Suzuki 2 stroke 4hp not delivering more power over 1/2 throttle

[Franziska]

Not really, the engine did see hardly any use until we bought it. It still looks like brand new under the hood.

As we are not full-term cruising at the moment I guess carb problems are likely.

[a64pilot]

I’m hoping carb, cause that can be fixed.
As carbs are so problematic you may decide to buy a spare and overhaul / clean this one and put it in spares, it’s what I do with freshwater pumps as they don’t last as long as I’d like.

Did you look to see if the magneto coil moves?

[Cpt Pat]

I had exactly the same problem with my 4-stroke. It turned out it was a damaged propeller. The bad prop was producing so much cavitation that the engine couldn't turn it above half-throttle RPM.

I replaced the prop, and the problem was solved.

Check your prop. If the paint is gone, or it has dings or anything wrong with the blade leading edges, it'll waste energy in cavitation, making it harder for the engine to spin. I now carry a spare prop so I can do an on-the-water repair if I strike it on anything. We have lots of crab pots here. It's a minefield out there!

[URL="

[TrentePieds]

Hello Cpt. Pat

Does that look better :-)? You might like to check your posts with pics/videos inserted before you pull the lanyard. The problem was just that the URL was cited twice. You might have "misclicked yourself", or it coulda been a machine/programming glitch. If you see the URL repeated, just remove the unwanted instance using the delete key on your keyboard.

My pleasure :-)!

TP

[Brewgyver]

Franziska,
I don't think you answered about whether or not this is a new issue?
From your initial post, I think this has been a problem for as long as you've had it. So I'm thinking there's a good chance that the motor is simply overloaded. A64 mentioned one possiblity, being over-propped. And even though the manual for the motor only lists 6, 6.5 and 7 inch pitch choices, it's still possible that it has the wrong prop installed. Many different makes and models of small outboards share the same output shaft size, and the previous owner could have replaced a damaged prop with one that fit, but wasn't right for that motor. Prop damage is very common on fresh water outboards from operating in shallow waters, rivers and streams.

Another definite possibility is that 4 hp is simply big enough to move your dinghy faster than speed at which the motor no longer seems to advance. What type is your dinghy, how much does it and its contents weigh?

And lastly, is your bottom clean?

[Franziska]

Hey, yes it's like this since we have it.

Bottom is clean and prop is ok.
Pretty sure the prop is the one which came with the engine. Most people never bother changing the prop.

I will definitely look into this if it's not the carb or any of the other issues mentioned above.

One thing I will do next time I'm on the boat (which be unfortunately in a long while) is run it in a tank to see if it sounds "choked" too.
Will only try this for a short moment.

Dinghy is a Spindrift 10 with a Laser deck & Radial rig.
Unfortunately she turned out a fair bit heavier than planned, as I added a layer of glass without reducing the plywood thickness. Still in general the dinghy is serving us well.

See https://www.ladyrover.com/photo-logb...y-in-france-1/
for pix.

Still I do have the impression it's not the weight or size of the dinghy causing this. In that case you would feel more power going into the water, which is not the case.

Thanks for the thoughts.

[Cpt Pat]

Originally Posted by TrentePieds

Hello Cpt. Pat

Does that look better :-)? You might like to check your posts with pics/videos inserted before you pull the lanyard. The problem was just that the URL was cited twice. You might have "misclicked yourself", or it coulda been a machine/programming glitch. If you see the URL repeated, just remove the unwanted instance using the delete key on your keyboard.

My pleasure :-)!

TP

(Sorry folks. This "sysop" conversation shouldn't appear in this thread - but now that TrentePieds has put it here...)

I obviously "checked before pulling the lanyard" - or I wouldn't have reported the problem.

The link only appeared once on my end. And the "Insert Link" selection was greyed out, preventing its use. I suspect the problem was/is server-side. Trust me, I know how to use the delete key. My choice was to delete the one occurrence of the link appearing to me and have nothing, or leave it and see a double entry. I repeated that effort several times.

This is a Layer Seven (application) problem - not a Layer Eight problem (problem between the keyboard and chair). Blaming Layer Eight for Layer Seven issues only curtails Layer Eight's free production of content on the your site.

You could give me permission to edit the source HTML, and then I won't disturb your slumber and invoke your snarky comments.

If you reply, please reply by PM to keep this irrelevant conversation out of the active thread.

[Franziska]

Well, resurrecting an old thread.
As we did not get the carburetor out the last time around (I know, I know...).

I did get it out this time, and I feel you guys were right.
Much to my dismay I discovered that someone previously pinched the tiny tube inside, probably in an effort to pull it out.

The brass screw looks messed up by someone else's previous attemptd and I can not turn it either (maybe someone has an idea how to loosen it?).

I did now widen the tiny copper tube a little as to at least restore full flow.
Picture shows it after widening.

It's frayed now but that is likely less an issue than when its diameter is reduced.
See attached.

Added info upon assembly, the bleed screw seems to cap the copper tube fully, so the fraying/widening does not work.

Will see how it behaves when put back together.

As we may eventually need a new carburetor, maybe someone can suggest which exact model this is based on the numbers on the attached images.
Additional there is the number 5ninside the chamber.

Thanks, Franziska
Attachment 260896

[Franziska]

It's all cleaned, the only thing which seems visibly off is that tube terminating in the cap screw which holds the bowl.
What is that tubes function?

[capt jgw]

OP hasn't said what kind or size dinghy it's on. 4hp is pretty small, maybe too small for the boat. I've had 2 and 3.5 hp motors that acted like this right out of the box. Too small for the boat if you wanted to go fast, but fine for slower speeds. I bought them for thier low cost and light weight, not speed potential. This would be similar to being over propped. The motor doesn't have the hp to get over a certain boat speed, it just sits there at that rpm no matter how hard you turn the handle. A smaller prop might help if there's one available.

[Franziska]

Originally Posted by capt jgw

OP hasn't said what kind or size dinghy it's on. 4hp is pretty small, maybe too small for the boat. I've had 2 and 3.5 hp motors that acted like this right out of the box. Too small for the boat if you wanted to go fast, but fine for slower speeds. I bought them for thier low cost and light weight, not speed potential. This would be similar to being over propped. The motor doesn't have the hp to get over a certain boat speed, it just sits there at that rpm no matter how hard you turn the handle. A smaller prop might help if there's one available.

OP here [emoji846] 3.20m rigid dinghy. Slightly overweight 45kg.
Problem is we even feel this Suzuki 4DT 2stroke is quite heavy to handle with 21kg for 4hp...
Haven't seen any lighter 6hp though..

[Sailmonkey]

Originally Posted by Franziska

OP here [emoji846] 3.20m rigid dinghy. Slightly overweight 45kg.
Problem is we even feel this Suzuki 4DT 2stroke is quite heavy to handle with 21kg for 4hp...
Haven't seen any lighter 6hp though..

Just reduce the prop pitch and you’ll have more success with the 4hp.

[GreenWave]

A 4hp outboard has zero chance of getting a dinghy that heavy up on plane. You may get some improvement if you sort out the carb issue ( if there really is one), but that won't get you all the way there. Your prop is bogged down due to weight and you have limited options. I posted those in your other thread.

[Franziska]

So, it's been a while, but I thought I provide some feedback.

We had the carburetor revised and changed the prop to a lower pitch one.

The choking is gone and the same hard dinghy planes now with 7-8kn.
It never did that previously.

Same 4hp Suzuki.

Very pleased with this.

I just update both old threads to help anyone having similar issues.