1978 M-500 low WOT RPM

[dantesilvio]

My 21' Cruiser has twin 50 hp 1978 M-500's with thunderbolt ignition. The engines are identical including same fuel source and props, and both are in great condition. <br /><br />However my Port Engine has a WOT RPM of 4800, while the Starboard Engine has a WOT RPM of 5400. Its my understanding that both engines should have a WOT RPM of 5500. They both start, idle, accelerate and run great.<br /><br />How Do I increase the WOT RPM of the Port Engine?<br /><br />Thanks

 

[tmcalavy]

Re: 1978 M-500 low WOT RPM

Make sure the props are identical before you start monkeying with an otherwise matched pair. Could be someone replaced prop on port engine and put one with a higher pitch on my mistake.

 

[dantesilvio]

Re: 1978 M-500 low WOT RPM

Tim MC<br /><br />Thank you for the reply, but unfortunatly the props on this pair of m 500's are identical.<br /><br />I'm stumped and can not throw a bunch of money at a problem that I'm unsure of.

 

[andrewkafp]

Re: 1978 M-500 low WOT RPM

Throttle/cable adjusted the same ? Maybe one is out of adjustment.<br />What I mean is.. when both controllers are fully forward, are both throttles fully open ?

 

[The Marine Doctor]

Re: 1978 M-500 low WOT RPM

Lets check the compression of both engines. I you do not have similiar compression you will not have similiar performance.<br /><br />Check fuel pump pressure as well.<br /><br />Look for fuel leaking from the carbs as well.<br /><br />TMD

 

[dantesilvio]

Re: 1978 M-500 low WOT RPM

Unicorn and TMD<br />Thanks for the help. I checked the linkages of throttle cable to the Carborators and its wide open. Both engines look to have been set up the same.<br /><br />TMD I will get back to you about fuel and compression.

 

[The Marine Doctor]

Re: 1978 M-500 low WOT RPM

I will be here waiting.<br /><br />TMD