Outboard engine issue - help please

[Rascally]

Good evening fellow cruisers. I need help troubleshooting my outboard engine.

I have a Yamaha 30HP two-stroke outboard engine, model 30HMH.

It was purchased new in January 2022, and has run without any troubles. We use it several times per week, so it’s doesn’t sit unused. On average we go through a 5 gallon tank of fuel every two or three weeks.

Today it started but I noticed it didn’t sound the same, running rough, if that makes sense. When I tried to load it, it seemed to have no power. It wouldn’t rev-up much. Sounds like it’s bogging down, a term I’ve heard used when a car is shifted into a gear that’s too high for the speed of the car… the engine doesn’t have enough power and sounds “bogged down”.

There is also some sputtering, like it was out of fuel. There was a few strange misfires, which made me wonder if the fuel has water in it.

My troubleshooting thus far is described below, which has not revealed the problem.

Spark plugs, a bit oily and some carbon, but otherwise good. I cleaned them up and used a bit of emery paper to be sure the electrodes were clean.

I dumped the fuel and installed new, checking for any evidence of water or dirt - none found.

I checked the fuel filter on the engine and saw very tiny particles, but nothing significant. I checked the filter for minor tears, none found.

I disassembled the diaphragm fuel pump, and it appears fine, with the metal flaps looking perfect, and the diaphragm intact, not ripped.

I opened the carburetor and remove the float and needle, which look perfectly new - no wear, debris, or accumulation of anything. The entire carburetor looks like it’s never been used - whistle clean. I could see micro holes in the round chamber where air flows through, and there’s zero trace of any accumulation or gunk (like from ethanol fuels). Probably the fuel I’m using in the Caribbean is not EPA compliant and isn’t susceptible to gunking up the carburetor. I didn’t disassemble further.

I confirmed proper functioning of the choke and its linkages and the throttle and its linkages.

I’ve tried using the fuel-line pressure bulb to add fuel pressure while running the engine under load, and there was no improvement. The engine cannot deliver much power, and it seems to me that even under zero load the RPM acceleration is hesitating. I also feel the engine is not running as smooth as it used to when at idle or higher RPM’s. Seems to shake a bit more than I remember.

I don’t have a compression gauge, but I think this is my next step. I also think it might be worth replacing the fuel pump even though it seems to be fine (complete disassembly for inspection was conducted).

Obviously I’ve missed the troubleshooting steps that will eventually diagnose this issue. Hopefully those with experience or expertise can suggest next steps.

Sincerely,

Randy

[Lee Jerry]

Not exactly my best topic, but I agree with you that it sounds like a fuel delivery issue. Either a blockage or a leak. I assume you don't see any fuel leaking out, but there could be air leaking in. Have you tried changing the fuel hose from the tank to the engine? A blockage could also be in the fuel tank / pickup tube.

[Rascally]

Originally Posted by Lee Jerry

Not exactly my best topic, but I agree with you that it sounds like a fuel delivery issue. Either a blockage or a leak. I assume you don't see any fuel leaking out, but there could be air leaking in. Have you tried changing the fuel hose from the tank to the engine? A blockage could also be in the fuel tank / pickup tube.

Thank you. I don’t think it’s a blockage, because the inline hand pump successfully supplies huge volume of fuel to the carburetor. Unless that’s not a good test.

But the idea to replace the fuel hose is good. I’ll grab a new short fuel line to have as a spare, and see if bypassing my existing hoses makes a difference. 👍

[thinwater]

Originally Posted by Rascally

Thank you. I don’t think it’s a blockage, because the inline hand pump successfully supplies huge volume of fuel to the carburetor. Unless that’s not a good test.

But the idea to replace the fuel hose is good. I’ll grab a new short fuel line to have as a spare, and see if bypassing my existing hoses makes a difference. 👍

You looked in the carb but did not pull the main jet. If it is clogged you will have to poke it out with a wire. One of the more likely problems. It can come suddenly, with one tiny spec of dirt.

[Rascally]

Originally Posted by thinwater

You looked in the carb but did not pull the main jet. If it is clogged you will have to poke it out with a wire. One of the more likely problems. It can come suddenly, with one tiny spec of dirt.

Can a particle make it past the filter that’s on the engine? That’s a very fine filter…. and I’ve inspected very carefully for a rip or hole in the filter, and it looks good.

I agree that I’ve not ruled out the carburetor. My decision was that I might make things worse by messing around with a complex device. I’m unsure if removing things that have been “set up” in a carburetor will result in a poorly setup carburetor when I reassemble. I need to see directions on how to reassemble and properly adjust the settings. (I assume all those little screws can be setup incorrectly).

[Kettlewell]

Clean the carb jets as Thinwater said. You might be able to blast them out with the little thin red straw that attaches to a can of WD-40, which I have done many times. It just takes the teensiest piece of crud to plug a jet up. Start using the blue marine Stabil 360 in every tank of gasoline. I add it when I add the two-stroke oil. Make sure you are using a quality, name-brand two-stroke oil in the proper quantity. The plugs should be replaced at least annually. Don't fiddle around with cleaning them--just replace with the proper ones. To help avoid problems install a filter between the tank and the engine.

[Tin Tin]

Put in new spark plugs - that eliminates one issue. Cleaning up old ones has a 50:50 chance of success.

[Rascally]

Originally Posted by Kettlewell

Clean the carb jets as Thinwater said. You might be able to blast them out with the little thin red straw that attaches to a can of WD-40, which I have done many times. It just takes the teensiest piece of crud to plug a jet up. Start using the blue marine Stabil 360 in every tank of gasoline. I add it when I add the two-stroke oil. Make sure you are using a quality, name-brand two-stroke oil in the proper quantity. The plugs should be replaced at least annually. Don't fiddle around with cleaning them--just replace with the proper ones. To help avoid problems install a filter between the tank and the engine.

This is great advice that I needed to hear. My maintenance hasn’t been this attentive. Thanks!

[Rascally]

It was the spark plugs.

Thanks to all for your quick replies and suggestions.

Where I’m located I couldn’t get spark plugs easily, but I’ve got them now, and that was the issue. I thought it was a fuel problem… but nope. I have much to learn! ��

Again, thank you all for your input. This group of collective knowledge is fantastic.

[ChrisJHC]

Originally Posted by Rascally

It was the spark plugs.

Thanks to all for your quick replies and suggestions.

Where I’m located I couldn’t get spark plugs easily, but I’ve got them now, and that was the issue. I thought it was a fuel problem… but nope. I have much to learn! ��

Again, thank you all for your input. This group of collective knowledge is fantastic.

Hopefully you bought a spare pair at the same time!