OMC 305gm STILL will not go over 2500 rpms!

[kicks2]

Here is an update, which includes everyone's feedback!<br /><br />Replaced the coil, pts, plunges, condenser, cap, rotor, H20 separator, fuel filter and siphon valve.<br /><br />Checked timing to verify it is advancing, checked all fuel lines for blockage, checked cylinder compression (all of right bank at 150psi, all of left bank at 170psi) checked carb & choke linkage for binding, checked cut out switch for correct operation and rebuilt the carb.<br /><br />And it still will not go over 2500 rpms!<br /><br />The fuel pressure at the carb is 3.5 psi, the manual indicates it should be 5.75 to 7 psi. But, spoke to 2 marinas and they both stated that it is not the fuel. Fuel pumps either work or quit!<br /><br />I am dazed and confused. Can anyone help!?<br /><br />Your input would be appreciated. Thanks Joe

 

[Bondo]

Re: OMC 305gm STILL will not go over 2500 rpms!

Replace the Fuel Pump.......<br />If that Doesn't do it.....<br />Go to a Smaller Prop......

 

[loadnet]

Re: OMC 305gm STILL will not go over 2500 rpms!

I second the motion of Bondo..<br /><br />The fuel pump is supposed to supply more fuel pressure than what you have stipulated.<br /><br />If your boat ran above 4000 RPM with the current prop prior to this low RPM problem errupting then FOR SURE change the fuel pump - point blank.<br /><br />If your boat has NEVER ran higher than 3000 RPM, find a dealer that will allow you to test downsized props till you get the correct one enabling you to run up over 4000 rpm.<br /><br />PB

 

[rodbolt]

Re: OMC 305gm STILL will not go over 2500 rpms!

hello<br /> I cannot find where you are sure the boat ever ran more rpm.<br /> I use an IDC dyno to test power output. that tells me whether is engine or prop related. and depending on the year if S.L.O.W. kicks in it will limit you to 2500 rpm.<br /> keep us posted

 

[kicks2]

Re: OMC 305gm STILL will not go over 2500 rpms!

What is S.L.O.W.?

 

[rodbolt]

Re: OMC 305gm STILL will not go over 2500 rpms!

hello<br /> S.L.O.W.<br /> stands for speed limiting overheat warning . it was and still is used on some outboards and I/O's. it limits the RPM or reduces it to aprox 2500 rpm. good luck and post more info

 

[kicks2]

Re: OMC 305gm STILL will not go over 2500 rpms!

Thanks, do you know where it is located? By the way, the boat has ran very well and could obtain 4500 rpms. This problem now happens with or without a load. <br /><br />Thanks for you input, please keep it coming.<br /><br />Joe

 

[jimmmy]

Re: OMC 305gm STILL will not go over 2500 rpms!

I too have a similar problem on a new used boat I bought this year. Can't get over 2900RPM under load. Used to be 2400RPM but have changed to 17 pitch prop to get RPMs up. Had two seperate marine mechanics look at it ($1600) and still no better. I'm able to get 4500RPM in neutral but not under load. Changed wires, distributor cap, rotor, condensor, coil, carb rebuilt, head gasket and head machined due to warping. Hope you find a solution so I might find one.

 

[bomar76]

Re: OMC 305gm STILL will not go over 2500 rpms!

It's a power loss problem, not enough HP under load.<br /><br />Fuel starvation? That pressure reading (if accurate) is TOO LOW.Put a new pump on it.<br /><br />Intake leak? (manifolds or carb-spray carb cleaner around manifold and carb base while running to check-you'll know if if sucks in)<br /><br />Flapper stuck shut? (This would give a tremendous exhaust restriction and act like a plugged cat on a car-low power)<br /><br />Compression? (What is it?)

 

[kicks2]

Re: OMC 305gm STILL will not go over 2500 rpms!

compresion is 150 psi on left bank & 170psi 0n right bank. What and where is the flaffer located on a OMC with a gm 305 - 1988. Thanks for your input. Joe

 

[bomar76]

Re: OMC 305gm STILL will not go over 2500 rpms!

Before you do anything else, put a fuel pump on it.<br /><br />I have no idea what you mean by "compresion is 150 psi on left bank & 170psi 0n right bank." <br />What is the compression of each cylinder? They should vary no more than 10%.<br /><br />Again, put a fuel pump on it before you do anything else....that's too low.<br /><br />The flappers keep water from flowing back into the manifold and engine. They will be in the risers on top the exhaust manifolds.<br /><br />Put a new fuel pump on it before you do anything else. Then do the carb cleaner spray bit to look for a leak.<br /><br />Did I mention the fuel pump thing?