BF40A dies at throttle up

[tcurtis]

I have a 1996 BF40A. Has been a great motor. No problems other than general maintenance. Probably has close to 2500 hours on it. New plugs every year. Starts immediately. Wans to die on throttle up the first 5 or 6 tries. Once it goes - it will run great the rest of the day. Repeats this scenario every time I put it in the water.

 

[hondadude]

Maybe your thermostat is not letting the engine getting up to temperature quickly. Check to see if it is stuck open.

It could be a carburetor issue, but not very likely, since it runs ok after a while of running.

Mike

 

[bobmech]

I have experienced the same problem and it also only occurred when the motor was cold e.g. stalling on the first attempts to throttle-up after starting the motor from cold.
In my case it was caused by slightly stale low octane fuel combined with cold ambient temperature of about 10 deg C.
Here is a thread from someone with the same problem.
http://www.marineengine.com/boat-forum/showthread.php?214624-Honda-50hp&highlight=lean+cruise

Bob

 

[hondadude]

Very interesting, bobmech. That does make sense.

My rationale for suggesting the thermostat rather than anything else, was something that he did not say...

He did not say that it has been that way for over 2500 hours.

Unless he is doing something different, like using different fuel or operating in different ambient temperatures or altitudes, I picked something simple.

Could also be spark plugs are slightly fouled by carbs idling too rich as he idles in to the dock, thus the plugs do not work efficiently until they are "cleaned" by higher speed operation.

The engine may just need a good decarbonation.

It might be wise to perform a compression test to see if there is an issue that way.

I guess, the more I type, the more thoughts I have.

Mike

 

[tcurtis]

Thanks for the suggestion about the thermostat. I will check into it. It is the original thermostat and has never been replaced. Since the day I bought the motor I have always ran 91 octane fuel. I also use sea foam in the fuel and run 1/2 can of Mercury Power Tune through the motor each Spring. I do a lot of trolling. I have never replaced the fuel filter as well. The last time it was checked it was fine. I am not a mechanic by any means but have learned to do most work myself as the closest Honda dealer for service is 200 miles away. Last year - my shift cable broke and I replaced both the shift and throttle cables at the same time - myself. The problem has gotten worse since I replaced the cables. The motor runs fine in he driveway at home. But under a load it wants to die at about half throttle. If I can keep it running past half throttle it takes off and runs great after that. It is just getting it running that it time.