Black max 150 problem....

[saltfisher]

I been having some issues with this motor backing off on me at full throttle. It was fine the past 2 times out, and then I replaced the primer bulb (found a small leak), and spark plugs and it started doing it again.

One thing I dont get, is I launched the boat, and ran the motor for about 5 minutes. Its a 1988 black max 150. Figured this was enough warmup time, as it was a warm night. Maybe 70 degrees. I go WOT and the motor RPM went up just a little bit and we were only doing about 20mph at WOT. Then it felt like it was trying to pick itself back up, stuttered a little.... then I backed off to not hurt anything. Then tried again, and it still did it, and while i was at WOT going this slow speed all of a sudden it kicked in, and we were doing about 40mph. Then it wouldnt go faster then this for about another minute. Then it had another "kick" and then it was fine at we were topping 60mph. It also wouldnt stay running at idle. Everytime i would go to idle speed or a very slow forward speed it would slowly bog down and die off. It would start right up if i lift the fast idle speed lever maybe after a few cranks. Also i noticed that when i start the engine cold it sort of "spits" or "coughs" a few times. Sounds like a very loud sneeze. Maybe does this 4-5 times in the 1st 30 seconds of starting it then it stops. Maybe this has something to do with my problem? I dont know why it was fine the 2 times out before this though. It would idle fine, run great and not back off on me. Now this new problem comes around and figure maybe you guys can put 2 and 2 together and maybe come up with some ideas.

Thanks

 

[j_martin]

Re: Black max 150 problem....

The power drop is probably ignition miss. You must have a couple of cylinders dropping out, and picking up seperately. Sometimes it's hard to find unless you set a trap, such as puting a timing light on one plug at a time to see which is misfiring. If it's really acting up, and you make about a one minute loop back to the dock and shut down, the really wet spark plugs would be the mis-firing cylinders.

I am assuming that you have already checked into water in the fuel, pinched fuel lines, and all that stuff.

These motors will sneeze when they are running lean. In colder weather, I have to lay on the choke switch for about 20 seconds after it starts. The sneeze could be hard on the reeds, but otherwise is harmless. It's known as the "lean sneeze"


hope it helps
John