Plz help BF40 dies down at speed

aremazon

Recruit
Joined
May 16, 2017
Messages
1
[h=1]Hello, I am new to trying "online help" but I tried everything I know with no results. The motor idles nice and smooth in and out of gear but when I start to go it runs perfect for about 20 seconds and then starts running really rough, I have learned that I can either turn the key off and on real quick and it runs fine again for about 20 seconds, or bring it back to an idle and go again it will run really smooth for about 20 seconds then start its rough idle again. I have put a spark plug tester to each of the three plugs, at an idle all appear to fire fine, however when rev-ing cylinder #1 continues to fire as it should, cylinder #2 and #3, loses spark after rev-ing for about 20 seconds. again I can turn the key off and on real fast and all cylinders fire as they should for about 20 seconds. I can also bring it back to an idle and rev back up it will work as it should for about 20 seconds. I have tested the oil level, oil pressure sensor, temp sensor, engine temp, timing, timing belt, replaced impeller, inspected for clogs in the water routing. changed spark plugs, changed engine oil, lower unit oil..... there are no warning lights on or buzzer sounding. I have been messing with this and have had no luck for about 6 months, any help would be very much appreciated.[/h]
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Seems an electrical related problem, one electrical or electronic component heats up shorts and misses, worse at more throttle than at idle. Will need to troubleshoot each component by itself. Need a Service Manual and testers to check electrical specs.

Happy Boatingers
 

ahicks

Captain
Joined
Sep 16, 2013
Messages
3,957
Sounds like it's running out of gas to me. It's getting enough to run on idle, but when demand is increased, it can't provide it. Problem could be about anywhere from the tank to the carbs. Tank could have a plugged screen in the pick up, fuel filter could be contaminated with crud or water, fuel pump could have an issue requiring cleaning or rebuilding, or the carbs might have plugged jets.

If it were mine, I'd remove the fuel line from the carbs and try squeezing the primer bulb. If fuel seem to flow freely, it's time to have a look inside the carbs.....
 
Top