67 merc 9.8 bogging at full throttle!!!

[Rodman738]

My 1967 merc 110 runs fine up to 3/4 throttle. When you try to go to full throttle the motor boggs instead of speeding up.
Anyone have any opinions? Fuel or ignition? Have replaced diaphragm in fuel pump and replaced fuel lines, new plugs.

 

[tpenfield]

One thing to try is see if you adjust the carburetor mixture to be a bit more rich. IIRC, there are a couple of mixture adjustments on the carb.

 

[Rodman738]

No Title

There is low idle adjustment screw, it doesn't seem to affect it!

 

[DeepCMark58A]

Check the fuel filter or fuel screens, sure sounds like it is not getting enough gas in the carbs.

 

[Rodman738]

The screen in carb is clean, I need to take main fuel orphice and check it or replace it. Is there a screen in fuel pick up in tank? It is a original mercury 3 gallon tank. Thanks for any advice!!

 

[DeepCMark58A]

Yes there is a screen in the tank, pull the 4 screws very easy to do.

 

[jimmbo]

I need to take main fuel orphice and check it or replace it. QUOTE]

I have never seen an Orifice become defective, I have seen them plugged, and I have seen them scratched, nicked and damaged by poor cleaning techniques. The latter is about the only reason(s) an orifice would need replacing. Solvent and compressed air is all that is needed to clean 99.99% of them. Poking drills, nails, pins, pipe cleaners, etc is a sure way to pooch the orifice

It sounds like you are experiencing a fuel delivery problem, probably dirt/gum/varnish somewhere in the fuel system.

 

[Rodman738]

Tonight I disassembled carb completely cleaned everything which I didn't find hardly any dirt. I also traded lines (inlet fuel to fuel pump and the fuel pump to block line) I must have switched them when I originally replaced both lines. I don't like the look of the new needle and seat it seemed like it kept sticking closed . I rounded the edges a little with some sandpaper which seemed to help a little. After reassembling everything and dropping it in the drum it seemed to run at full throttle. Hopefully I can get it on lake tomorrow and see what she do!!! Thanks for all your advice hopefully some of my experiences can help someone else.

 

[Rodman738]

Back to the drawing board!!! Does anyone need a boat ️ As soon as it got on load behind boat it went back to bogging out past 3/4 throttle

 

[jimmbo]

Still sounds like a fuel starvation problem. Air leaking into line prior to the fuel pump. Restricted fuel lines. Old fuel lines deteriorated internally and acting as check valves. Defective fuel pump, plugged fuel filter, plugged pickup in fuel tank

 

[Rodman738]

I noticed when I removed fuel line and left motor running that a little fuel came back out of the fuel hook up. It seemed to have a little air pressure behind it. I'm wondering if there is a faulty check valve? All screens are clear,everything seems to be clean. I replaced fuel lines in motor. It seemed to run fine at home in a drum of water. But on the boat it had the original problem.

 

[tpenfield]

You mentioned that you replaced the diaphragm in the fuel pump, but did you replace the check valves? I think there is a fuel pump kit that has both the diaphragm and the check valves.

 

[Rodman738]

No Title

I only changed diaphragm! I will definitely look into the check valves!!


Happy Boating!! Rodney Leesville Lake Ohio️️

 

[Rodman738]

Finally figured out YouTube! Is there a secret to changing check valves? what is best way to remove and replace? Are they pressed in or screw in?

 

[tpenfield]

Pretty simple to replace them. I answered your PM on the subject. I *Think* I have a thread here somewhere about rebuilding the fuel pump.

 

[Rodman738]

I did change the check valves but still had issues. Figured out lower cylinder did not have spark. Swapped coils there was no change . Swapped condensors then I had spark. Took the boat out today ran perfect for 20 minutes then I lost spark in upper cylinder. Going to order a new condensor and will probably put new plug wires on while it's a part.
My mistake was not checking spark in both cylinders. This motor had been running on one cylinder since I've had it.
Hope this saves someone some time on there motor! Wow what a tremendous difference when it was running on both cylinders.