90 Yamaha 2 Stroke Issues

[fishing coach]

I have a 2003 Yamaha 2 stroke 90.

If I run it wide open throttle (5,000 RPM) it will bog down in about 30 seconds to a minute. If I back off the throttle it will continue to run. If I run it at about 90 percent it will run as it should and neve bog down. I have changed plugs and removed all three carbs and cleaned them and put them back on. Ran it this morning with the same issues.

Has anyone had similar issues or any suggestions of things to try?

Thanks

[Red Beard]

I have a 2003 Yamaha 2 stroke 90.

If I run it wide open throttle (5,000 RPM) it will bog down in about 30 seconds to a minute. If I back off the throttle it will continue to run. If I run it at about 90 percent it will run as it should and neve bog down. I have changed plugs and removed all three carbs and cleaned them and put them back on. Ran it this morning with the same issues.

Has anyone had similar issues or any suggestions of things to try?

Thanks

I just had these similar issues on my outboard. There is a thread “Outboard Diagnosis” with different things I did to help.

Fuel issue it sounds like.
How old are the fuel lines?
Water in fuel?
Do you have a fuel separation filter? (Filter clogged)
Pinched fuel line somewhere?
Check/Replace spark plugs? (How’d they look?)
On the carb, are all butterfly valves in sync? (They all open and close together in unison.)


The cause for issue with my outboard was a pinched fuel line at the fuel pump. A hard bend would starve my OB at high throttle but allow enough fuel to flow at lower RPM’s. (80% throttle and less)

After upgrading my fuel lines the issue went away. Now she doesn’t like to idle, but I can live with that for now.

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[FTReelty]

I have a 2006 with a very similar problem. I can run WOT for about 8-10 minutes, alarm comes on, throttle down and wait about 90 seconds and alarm goes off-can resume operating at about 90% throttle and runs fine....Had everything checked a couple times and cant seem to find issue. Ive just accepted I cant run at WOT-or time to buy a new motor.

[Juan]

When is the last time you changed your water pump and thermostats? Is it running hot? I'm not sure about a 90 but I had a 150 once that had a safety feature that would reduce the rpms if it ran hot. If you have a worn impeller in the water pump it might not be pumping enough water at wide open to keep the engine cool.

[SCALAWAG]

anti siphon valve on your tank can cause this, it is a spring and ball located in the fitting on your tank where the fuel line hooks up. i took mine off and cut part of the spring off so as not to have as much spring pressure on the ball. solved my problem. this was on a 150 2 stroke. Just a thought

[STMU]

When is the last time you changed your water pump and thermostats? Is it running hot? I'm not sure about a 90 but I had a 150 once that had a safety feature that would reduce the rpms if it ran hot. If you have a worn impeller in the water pump it might not be pumping enough water at wide open to keep the engine cool.

Yep! I had the same problem on an older yamaha and it was a worn impeller. Would reduce rpms when it ran to hot. Would run fine until full throttle. Run for about 10 seconds and then bog down. Bought it used, and the guy told me changed it. Clearly didnt, but it made for an easy fix.

[Steve Stinson]

anti siphon valve on your tank can cause this, it is a spring and ball located in the fitting on your tank where the fuel line hooks up. i took mine off and cut part of the spring off so as not to have as much spring pressure on the ball. solved my problem. this was on a 150 2 stroke. Just a thought

Yep. Mud Dobbers in the fuel tank vent line will do this too. Is the squeeze ball in your fuel line collapsing when this problem happens or staying inflated? If it is collapsing, you could be pulling fuel out of the tank faster than air can come in. Normally, I've only seen older V6 outboards do this. The smaller motors don't burn fuel as fast.

- Steve Stinson