50 HP Yamaha, rough idle

My 2003 50HP Yamaha has had the carbs rebuilt and the engine tuned up in May. After about 20 hours run time, the idle is rough, and it slowly degrades until the engine shuts down. I checked the "new" plugs and they are black and wet. It also appears the oil level is increasing (gas?). No water separates out of the oil. Any ideas?

Re: 50 HP Yamaha, rough idle

Its a 4 stroke ?

Re: 50 HP Yamaha, rough idle

Wet, black plugs would indicate that the mixture is too rich. Excess fuel could also increase the amount of unburned fuel in the oil. Check compression and if that is OK (would indicate bad rings) it is probably the carb(s). Could be as simple as some dirt stuck in the float. You don't indicate that the engine is missing, but a mis-firing plug could also lead to wet plugs, but they are usually not black. The black plug indicates incomplete combustion.

Re: 50 HP Yamaha, rough idle

Yep, it's a 4-stroke.

Re: 2003 50 HP Yamaha 4-stroke rough running

Re: 2003 50 HP Yamaha 4-stroke rough running

The rough idle is fixed with a new fuel pump. Now I have missing and rough running at 1500 to 2500 RPM. Will this never end??? Has anyone else had a rough running engine with good compression, good leak down, new carbs, new fuel, profession link and sync twice, new filters, etc.??? I need some help. I'm going to have to mortgage the house to pay for repairing a 50 HP, 4-stroke, "High Quality" Yamaha motor! The few fish I have caught this year on the limited time the boat has been able to be in the water has cost me about $600/pound.

Re: 50 HP Yamaha, rough idle

Where are you having the motor repaired? Is it a Yamaha dealer? Do the mechanics have a Master technician rating?

Re: 50 HP Yamaha, rough idle

I won't give the name of the Marina because they are doing their best working with what they have to work with. And, yes, there are two Yamaha certified Master Mechanics on board. Any more certificates, and thay would need a new wall.

Re: 50 HP Yamaha, rough idle

you may need to check for airleaks/restrictions from the fuel pump back t the tank, try a spare tank to discount problem with your main tank ( your tech would not have checked these for sure);

If you have a timing light mrk the TDC mark on the flyheel, check that timing pointer is set at TDC, mark TDC mark on flywheel with whiteout and run the motor, and check timing marks it should be 1.5 degrees +/-i. if not check you ignition system for propblems;

if a new in-board water separator is used and was replaced, check that it is firmly screwed in; the 4 stroke timing is managed by the ignition module, this seems to be fine as the motor fires up and idles well; link & sinc requires a vacuum gauge or manometer to check and set sinc; what you are describing leads me to think that your carbs are out of sinc, the dash-pot may need adjustment as well;