84 90hp merc hesitates, won't open up

[pudd50]

It starts easily and runs fine at idle. At half throttle it starts to hesitate and surge. At full throttle it will only run about 4000rpm. I have changed all six plugs and have spark, rebuilt the carbs, replaced the fuel fittings, checked all fuel lines for blockage. The compression is 90psi or more. Fuel pump is clean and looks good but will rebuild it when the parts arrive. I suspect it is a stator problem but don't know how to check it. Any ideas?

 

[Joe_the_boatman]

Re: 84 90hp merc hesitates, won't open up

We need to check both fuel and ignition when the problem occurs. Take the engine cover off, and have someone else drive. At full throttle (4K rpm's) spray premix into the carbs. If RPM's increase, you know you're starving the engine of fuel and you have a fuel problem.

If it bogs down (because it's flooded), you have another problem. Clamp a timing light onto each spark lead and watch for it to drop out or become irregular when at full throttle. If you find a cylinder is dropping out, you have an ignition problem. Start here: http://outboardparts.com/troubleshooting/printguide.htm


The general rule with electric components is to thoroughly test each system, identify the malfunctioning part, then replace. In other words, don't buy anything until you're sure it needs replacing.

 

[pudd50]

Re: 84 90hp merc hesitates, won't open up

Thanks for the tips. I will install the fuel pump rebuild kit this weekend and post if it corrects the problem.