Merc 140 low RPMs

Don S

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: Merc 140 low RPMs

A few more possibilities.<br />Vacuum leak, dirt/water in carb, low fuel pump pressure, plugged screen in fuel pickup tube in tank, plugged or damaged antisiphon valve in tank.<br />Fuel system between tank and fuel pump sucking air from loose or improper clamps on hoses. Dirt/water in fuel filter.<br />To check for air getting into system, plumb a short piece of clear hose from fuel pump to hose and run engine. If you see bubbles, you have an air leak. A common cause of air leaks is using the 1/2" wide hose clamps on small fuel lines, it leaves a flat spot under the screw and allows air in. Using the small 1/4" wide mini hose clamps prevents that problem.
 
J

jenny1671

Cadet
Joined
Jul 31, 2004
Messages
27
Re: Merc 140 low RPMs

My 19.6" Doral has 140 hp. top speed attained 29mph.<br />The boat has been tuned up last week. It has a new Prop. We changed spark plugs, points, ignition coil, new starter, new battery cables, changed gear and engine oil, new cap and rotor, and condenser. Relocated fuse panel, all fuses checked are a ok. Checked carborator its tight.<br /><br />I still have max rpm at 2900. It idles at 650 to 700 rpm on Start up and Water temperature is at 140. oil psi is good. Cuts out when increasing spead from idle to quarter speed. Its Ok when spead is increased slowly but has a ping at half throttle. Then ping disappears at three quarters to w.o.t. <br /><br />Things to be done is change feul filters. <br />Could it be the accelerator pump causing it to bog and loose RPM? Or Would a dirty fuel filter cause it to loose rpms?
 
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