Yamaha 40 4 Stroke problem

I have a 2001 Yamaha 4 Stroke 40hp. I have had absolutly no trouble out of this motor until now. The problem is that it will start and run fine until put under a load in the water. When I put it in gear and try to throttle up it wants to cut out and try to die. I have since taken it to my mechanic (who has been working on outboards of thirty years) and he has run every test under the sun, and finally we have come to the conclusion that one of the caburators is not working properly. He cleaned it and the problem got better but still not enough power to plane the boat. He then contacted Yamaha and there answer was to replace the carb cuz that model there are ports in it that just cant be reached to clean, and that they had so much trouble with that design that they later discontinued it and went to fuel injection. My question is has anyone else had this problem and what did you do. I personally have never heard of carbs that cant be cleaned and rebuilt at least once.

40 HP 4 Stroke Carb

Yep, looks like I have the same issue even though my mechanic did not have the right adapter to check the compression. Assuming that comes back positive looks like new carbs.

Yep, looks like I have the same issue even though my mechanic did not have the right adapter to check the compression. Assuming that comes back positive looks like new carbs.

Pete

my mechanic has performed every test ( electrical and fuel ) that can be done, and it all leads back to the one bad carb. I have done extensive research online on this problem all feedback says replace carb. Yesterday I talked to a friend that used to be a yamaha rep and he told me to contact yamaha customer relations and explain the problem and they possibly would send me a free carb. I will let you know what happens.

Yep, looks like I have the same issue even though my mechanic did not have the right adapter to check the compression. Assuming that comes back positive looks like new carbs.

Pete.........I have one other solution you could try I did and it worked for me.....First combine one quart Seafoam with three quarts gas and put into clean empty tank. Second run your motor on this mixture until you see some improvement. I tried this as recommended by a friend and after the second gallon of the mixture was about half gone i took the boat to the lake. Put the boat in and it started off sluggish wanting to die, but after a while it lined out and it is running better than it has in a long time. Forty dollars worth of Seafoam just saved me almost $500.00.....Thanks Seafoam!!!!!!

I have a 2005 40hp 4 stroke also. Same problem. Bought it new 2 yrs ago. I ran great the first year. The dealer winterized it. I changed the plugs the following spring and a couple more times since then. Ran seafoam through it for a couple tanks. No real improvement. I started simple this spring with new plugs again and installed new hose clamps on the external fuel line from the tank to the engine as a precaution. I drain my tank empty every fall so there's no worries about old fuel problems. I guess I'm not alone with this issue. Last year, everytime I'd go to throttle up, it would start chugging and almost die. I'd have to quickly let off the throttle then nail it again and it would clear up and plane out. Seems to be better so far this season.

[Ritchiel]

2002 40hp

I had the same problem. I took it to my mechanic he had to remove the carbs and soak them after he put them back on the engine ran like a new one. he said I should drain the gas from the carbs and not to use any gas that has ethanol in it.

[Ritchiel]

Winter

My mechanic also said in the fall I should drain the carbs. But everything I have read so far no one has done that. he said remove the screws on the bottom of the carbs. Any one do this??????????

[robert graham]

Just a thought, but I've heard of folks using an ultrasonic cleaning bath for carbs since the jet passages are so small. Regarding draining the float chambers, I do drain mine about twice a year and especially at winter shut-down. Use the Stabil all the time and install a fuel/water seperater type cartridge filter(Walmart/Attwood $27), easy 2 screw installation, save yourself all this dirty fuel/carb grief! Good Luck!

[DoWhatsBest]

40 hp carb problem

I read on another blog page that a guy changed his carb jets from the standard f40 jet which is a number 40 to a F25LA jet and the problem went away.

[boscoe99]

I read on another blog page that a guy changed his carb jets from the standard f40 jet which is a number 40 to a F25LA jet and the problem went away.

Richiel says that he has a 40 Yamaha. Which is a two stroke model.

The carburetor mod wherein bigger jets are used applies to a four stroke F40 model.

And by the way, you are replying to a four year old post.

[Russrob55]

I have similar problem engine bugs down , stop it and start again , runs fine for a little , then bigs down ,and warning light comes on, then goes off.