Trouble holding trolling speed

[AFDan52]

I have a 1999 Yamaha F9.9 hp Kicker motor , I also have a 703 remote throttle control with electric start. I am having trouble holding my trolling speed . The motor runs fine for a few minutes and then it starts to bleed off or lose rpm's to the point of dieing. I've noticed that there is no vent on the fuel tank and I'm always having to open the gas cap to release the vacuum , I'm thinking that the vacuum might be the problem. Hoping to find a little help.

 

[Chad Flaugher]

That would be a perfect place to start. Try running yer setup with a loose gas cap, or just replace it. Next would be checking your filters. Always start simple and work your way up to the bigger stuff. Another good rule of thumb with trouble shooting, is to alter one thing at a time before testing. Don't mess around with a ton of things and hit the water hoping for the best. That way, you'll know what the problem was, and you can help all us other boaters here on the forums!

 

[steelespike]

As far as I know OMC tanks have a vent that opens when you connect the line to it. Don't know on the Yamaha.
If you had a venting issue the the primer bulb would collapse as the vacuum increases.
I do wonder about the fuel pump At slow speed it may struggle.I note the fuel pump is part of the carb unit.
Speaking generically If the diaphram leaked it may slowly flood the carb.If the pump is just weak squeezing the primer
bulb may solve the problem. If the vent was not working the bulb may just stay flat after you squeeze.

 

[Teamster]

I had similar problems with my 98 Merc kicker which I think was built by Yamaha and painted black,...

I ran some Amsoil Quickshot thought it and now it runs much better,...

I figured it was a cheap and easy thing to try,..

 

[fishrdan]

What type of fuel tank are you using? The new style low permeation EPA certified tanks have caused issues like you are experiencing, the tank not venting as gas is pulled out of the tank, causing a vacuum that the outboard can't pull against.

Do as Chad mentioned and loosen the tank's fill cap to see if that resolves the problem.

If I had a non vented EPA tank, it would mysteriously get vented................

 

[AFDan52]

Thank you all for your responses , I forgot to mention that the tank I'm using is one of the Non-Vented type Attwood 3-gal. fishrdan , I am adding a vent to this tank. I am going to be rechecking all of the connections and fitting from th tank to the motor. I will post my findings when i'm through.

 

[AFDan52]

Hi all, well you guys were correct , I need to vent my tank , but I found that I also needed to make some adjustments as well. The motor runs fine now, Thanks for your help.