1993 classic mercury 2 stroke 4 cyl bogging down

[MuskyRookie]

My motor is bogging down at full throttle but not until I reach 25 mph, rpms reduced in half as well as speed. When I try again it works fine until I hit 25 mph and the problem repeats.

I have new spark plugs, leakdown @ 6% on all 4 cylinders, spark test good, cylinder drop test ok, both carbs flowing fuel, new impeller and removed carbon buildup in exhaust tube that was plugged but the problem remains.

Would switching to non-oxy fuel make any difference or does anyone have any ideas on what to try next?

[BoxMN]

Is it NEW (and I mean NEW) gas? Non-oxy shouldn't matter as long as the oxy gas is truly new, though non-oxy is better all around.

If running that motor from a 6 gallon tank, make sure the screw vent is not tight. Simplest thing to check for, and easiest to overlook. Good luck.

[boatfixer]

Simply switching to non oxy will not solve your problem, there is something else going on.

My first thought is the fuel supply side of things.

Things to consider:

Air leak somewhere in the line

fuel pick up in the tank may be dirty

**dirty fuel filter**

fuel pump failure

Have you tried choking/priming when this happens? By this I mean tapping in on the key.