150 Mercury Blackmax- High Speed Problem

[screamindrag]

My 1989 Mercury Blackmax XR4 just learned a new trick. It cranks fine, idles fine and gets up on plane with no problem. Once I get up on full plane and start running full speed, for about 10 seconds, the motor acts like it runs out of fuel and idles down. After the motor slows down, I can get back up to full speed again within a few seconds and the same thing happens. The motor just started doing this all of a sudden. I replaced the fuel pump, rebuilt the carb, replaced the primer bulb and fuel lines about 6 months ago. I am new to working on my outboard motor so I am not really sure where to start to diagnose the problem. Any suggestions on where I should start? I was thinking I should change the primer bulb and fuel lines again as well as clean the carburetor with some carb cleaner. Any advice will be greatly appreciated. - Thanks - James T.

 

[aussieflash]

Re: 150 Mercury Blackmax- High Speed Problem

Could be a lot of things but those symptoms point toward a bad Stator.I would be checking that first.Good Luck.

 

[Chris1956]

Re: 150 Mercury Blackmax- High Speed Problem

Does the primer bulb collapse? If so you have a restriction in the fuel line, likely the antisiphon valve, fuel tank vent or a filter. I do not think there is enough evidence to suggest the stator is bad.

 

[Colelj]

Re: 150 Mercury Blackmax- High Speed Problem

I had this same problem last year on my Johnson and it was the clip that plugs into the front of the motor that your fuel line is attached to. It was full of rubber from the inside of old fuel line coming apart. I cleaned it out and was good as new. Hope this helps.

 

[screamindrag]

Re: 150 Mercury Blackmax- High Speed Problem

Thanks for the suggestions guys. I replaced the fuel line all the way from the gas tank to the motor including the primer bulb a few months ago, motor hasn't had 10 hours on it since then. This is not to say that I don't have trash in the fuel line again. The primer bulb does not seem to be collapsing but I am going to replace the fuel line and bulb again, just to be safe. Could this problem be caused by water or bad gas? Could the high speed jets in my carb be stopped up? If so, should I go ahead and spray some carb cleaner? Could this be the fuel pump acting up at high speeds only? Any more suggestions? I want to do everything I can to fix this problem before my tournament this weekend. I will not be able to go to the lake and test the motor before the tournament because the closest lake to me is an hour away so the next time I run the boat will be for the tournament this weekend. Thanks again!

 

[Chris1956]

Re: 150 Mercury Blackmax- High Speed Problem

Pump the primer bulb and see if the issue goes away. If so, you may have a weak fuel pump or air leak in the fuel line.