2004 90TLRC Rough Idle

I have a 2004 90TLRC that is missing and running rough at idle. Above 1200 RPM it runs perfectly. I've replaced the spark plugs, water separator and run Yamalube oil.

I am suspicious that it may be something to do with the Prime Start System. When I first start the engine, it runs at about 1500 RPM (runs OK) and then slows to the 800-900rpm area after about 30 seconds. Once it slows, it begins missing severely and sometimes stalls. The Prime Start Pump is equipped with a 3 position valve (Normal, Open, and Closed). In normal, it behaves as descibed above. In open, the motor idles perfectly, and in closed, it idles poorly immediately after start-up.

I have the Clymer manual and removed the electrothermal valve and checked the resistance. It was 3 Ohms (in spec). I also removed the 3 screws holding the Prime Start Pump cover in an attempt to remove and clean the assembly, but it would not come off. It seemed like it was being held on by the 3-way valve, but the manual just says to remove the three screws. I didn't want to pry on it fearing I might break something. I have a Florida Keys trip in a week and am counting on having my boat working.

My question's are : Does the Prime Start system sound like the problem? How do I get the Prime Start Pump Cover off?

Any advise is greatly appreciated. Thanks in advance.

i have identical problem mwillia

I also have a 2004 90tlrc. Up until a month ago everything ran perfectly. Then I had the gas tank replaced (fiberglass to some sort of plastics). After this the motor began to have major problems idling. I have experimented with several things:

One is exactly what you are talking about, the prime start pump. At the closed position it won't start, at the normal it has your aforementioned problems, and at open it idles very well for approx one minute then rpms drop to about 500 and it sputters and dies. I am not sure if it is bad to have it to the open setting, but that is the only way i can get the motor started.

I also thought it could be the carb. I have taken that apart and sprayed carb cleaner through all of the valves. It seemed to run a little smoother at first, but the problem still exists. It is possible that I did not clean it thoroughly enough; not sure.

Other minor things are checking the pump bulb, adjusting the idling speed, and changing the fuel filter.

Problem still exists. After doing more research based on other peoples problems and solutions it still seems like a carb related issue. let me know if/how you resolve this issue.

[boats.net]

Probably need to remove and clean carbs, the oring may be swelled up making cover difficult to remove but should come off with a little pressure.
tcc it sounds like the carbs are still plugged up on yours.