Full Throttle Power Loss Questions

[jgevedon]

Guys, I've got a 01 Mercury XRS 150 that has been pretty much trouble free but I've got an issue that I'm concerned with right now. I've lost about 7 mph this year on top end with no apparent reason. Motor sounds good and has always run with no sputtering. Any leads or insight on this would be great. Just looking for a place to start as I'm definately no mechanic.

[Bair]

how is your prop ??? that would be one of my first ideas... next would be quality of gas may need to try an additive

[mhall]

Check your hub on your prop. Are you reving on RPM and not going as fast or have you also lost Rpm's.

[jgevedon]

My tack started acting up this year and at this point I'd call it unreliable. It doesn't sound the same on top end to me though. I did replace my prop hub assembly this year. Also had new plugs and compression check showed great. I've always used 89 in this engine and it's done fine. Is there a certain additive that I might should try? Thanks for the responses guys.

[RANGER519]

i would get my tach fixed first & check my rpms. you can add some sea-foam to gas tank & this will clean everything out good .but i would fix my tach first.



just my 2 cents worth ranger519

[Wormin]

When was the last time you have waxed the bottom of the boat,you can lose about that much with a dirty hull. Also Warmer water will slow a boat down alittle in the summer time. I lose about a 100 rpms in the summer.

[cblazer]

I had the same problem this spring and had anglers outpost run just about every test the knew to run and could'nt find anything wrong. Finally Mercury suggested doing a let down test on the cylinders and that was the problem. Had one cylinder that was bad. Had to get a total rebuild. That hurt the pocket book. Hope for your sake thats not the problem.

[buzzking]

Under NO, NO, NO, circumstances do you want to wax your hull. Sudden loss of speed could be a number of things. 1st thing, get your tach fixed, hard to identify the problem until we know where the motor is running. 2nd have you added a jackplate or messed with the throttle linkage any? Anyway your throttle linkage isn't opening all the way up? 3rd, plugs and wires, you said you replaced but did you replace with the right plugs? 4th, has you prop gotten ragged out around the edges? A good finished balanced prop can make 4-6 mph top end difference. 5th, compression let down test, may need an overhaul.

[Col Forbin]

I have heard the same thing about waxing the hull. It actually creates more surface friction. On another site they describe rubbing your finger across a piece of glass - it sticks and squeaks as it goes across, however, a peice of wood sanded with 400 grit paper will be as smooth as silk. Those microscopic scratches/pores in fiberglass actually collect air at high speed and cause the boat to glide. When you wax it fills those in creating an ultra smooth/sticky surface just like the finger on the glass analogy. High perfromance racing boats actually scuff the bottoms with a high # grit sandpaper to add speed. So buzzking is dead on Don't wax that hull, especially if you are trying to add speed.

[jgevedon]

I waxed it this year trying to pick some up but it didn't make any difference either way. Could an old fuel line or bulb cause this? Plugs were changed and compression checked at authorized mercury dealer. He said compression was really good for an 8 year old motor.

[Jbyrd]

Guys, I've got a 01 Mercury XRS 150 that has been pretty much trouble free but I've got an issue that I'm concerned with right now. I've lost about 7 mph this year on top end with no apparent reason. Motor sounds good and has always run with no sputtering. Any leads or insight on this would be great. Just looking for a place to start as I'm definately no mechanic.

It sounds like you have the summer blahs... ALL carb motors loose rpms/ speed during warm or more importantly humid conditions. Wait until cool days are here and if the problem doesn't fix itself it could be the carbs are a little lean.... good luck.... it also could be as simple as the throttle linkage not opening up all the way

[buzzking]

I'd say jbyrd probably has you diagnosed the closest, I usually run about 200 rpm or so lower in the heat and its worse with carb motors. 2nd, get something that will remove that wax off the hull and go run it and see what she does