No power under load Yamaha F40 outboard 4 stroke

A 2002 Yamaha F40 hp outboard has no power under load or even when just "goosing" the throttle in neutral. It happened like someone flipped a switch. Plenty of fresh fuel, fuel pressure and volume are fine. I hate to say I did this, but if you give it a shot of starting fluid while accelerating, it will then accelerate as it should. This leads me to believe we are not getting the fuel I should at that point.

Spark plugs are new, spark is very strong on all three cylinders.

What do you think?

Re: No power under load Yamaha F40 outboard 4 stroke

I would say you are correct on not getting enough fuel something is plugging up

Re: No power under load Yamaha F40 outboard 4 stroke

I have th same motor and was having the same problem. I cleaned and cleaned and cleaned the carbs. And it got better but not good. I'll tell you what it most likely is. Your accel pumps in your carbs. You will have to remove and clean them with carb dip. Do not waste your time with the canned stuff. Soak each carb for three hours. Remove as much rubber and plastic as possible. Take lots of pictures as you go. After you get the clean put the spring loaded plunger(about the size of a nickel) back in the bowl and fill the bowl with penetrating oil. And depress the plunger quickly and forcefully untill olenty of oil is flowing with each compression. Set the top part of the carb back on the bowl and depress the throttle lever over and over again untill you are getting a steady stream of oil through the brass tube it will be shooting a steady stream out I the back of the carb. Reassemble and you should be good to go.

Re: No power under load Yamaha F40 outboard 4 stroke

I did have the carbs apart and I did clean them with the canned stuff, Berryman's. It runs a little better, but not great. It sure seemed like the accelerator pumps were working okay, but maybe not. I do wonder if the solenoid on the top carburetor is for more than just cold start enrichment. Does anyone know how the solenoid and plunger are supposed to work? If I put 12 volts to it, it does nothing. Both wires going to it are the same, yellow with a black tracer stripe. When the engine is running it gets warm even though the key is not pushed in for the "choke". I'm wondering if it has anything to do with acceleration enrichment as well as cold start enrichment. Apparently this solenoid on the top carburetor is called the "prime start assembly". Since it does nothing when I put 12.6 volts to it, I'm very tempted to replace it, but it is a $253.00 part. I cannot find any info on it with various internet searches.
When I cleaned the carburetors they really did not appear to need it, but I did it anyway and it does seem a bit better.
Thank you for the suggestions so far. I would really like to know more about the prime start assembly.

Re: No power under load Yamaha F40 outboard 4 stroke

the manual is a lot cleaper than that part you are guessing at. the solinoid is the choke it closes the choke plate on the carbs. there should be power and ground at those 2 wires,1 12 volts and the other should be ground when key is pushed in. if it feels hot then its becauses its getting power and closeing choke valve ,adding more fuel in this situation would cause it to bog more or even die. adding fuel/starting fluid makes me think you aren't getting enough fuel. if choke is stuck the plugs will be black and sooty.

Re: No power under load Yamaha F40 outboard 4 stroke

V-Tech said:

I did have the carbs apart and I did clean them with the canned stuff, Berryman's. It runs a little better, but not great. It sure seemed like the accelerator pumps were working okay, but maybe not. I do wonder if the solenoid on the top carburetor is for more than just cold start enrichment. Does anyone know how the solenoid and plunger are supposed to work? If I put 12 volts to it, it does nothing. Both wires going to it are the same, yellow with a black tracer stripe. When the engine is running it gets warm even though the key is not pushed in for the "choke". I'm wondering if it has anything to do with acceleration enrichment as well as cold start enrichment. Apparently this solenoid on the top carburetor is called the "prime start assembly". Since it does nothing when I put 12.6 volts to it, I'm very tempted to replace it, but it is a $253.00 part. I cannot find any info on it with various internet searches.
When I cleaned the carburetors they really did not appear to need it, but I did it anyway and it does seem a bit better.
Thank you for the suggestions so far. I would really like to know more about the prime start assembly.

Click to expand...

This should help you understand the prime start system
http://forums.iboats.com/showthread.php?t=357552

From what I have read the F40 is a hard one to get the carbs cleaned and adjusted properly, and you will need the proper equipment/tools to get them cleaned and adjusted so you would be better off taking it to a good Yamaha service shop and have it done. The canned cleaner will not get all of the small passages cleaned out

Re: No power under load Yamaha F40 outboard 4 stroke

Thank you very much for everyone's input. I read the thread link you provided and it was very helpful and informational. I will try cleaning the carburetors properly....again.

I will follow up with the outcome.

Re: No power under load Yamaha F40 outboard 4 stroke

well you get her going??