Logo

2006 40hp 4 stroke won't stay running

teepster

New member
My neighbor has a 2006 40hp 4 stroke yamaha with very low hrs. It would not stay running this spring and he took it back to the marina were it gets serviced and they said the gas in the in-board tank was gunked up. They installed a filter and water separater and he brought it back and put it in the lake and it ran for a few minutes but started to run poorly again. The marina said it probably has water in the carbs which is a problem with these and the carbs would need to be worked on. It would start up and run for a short while for him then quits. I took the cover off looking for carb bowls (3 cylinder) that might be easily drained to remove water but didn't see anything. While I was there it turned over OK and would almost start but never did. We pumped the gas bulb and tried chocking with the key but nothing helped.
1) Is there someway to drain the carbs on these. These 3 carbs are on the side and stacked pretty tight and I didn't see anything that looked like a carb bowl underneath.
2) I thought about pulling the spark plugs for an inspection and trying to start with starting fluid to clean out the lines but the motor did run for a few minutes at slow speeds when it came back from the marina so I don't know if that experiment would work.
any suggstions?
 
Four stroke engines don't like dirty fuel. If you can find the carbs then there are drains for them. I suggest you to find the drain screws and drain all the carbs. Also look for the fuel filter attached to the engine and drain it as well. Then get a small gas tank put fresh fuel in it and hook it up to the motor. Fill up the carbs with fresh gas and run it that way. If it runs good then it's time to suck out all the gas/water from the tank under the boat. The best way to do this is to get an older car's fuel pump. Hook it up to the line to the tank and let it suck it out and dump it into a clear container. You will be able to see water collected at the bottom. When it's empty try to put in 2 fresh gallons of fuel and pump it out again. Try that several times until you see no signs of water. I have done this to my fuel tank recently and it's a PITA but it solved all my running issues. GL
 
Can anyone describe what a carb drain screw might look like on these newer yamaha's. I'm use to seeing a bowl at the bottom of the carb and they somtimes have a drain at the bottom or remove the whole bowl like a lawn mower. These 3 carbs were stacked right on top or each other and I didn't see much space between them so I suspect there may be just a screw that when removed will drain them. I didn't get a good look since I was hanging over the back of the boat while it was in the water but next time I'll get in the water and look at it more closely. I've newer seen carbs on the side of the engine before but I've always owned 2 strokes. Good idea about hooking up a portable tank with fresh gas. We can try my 40hp yamaha tank but clearing the carbs should be done first.
 
Cleaning these carbs is not something you want to start if you aren't familiar with the process. I would find someone with an ultrasonic cleaner and the experience.
 
Just want to get the water out of the carbs. That's what I meant when I said clearing the carbs. Your right, we're not going to work on the carbs past the point of getting the water out if that's a easy enough task.
 
I'm sure you have figured this out by now. Brass screws, stbd lower side of float bowl, slighty forward. They are drilled so you don't need to unscrew more than a couple-three turns. Fragile, don't over tighten. Tip the motor about 20 degrees and turn to stb a bit to maximize drainage.
Pump the primer unil water is gone. Might help to add some dryer. Yamaha fuel conditioner.
 
Back
Top