1986 Mercury 25XD won't plane or rev past 2k

[Rider]

I have the strangest problem with my 86 mercury 25XD. It revs fine in neutral, reverse, and forward when there is no prop on it. Put the prop back on and it revs to 5k in reverse and neutral but won't go past 2k in forward. Timing and carb settings are set properly, but for some reason when there is a load on the engine in forward, it won't budge. I rebuilt the carb, new spark plugs, wires. I compression tested the engine and its at 125 in both cylinders. I thought that it was a prop issue so I swaped out the props, same issue. I'm so stumped here, any one have any suggestions?

[capnzee]

Is the carb opening up to full throttle when in fwd-or is the timing advancing properly? -you may have screwed up the linkeadge.

[Rider]

No, the carb linkage is to full throttle, carb opens all the way, timing is set to proper spec at WOT, Would bad reeds cause this? It is when there is a load on the engine it won't rev, I didn't think it was reeds because fuel isn't spitting back into the carbs. I can see the fuel vapors, leaving the jet and it is the same in forward and reverse.

[njj502]

Does this have the shift on the throttle handle or on the side of the engine?

[half fast]

I would check the ohm. resistance on that stator.It is a two step style like the one found on the V 6 merc's. hf...

[njj502]

Is it still acting up worse in forward VS. reverse? Need to know this and if it's a shifter on the tiller handle.

[Rider]

It is remote so no tiller, I can see that when it is at WOT in forward and reverse, the carb and timing linkage move the same and travel the same distance. Would a bad stator cause it to not go over 2K RPM's in forward only and not reverse?

[njj502]

Are you just seeing the linkage move or physically seeing the throttle plate?

[Rider]

I am seeing both the linkages move and the throttle valve open all the way. I read somewhere once that the seals on the block start to go and when there is a load, air leaks in. But would that happen all at once? it was fine last month, not all of a sudden, nothing.

[njj502]

Something is screwed up between reverse and forward. I dont' seee what else could cause it.

[Rider]

I'm stumped, the things is, when I take the prop off, put it in forward and pin it, it revs to 5K like a beast. What would cause it to bog out when its under a load? My initial thought was bad gas, it was running bad, but it has fresh gas. Then I thought prop, so I changed out props, nothing, no change. I'm gonna let it warm up and do a compression test on it tomorrow. I even thought timing was off, but if I take the linkage off at WOT and move it back and forth, no change in RPM. Its running like timing is really retarded at WOT (not the motor, just timing). One final thought is that is it possible when I give it gas in forward with the prop on, it pushes the entire shaft forward into the case, causing it to bind? I drained the oil and didn't find any shavings in it. Ideally I would love to change out the lower unit with another 25XD and see if the problem continued.

[njj502]

Don't ever "free-rev" these engines like that. VERY VERY hard on parts like bearings and such. Like I said before it's something between forward and reverse. If it revs up good in reverse but not forward there is something going on. My guess is some sort of adjustment in the cables or timing or something of the sort. Really doubt it's in the lower but could be.

[richcraft]

Bottom end outer bearing housing loose??? I'd grab the guts behind the prop and check. Maybe a little pry in & out to see if it's loose.

Just a thought.

[njj502]

I think you should try to get a buddy's lower and try it just for grins but I still think it's in an adjustment.