1996 johnson 100

I recently purchased a 18' Wellcraft with a 100HP Johnson. The motor runs good at the first part of the day. Shortly after running for a while it seem to hit 3000 rpm at full throttle. I've gone through the fuel pump, lines, and replaced filters. Checked for air leaks. Any suggestions as to what else could be the problem. Thanks

Re: 1996 johnson 100

Sounds like gummed-up high speed jets from old/bad fuel. Before you tear into the carburetors, take it back out to the river, lake, whatever and, after warm-up, push the throttle up to WOT. Note the RPM's and then push the choke button on your remote control. If it is the high-speed jets preventing higher RPM's, the motor should respond to the extra gas being injected into the carbs. May not reach normal WOT RPM's rated for your motor, but should briefly catch on and run smoothly up to 4000-4500 RPM's for a few seconds. If this does NOT work, then your problem is somewhere else in your fuel supply system eventhough you have already made one pass through it. I just had what sounds like the same problem with a 2004 Mercury 60HP and had to clean out the jets. Good luck and let us know what happens. Lots of very experienced and helpful people on the forum.