Why is my 4 stroke such a dog?

I recently downsized my boat and wound up with a used Lund Rebel 1650 and a 25 hp Suzuki 4 stroke. I had a similar Lund Rebel in the past with a 30 hp Evinrude 2 stroke (1989). That rig did fine and had no problem getting on plane even with 4 aboard. It ran 24-27 mph depending on load. I expected a drop in performance and top speed but this rig is a dog. It takes almost a 1/2 mile to finally get the boat on plane with my wife and I aboard. Then it tops out at 18 mph. I expect to have 3 in the boat this weekend and I do not believe it will have the power to plane out the boat. The motor runs fine and has very few hours.

I had heard about the lack of power in the 4 strokes but did not expect it to be this bad. I had a 140 hp Suzuki 4 stroke and that ran with plenty of power. What makes for the different performance 2 stroke vs 4 stroke? Does not 25 hp = 25 hp? How big of a 4 stroke do I need to equal the performance of my old 30 hp 2 stroke?

What have you got for a prop on it?

You have to keep in mind a 25 horse 4 stroke weighs more than a 30 horse two stroke. Getting the right prop may help a little bit but not much. Also boats weigh more now than they used to.

It a 10 X 10 I believe.

I think that boat is rated max 40hp and I think you are just underpowered with the 25. .02

Torque.
Your 2 stroke had it.
Your 4 stroke doesn’t.

I needed to slow my boat done to troll with my 50hp 4 stroke. Sometimes I like to use the big motor and not my trolling motor.

I added a trolling plate and what a difference it made on how fast the boat planes. I could not believe how well the boat plained.

If you have the correct prop for motors rpm’s, check out a trolling plate or hydro foil as it could really help with the plaining of the boat.

I also picked up some rpm’s and a bit more speed.

Worked for me.

I am in the same “boat” as you. I just went from a Tyee with a 115 2 stroke to a Trophy with a 115 4 stroke. My Trophy weighs more than the Tyee and the 4 stroke weighs more than the 2 stroke. I just don’t get the same hole shot as I did with the old boat and motor. I have accepted my fate. I sure do enjoy the quiet clean burning 4 stroke though

A 25hp merc 4 stroke weights 172 pounds and a 25hp 2 stroke weights 75 pounds so do the math….

Woody

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A 25hp merc 4 stroke weights 172 pounds and a 25hp 2 stroke weights 75 pounds so do the math….

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Really? Wow, that is quite a difference!!!

You might try a 4 blade to get you on plane a little faster.

One thing you can do inexpensively that will help your hole shot is to add trim tabs. No need to buy them from cabelas/westmarine; go to TrueValue and buy a 48″ piece of 2″ aluminum L-angle. Cut it to fit your boat and silicone it in place. Let it cure for a few days, then test it. If it gives you what you need, then silicone/screw/bolt it in place.

I had a similar situation with a 25hp tiller on a 40hp rated hull. Could not get the boat to plane with any setting. Added about 80 sq inches of tab this way. Put me back in the middle of my pin range. Simple fix. Didn’t even have to remove any transducers. I get so much hole shot now, i even wish I’d only put 1/2 as much on.

Stu has it right. Tabs or a fin is the only way that nose comes up and planes. My buddy tried the 4 blade option on a 4 stroke, 4 cyl Merc 50. Nothing prop-wise offered him relief. Don, I don’t suppose you ever saw my 16′ Lowe with a 25 Suzuki on it. The fin is what finally got me to be able to plane.

Went throught the same thing. I had a 50hp 4 stroke on my boat and took forever to get on plane if it even would. Solved the problem though! NEW 60 hp E-tec. Works great. Oh yeah replaced boat also! Great motor!

Where do those trim tabs go? on the hull of the boat under the transom? On the planer plate on the motor?

This boat weighs like 625 lbs. and the plate says it is rated for 50 hp. I like many things about the 4 stroke and this is my single complaint. But it sounds like I need a bigger outboard. I was hoping to be legal for the 25 hp routes into the BWCA.

For Don

That should cure Don’s issues.

It is not unusual for an over propped 4 stroke to be really slow. What rpms at WOT?

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I am in the same “boat” as you. I just went from a Tyee with a 115 2 stroke to a Trophy with a 115 4 stroke. My Trophy weighs more than the Tyee and the 4 stroke weighs more than the 2 stroke. I just don’t get the same hole shot as I did with the old boat and motor. I have accepted my fate. I sure do enjoy the quiet clean burning 4 stroke though

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Now all you need to do is change your screen name

trim tabs: i glued mine on the back of the transom at the plane line to extend the ‘bottom’ of the boat an additional 80 sq in. i was amazed at the impact. it was like adding 15hp.

fins: will help also and can be used in combo. they will knock a bit off the WOT speed and gas consumption, but it’s not significant to me.

Conceptually, it’s like adding pods to the back of your boat like the mud motor boys do. Puts your mass further forward on the planing surface, i.e. easier to come up and out. For $20 it was a pretty phenomenal impact.

I have a 14ft boat with a 25HP four stroke Merc. Same problem. Added a hydrofoil which made a huge difference in the boat’s ability to get up on plane, although the top end speed did drop a little. The lower top end speed is still worth it to me in exchange for the improved overall performance in all other areas.

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One thing you can do inexpensively that will help your hole shot is to add trim tabs. No need to buy them from cabelas/westmarine; go to TrueValue and buy a 48″ piece of 2″ aluminum L-angle. Cut it to fit your boat and silicone it in place. Let it cure for a few days, then test it. If it gives you what you need, then silicone/screw/bolt it in place.

I had a similar situation with a 25hp tiller on a 40hp rated hull. Could not get the boat to plane with any setting. Added about 80 sq inches of tab this way. Put me back in the middle of my pin range. Simple fix. Didn’t even have to remove any transducers. I get so much hole shot now, i even wish I’d only put 1/2 as much on.

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X10.

This would also fix a chronic porposing problem.Some Lowe Roughneck jons have a similar set-up on their transom bottoms.Just bend it down a degree or so to keep the bow down.