Mercury 4 Stroke Performance Issue

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HELP!

I just bought a new 2008 14' Ultracraft CT with a 25 hp Mercury 4 stroke tiller (power trim and tilt). It takes me about a quarter mile to get the thing on plane (alone or with 2 people)! It's terrible! My old 1986 25 hp Johnson on a 14' boat is up in 50 feet! I was told by the dealer that a "Doel Fin" would fix the problem?? Prop problem?? Any help would be greatly appreciated!

 

[foodfisher]

Re: Mercury 4 Stroke Performance Issue

Weight distribution?

 

[Trad]

Re: Mercury 4 Stroke Performance Issue

I don't think that weight distribution is the real issue, I had my buddy kneel by the trolling motor on the bow and it barely made a difference! It feels like I still have the trailer under the boat!

 

[TOHATSU GURU]

Re: Mercury 4 Stroke Performance Issue

You need a 9 pitch prop on that application....Maybe a 10 if you are both really skinny. And you also need to have the engine tucked for take off and then trim it out once you are on plane. Move the fuel tank to the bow and as much additional weight as you can.

 

[Moody Blue]

Re: Mercury 4 Stroke Performance Issue

You are running at near max HP for the boat so performance shouldn't be an issue. First things I would look at is ;

1) engine height - anti-ventilation plate should be level with or slightly above the bottom of the boat

2) engine trim - trim full down for best hole shot then trim up once under way.

3) prop - without a tach it's really difficult to determine the best prop. Too much prop and the boat is a slug and the engine lugs. Too little prop and you will over rev the motor. An experienced/competent dealer would be your best bet here.

Adding a fin is a band-aid solution to an unknown problem. It may help or it may create other handling issues. Try to find the problem first.

 

[Trad]

Re: Mercury 4 Stroke Performance Issue

I just raised the outboard up as far as I can. The cavitation plate is still about 1/2" below the boat. I took the boat out and what a difference. I wish I could have raised it another inch. The motor looks funny with the clamps above the transom though. I measured the transom and it is indeed a little over 20". The outboard seems to be more than a 20", is that possible? I don't really know what else I can do. The motor sure doesn't have the get-up-and-go that my old 2 stroke had but the top end seems to be close. The dealer told me to expect this with a 4 stroke.

 

[trendsetter240]

Re: Mercury 4 Stroke Performance Issue

I just raised the outboard up as far as I can. The cavitation plate is still about 1/2" below the boat. I took the boat out and what a difference. I wish I could have raised it another inch. The motor looks funny with the clamps above the transom though. I measured the transom and it is indeed a little over 20". The outboard seems to be more than a 20", is that possible? I don't really know what else I can do. The motor sure doesn't have the get-up-and-go that my old 2 stroke had but the top end seems to be close. The dealer told me to expect this with a 4 stroke.

Yes, it could be an extra long shaft (25"). What is the model number of this motor?

You could get a jack plate for the motor or sell it and replace it with a regular shaft outboard.

 

[TOHATSU GURU]

Re: Mercury 4 Stroke Performance Issue

Modern outboards are not 15", 20" or 25". That was a U.S. standard from years ago. Each brand and model are different, but they usually run anywhere from 1 1/2" to 1 3/4" longer than what they are marketed to fit.

 

[Trad]

Re: Mercury 4 Stroke Performance Issue

I just bought the boat. The model number is 1A25411FK

 

[trendsetter240]

Re: Mercury 4 Stroke Performance Issue

Modern outboards are not 15", 20" or 25". That was a U.S. standard from years ago. Each brand and model are different, but they usually run anywhere from 1 1/2" to 1 3/4" longer than what they are marketed to fit.

hmmm..really? So the new Evinrudes that are being sold here with 20" (308mm) shafts are actually longer? This is the first I've heard of this.

Besides..why sell them longer than advertised when 99% of the time motors should be mounted even with or slightly above the bottom of the hull? Longer than advertised shafts means more difficult mounting.

 

[TOHATSU GURU]

Re: Mercury 4 Stroke Performance Issue

Japanese engines have always been that way and since that Mercury is a Japanese design...Yes, really. As to why: The U.S. standard was arbitrary to begin with. The Japanese built for their own small domestic market at first and for whatever reason, that is/was their standard. When they began exporting to the rest of the world they never bothered to change their designs. I suppose that's because engines can always be raised up to achieve the correct placement. I'll take your word for the shaft length of the Evinrudes, but the other brands do not describe their engines has having an X" shaft length. What they say is that their engine is designed to fit an X" transom...Not quite the same thing, but for practical purposes correct.

 

[Moody Blue]

Re: Mercury 4 Stroke Performance Issue

I just raised the outboard up as far as I can. The cavitation plate is still about 1/2" below the boat. I took the boat out and what a difference. I wish I could have raised it another inch. The motor looks funny with the clamps above the transom though. I measured the transom and it is indeed a little over 20". The outboard seems to be more than a 20", is that possible? I don't really know what else I can do. The motor sure doesn't have the get-up-and-go that my old 2 stroke had but the top end seems to be close. The dealer told me to expect this with a 4 stroke.

Glad that worked out for you. The 4-strokes don't have the same bottom end grunt that the 2-cylces have so you will notice a performance difference in the hole shot. Could compensate for it with a prop that has 2" less pitch than your current one. You will loose a little top end speed and you will have to be careful not to exceed WOT specs.

With the motor sitting up high on the transom, be sure to bolt thru as well or at least use a safety chain. If you want to go higher then you will need a jackplate ($$$) or make your own fixed version with a few pieces of heavy aluminum angle. Others have posted photos in these forums in the past. Last option would be to trade you motor in for a shorter shaft model.