Motor is 1990 175 on a 1973 Mako 20. Picked up this motor in the spring and mounted on my project. As preventative maint. rebuilt water pump, fuel pump, poppit and thermostats, and tore down and cleaned carbs. Installed Merc water/fuel separator. Oil injection is removed and blocked off as per this forum. Thanks John, great info on how to do that. All was running great; idle, off idle, WOT running about 5100 ;39 mph. I am using above deck tanks since I do not trust the below deck 38 year old tank. Well, in the process of filling tanks, I forgot to open the vent on the tank that was hooked up to the motor. Swelled up like a ballon, probably for an hour or so. Now when I run, idle is perfect, 650 to 750, but as soon as I give it a little throttle, rpms jump up to about 1300. Did no tsee any fuel leaking out of the carbs. Engine does tend to miss and sputter at off idle. I can slowly back down on it, but usually just drops back to idle. I did find a lot of crud in the filter from above deck tank (not related to the expansion, just running around prior to my screw-up). I guess I didn't clean it out very good. Changed filter, installed a new "on engine" glass sight filter. The one on there was old, but after opening it up, did not find any trash. I have adjusted the throttle cable as per the manual, but still the same "off idle" jump. It is not surging as I have read about on this forum, just cant get it to slowly increase in rpms. I am thinking fuel pump may have damage due to the pressure build up. But, anything after about 1500, she runs great. Planing on pulling pump and the carbs and cleaning again. Next suspect would be the "off idle" jet. Note: did the seafoam treatment yesterday. Smoothed out the idle a little, but still have the "rpm jump". Neighbors thought I was expermimenting with a new "outboard mosquito repellant."
Any thoughts on this would be appreciated.
Any thoughts on this would be appreciated.
