2006 Yamaha 90 HP 2 stroke stalling at idle

[md544600]

Good afternoon let me start with some background on this engine. This engine is mounted on a glastron 16 foot fiberglass boat. This boat belonged to my grandfather and when he past away he left it to me. This engine has not run in 7 years and has just been sitting. I started with the basics I cleaned the old fuel out of the fuel tank, cleaned the carburetors and tried it. I couldn't get it to run. It would fire with a shot of quick start and if I played with the butterflies enough I could keep it running but it was running very poorly. No throttle response it just bogged. So I elected to replace the fuel pump remove and clean the carburetors again and I replaced the fuel lines to everything. I also replaced the primer ball and the clip and that attaches the fuel line to the engine. I still had the same problem but it had slightly improved. I decided to add a water separating fuel filter to the unit and added more fresh gas. I have finally gotten it to run so I elected to put it in the lake and give it a good run thinking this would help with everything. It has great throttle response now and runs fantastic at anything above an idle. However if i return to idle after 15 to 20 seconds it stalls. It refires right away but if I dont increase the throttle it will stale again. Could anyone possibly provide me some insight as to something I may have missed or could try? Is there an idle circuit in the fuel system somewhere I am missing?

Thanks for any help you can provide.

Michael,

[99yam40]

did you disassemble the carbs completely and clean in a carb cleaner?
did you remove all of the old gas and clean the tank before adding fresh fuel?

if so might be time to clean with a heated sonic bath cleaner.

did you reset the pilot screws to factory spec and do a link and sync after reinstalling the carbs?

1st thing I always do is check compression check to see if there is a problem with a motor I just came home with

[md544600]

did you disassemble the carbs completely and clean in a carb cleaner?
did you remove all of the old gas and clean the tank before adding fresh fuel?

if so might be time to clean with a heated sonic bath cleaner.

did you reset the pilot screws to factory spec and do a link and sync after reinstalling the carbs?

I did not remove the pilot screws on any of the carbs. I'll have the look up a breakdown for the carburetors. Obviously I missed those unfortunately. Also you seem to be very knowledgeable on this. Could you clarify for me what a link and sync is? Thanks for the help.

[md544600]

Just looked at the schematic. I missed the pilot screws. Looks like I have some more work to do. am i correct in reading remove them, clean them then reinstall to bottomed out and back out 1 and 1/4 turn?

[99yam40]

service manual has a procedures to set all of the linkages properly.
it makes sure all cabs are set exactly the same opening and also the timing.
pilot screws are for the idle mix setting. they have to come out to clean everything properly

it has all of the spec for your motor also

just cleaning the screws is not what needs to be cleaned.
the jets and all passages need it also

[TownsendsFJR1300]

https://www.boats.net/catalog/yamaha...406/carburetor

Pull jets 20 and 23 and check / clean them. If you can't see light thru them, their NOT clean..

[md544600]

https://www.boats.net/catalog/yamaha...406/carburetor

Pull jets 20 and 23 and check / clean them. If you can't see light thru them, their NOT clean..

Yep I got those ones good and clean. I did miss the pilot circuit so I believe 99yam40 has me on the correct track. Thank you for the advice. I have to remove all the carburetors again anyway to check the pilots so I will be rechecking everything again in those as well. Thanks again.

[robert graham]

My C90 very similar to yours was cutting off a idle....I removed each idle mixture screw from top of each carb, remembering the turns out from lightly seated for each one....sprayed carb cleaner in each orrifice then blew it out with an air hose....replaced and set each screw....fixed the problem right away! ....Been running this motor since new in 1999 and only had to do this procedure once....give it a try

[md544600]

My C90 very similar to yours was cutting off a idle....I removed each idle mixture screw from top of each carb, remembering the turns out from lightly seated for each one....sprayed carb cleaner in each orrifice then blew it out with an air hose....replaced and set each screw....fixed the problem right away! ....Been running this motor since new in 1999 and only had to do this procedure once....give it a try

Thanks for the info. I absolutely will be doing this next chance I get to work on it.

[robert graham]

Thanks for the info. I absolutely will be doing this next chance I get to work on it.

Yep, it worked for me....a simple 10 minute job....must have been some trash in one of those passages. Fuel/Water seperater type filter is a great idea here!..

[md544600]

Just thought I'd provide an update on the situation. After removing all the carburetors again and removing the pilot screws cleaning everything again and replacing them, it seemed to be worse than the previous attempt. I wondered what the heck was going on. I drained some fuel and saved it in a clean container and it appears that there is a significant amount of water and contaminants in the fuel. So I decided to to start investing the fuel tank. It's a plastic tank made by skyline industries. As soon as it removed the floor pieces I discovered where I believe the water is coming from. The sending unit and pick up tube gaskets are totally shot. I believe this is allowing water into the tank. What I can't figure out is why the fuel/water separator I installed isn't taking care of this problem. Regardless I have removed the tank and will be removing everything from the tank and doing a thorough cleaning of the tank. I will drain all the fuel from the filters, lines and carburetors before making any further attempts at running it. I'll provide an update once I've completed all that. Just want to say thanks to everyone who has taken the time to provide me some advice on my situation.

[Jason2tpa]

Did you sync carbs after pulling/cleaning pilot jets? How about adjusting the idle screws and idle speed...are these set to spec after reassembling?

[md544600]

Did you sync carbs after pulling/cleaning pilot jets? How about adjusting the idle screws and idle speed...are these set to spec after reassembling?

The idle screws were set back as close as possible to where they came out. Once it's running like I had it running a few weeks ago it's going to the local yamaha dealer to have the idle speed set and the carburetors synchronized. 99yam40 advised me on this as well.