap I have ever owned or heard of!

 

[BOB350RX]

HAVE YOU DONE A COMPRESSION TEST ON THE CYLINDERS? SOUNDS LIKE YOU HAVE A BASKET CASE IM OUT OF IDEAS #-o

 

[nomowork]

A high speed "miss" could be bad spark plugs, plug wires, points, etc. Maybe try to run it in a barrel of water at high speed in the dark and watch for any sparks jumping from the plug wires. To help along, try running a screwdriver along the wire pointed at a ground source on the block and see if a spark jumps that gap.

 

[spg]

You didn't say what year the motor is but try this https://www.sterndrive.info/mercury-outboard-parts/points_condenser.html

 

[nomowork]

How the heck does a set of points cost 109 dollars for this motor?!! And the condenser is not even available any longer! This thing is the biggest piece of crap I have ever owned or heard of!

I think you could convert it to electronic ignition (pointless). I bought a 15hp Evinrude that the previous owner converted it to CDI. Points being out of adjustment could cause all kinds of performance problems. To set points correctly, a dwell meter is needed along with feeler gauges.