Outboard ran fine but now won't idle without stalling

[KenG]

Can anybody identify what's wrong with my motor?

I have a 40 hp Yamaha 2-stroke with remote controls. I was out on the lake yesterday and had just finished a 15 minute run at full throttle, everything seemed OK. I slowed down to idle to make a turn, then when I applied throttle again the motor died. I couldn't get it to stay running. It started fine, but ran rough and cut out after 5 - 10 seconds. I limped to a nearby dock using the trolling motor, tied up, and checked that I had gas (I did). I checked the fuel filter visually (it looked OK). I replaced the three spark plugs with spares I carry on board. By fiddling around, I found that I could stay running at slightly above idle, but I don't think the new plugs were the reason. At idle it would stall, and at about half throttle position it would stall. I ran at low speed back to the dock where I had launched. On the way, the motor rpm at one point jumped up without me moving the throttle and I was able to move the throttle to 2/3 and run back to the home dock. As I approached the dock I dropped into idle and the motor cut out. I called my wife who brought me carb cleaner, tried it, but it did not help. It was back to running for 5 - 10 seconds and then cutting out, even at idle.

I will most likely take it to the repair shop, but would rather fix it myself if I can. It sounded to me like a dirty carb or plugged fuel filter so I'll start there.

Does anybody recognize these symptoms?

BTW, the boat is a 2000 G3 175 pro mv.

 

[Natedog57]

Tech Sergeant Ken » 21 Jul 2014, 06:56[/url]"]By fiddling around, I found that I could stay running at slightly above idle, but I don't think the new plugs were the reason. At idle it would stall, and at about half throttle position it would stall.

On the way, the motor rpm at one point jumped up without me moving the throttle and I was able to move the throttle to 2/3 and run back to the home dock.

Everything you've said here represents classic symptoms of clogged/dirty carb(s).

Spraying carb cleaner into the carb throat probably isn't going to do anything but lean out the fuel/oil mixture, and excessive amounts will cause ring failure.

You'll need to pull the carbs, dissemble, clean. I use aerosol brake cleaner to shoot into all the tiny passages. It's up to you to do a total carb rebuild, or just cleaning. If it was running great previously I'd probably just clean things and see if that works.

You need to be careful to record the position of the idle set screw (1 on each carb), either screw in tight counting turns, then remove, or leave alone entirely. I'd probably leave the screw alone, but dissemble everything else.

Lastly, there is a reason it started running poorly, maybe bad/dirty gas... I've had the fuel lines (under the cowling) degrade because of age/ethanol and the tiny pieces clogged the carb. Whatever the reason, you'll need to fix the cause of the issue or good chance it will happen again.

 

[KenG]

Thanks for the helpful response. I did take it to a marine mechanic who confirmed that it is a carb issue. He also mentioned that I need new fuel line and primer bulb due to "new ethanol" issues. Not sure what that means but will probably get that done , too.

 

[Kismet]

Tech Sergeant Ken » Today, 12:43[/url]"]Thanks for the helpful response. I did take it to a marine mechanic who confirmed that it is a carb issue. He also mentioned that I need new fuel line and primer bulb due to "new ethanol" issues. Not sure what that means but will probably get that done , too.

New ethanol added gasoline is corrosive to old rubber hoses. Look around for a station that sells Regular gas, with no alcohol added. Costs a few cents more, but I get it for outboards and lawn mower.

Also, you might check around for a funnel that screens out water in the gas. I got mine at Amazon (I think) and it is a small precaution to take, and cheap. Stored gas...in underground tanks or in boat motor tanks can develop some condensation and mess with the quality of the engine's efficiency.