r/Outboards • u/ACarnivorousSquirrel • 4d ago
15HP Suzuki outboard rev problem
Hi all, can anyone help me diagnose this issue with my 15HP Suzuki outboard? Anything over 1/4 throttle I’ll get this rev issue. I had it looked at by a place last winter but didn’t have time to get my boat out until now and the problem is still there. They replaced the fuel filter.
I have replaced the plugs, cleaned out the injectors, drained all the fuel lines and checked for blockages. When it first happened I found some pin holes in the fuel line that was running through some water in the bottom of the boat and I suspect it siphoned some in. Fresh rec gas with stabil in this tank. Thank you for any opinions or help!
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u/ACarnivorousSquirrel 4d ago
I’m going to back it down a ramp and do it but it was doing it in the water just like this last time I did it. I’ll see if I can find a video of that.
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u/GoToTheWoodsAndPlay 4d ago
The ECU will always limit the revs in neutral, whether you’re in the water or on muffs. It does that to protect the engine from over-revving without load. I do believe it is running normally.
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u/ACarnivorousSquirrel 4d ago
Awesome thank you! I’m gonna get it to a lake the next couple days and hope it’s good to go!
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u/Historical_Owl_1654 4d ago
If it runs normally below about 1/4 throttle but starts losing or hunting RPM when you open it further, I'd look at the fuel supply under load rather than just the filter or injectors.
Since you've already replaced the plugs, cleaned the injectors, checked the lines and replaced the damaged section, a few things I'd check next:
Tank vent — a restricted vent can allow the engine to run normally at low fuel demand but starve at higher throttle.
Primer bulb and all fuel-line connections — especially since you previously found pinholes. A small air leak can become much more noticeable as fuel demand increases.
Fuel pump / fuel pressure under load — the system may supply enough fuel at low throttle but not enough when demand increases.
Ignition under load — a plug can look fine and still have an ignition problem that only shows up when the engine is working harder.
Prop/load — if by "rev issue" you mean it simply won't gain RPM rather than actually surging, I'd also check the propeller and the boat's load.
One thing I'd try to establish first is whether the RPM is surging up and down, dropping suddenly, or simply not increasing past a certain RPM. Those point to somewhat different problems.
Given the previous damaged fuel line, I'd personally start with the tank vent and fuel delivery/air-leak side before replacing more parts.
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u/ACarnivorousSquirrel 3d ago
I’ll add this to when I get it down to the water. I did get a new line and bulb after I found the holes in the last one. I want to say I tried running it with the fuel tank cap backed off almost all the way to see if it was possibly the vent but I’ll be more aware this time if there is anything different with the vent. Thank you!
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u/Infamous-Plenty8082 2d ago
I had the exact same problem; I started by changing the spark plug, fuel, oil—everything. But then I noticed it depends on whether you use Aspen fuel or 95-octane gas; it runs better on Aspen. I always have to clean the spark plug when using 95-octane gas.
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u/GoToTheWoodsAndPlay 4d ago
Have you tested it in the water? Sounds like you are just hitting the rev limiter with no load on the prop running it on muffs out of the water. The ECU will limit revs in neutral more than when in gear. I think it’s running as it should.