Yamaha outboard RPMs jumping

[Rusty5387]

Thanks everyone! I am judging it based on sound and on my tach. I will see if I can find a prop to test with before I go out and buy one. The other thing that was brought up to me was to make sure when we installed the new lower unit that it had a ventilation ring already installed or was I supposed to transfer that from my old lower when I took the prop off. A friend of mine had an issue with their ventilation ring and it caused the same issue on their outboard. Fingers crossed that's but I won't be able to check until sometime tomorrow.

[phatdaddy]

I was just asking because a wacky tach is also a symptom of electrical/charging issues.

[THEFERMANATOR]

Make sure the shift linkage is adjusted correctly. Not sure on the yamaha, but on OMC's you have to set the shift shaft height. If you don't get it correct, it will jump out of gear like you describe, and it trashes the clutch dog when it does it. Also on that vintage yamaha, make sure the shift shaft isn't rusted out to nothing. They can rust to the point tbey twist, and not hold it in gear.

[Rusty5387]

I appreciate all the help guys! At this time I am pretty sure its the ventilation ring. I spoke with the company I got the new lower unit from and they confirmed it did not come with a ventilation ring and I checked the old lower unit and it has a ventilation ring on it so I just need to figure out with ventilation ring I need and where I can purchase it from. Once I install that I will update if it fixed the issue or not.

[Rusty5387]

Okay I believe the problem is solved. It was not the prop and there is no such thing as a ventilation ring for a Yamaha outboard. Before launching the boat this spring I added an underwater light that I've been wanting to add for a few years now. Instead of purchasing a light that I would have to mount to the transom I opted for a light that screws into your existing drain plug. The light worked great, was very bright even in the darker water in the river near me and attracted bait fish to the boat almost immediately. I realized that is the only thing I changed on the boat this year prior to having the issue. We pulled the boat out and it looks like the light sticks out just enough to mess up the clean water flow that should be going right to the prop. I removed the light and put the regular drain plug back in and took it our for a quick run. The boat got on plane much quicker and ran great. I could not get it to ventilate again or a jump in the rpms. I appreciate the advice from everyone that replied but turns out it was my own fault. tight lines guys

[Destroyer]

Originally Posted by Rusty5387

Okay I believe the problem is solved. It was not the prop and there is no such thing as a ventilation ring for a Yamaha outboard. Before launching the boat this spring I added an underwater light that I've been wanting to add for a few years now. Instead of purchasing a light that I would have to mount to the transom I opted for a light that screws into your existing drain plug. The light worked great, was very bright even in the darker water in the river near me and attracted bait fish to the boat almost immediately. I realized that is the only thing I changed on the boat this year prior to having the issue. We pulled the boat out and it looks like the light sticks out just enough to mess up the clean water flow that should be going right to the prop. I removed the light and put the regular drain plug back in and took it our for a quick run. The boat got on plane much quicker and ran great. I could not get it to ventilate again or a jump in the rpms. I appreciate the advice from everyone that replied but turns out it was my own fault. tight lines guys

Like the saying goes, you're never too old to learn new tricks. First, congratulations on figuring out the problem and second, thank you for sharing both the problem and the solution with all of us. I've never heard of something like that before, but you can bet that I'll keep it in mind if I ever want to mount an underwater light off the stern of my boat. Once again, thanks

[Pipe_Dream]

Wow, that's a new one on me. Glad you figured it out!