95 Yamaha 115 stalls & surges at 4000 rpm

[GUMBEAUX]

Just bought this boat & it runs fine except when it gets above 4000 rpm's. My mechanic has me on a waitng list and was wondering if anyone might have an idea of what I could check in the mean time. I'm thinking its fuel related, maybe the fuel line and bubble primer need to be changed, I've already checked the in line filter & it seemed fine.
I just found this forum & think it's wonderful

[TownsendsFJR1300]

1995 C115TXRT Yamaha Outboard CARBURETOR Diagram and Parts

Can you describe specifically what its doing at 4,000 RPMs? Will it run up to 5,500 at WOT?

There should also be an under the cowl fuel filter, check that.

An easy check, get to the float bowls on the carbs. On the bottom of the float bowls (see above link) are drain screws. Drain each bowl into a CLEAN container (I use a tuna fish can) and see what comes out. Your looking for water, any crap, etc. Any water will make the fuel look cloudy and eventually collect on the bottom of the can. You can squeeze the primer bulb to flush and also make sure it is indeed working.

Check all your fuel hoses going to the engine and check for ANY leaks.

You mentioned an "in-line filter". Their generally not used as a transom mounted filter is considerably better. This filter may be slowing / hampering fuel delivery to the engine especially at higher RPM's.

Also pay attention (best to pull and inspect) the fuel line you can access. Ethonol CAN break down the internal coating of fuel lines and it can literally clog up the next filter down stream. (I had that literally happen on a 2' piece of marine fuel line- found parts of it inside the under cowl filter)

[GUMBEAUX]

Thanks Townsends, The ethanol breaking down the fuel line was one of my concerns too. Not sure what WOT means but it will rev to 5,500 but it surges & stalls as if it would be starving for fuel.
The inline filter I was referring to is the one on the motor inside the cover & the fuel looked good to me.
I will ck the float bowls like you said & change all the fuel lines & bubble primer & get back to you.
I asked the previous owner if he ran nonethanol fuel in it & he said he didn't, that made me suspicious.
Thanks again

[TownsendsFJR1300]

Yes, WOT is wide open throttle.

The line that broke down on me was Marine grade Mercury brand when they re-powered my boat.... You could pull it out in long, kinda curly pieces....

Agreed, the higher RPM issue sounds like fuel related...

There should also be a rubber seal in the "under cowl cup filter".
You might remove the cup and check the o-ring, that its not broke/damaged, causing an air leak

[Jason2tpa]

Thanks to the pro advice from Townsend I was able to remedy a similar scenario with my '98 115. I couldn't get over 4k. I removed the carbs, did everything he suggested like in this post, but also cleaned all the jets (as he also suggested). That was the issue with mine. Both my high speed jets were clogged.

If you're comfortable removing carbs, remove jets--soak in cleaner to loosen debris then shoot compressed air through each one. Making sure you can see completely through. If you're not comfortable, have your mechanic do it. And while he's got the carbs out might as well install a new kit if it hasnt been replaced in a while.