Merc 500 timing & rpm

[cbcrawford]

OK, <br />'73 merc 500 50HP, want to set the timing, but the little RPM thingee on the controls is burnt out. <br /><br />question - is there a way to read the engine's RPM's another way? I'm very handy, but very inexperienced at this!<br /><br />The problem I am having is getting up on plane with any load greater than just me (embarrased the other day trying to take a buddy fishin w/me).<br />Before I go and change out the pitch on the prop I want to make sure that the motor is healthy and find where it is in the RPM range. I do have a shop manual) Recently had a shop change out the plugs and clean out the carbs, I had the impeller & water pump replaced, and changed the lower unit oil. There is still the occasional chug. I am assuming the timing is the next logical step, then based on the RPM's I can consider going to a lower pitched prop? (current prop is 14, I can get a comprop at either 13 or 11).<br /><br />Thanx in advance for any help!!!<br /><br />CC

 

[Ben Konopacky]

Re: Merc 500 timing & rpm

sho boat, You need a good Tach.to do anything in a right manor.Otherwise you are only guessing ,and you should get a service manual for that motor to set up the timing.do this before swopping props.

 

[cbcrawford]

Re: Merc 500 timing & rpm

Thanks for replying.<br /><br />The problem is this - the rpm (or tachometer) hookup in the control unit is fried, so the question I was posing is, how do I get the RPM's, or how do I hook up a tachometer to this engine somewhere not on the control box?<br /><br />I do have the manual, but unless I can get a tach hooked up or get the RPMs another way I have to replace the controls . . . something I would, for obvious reasons, rather avoid.<br /><br />CC

 

[Ben Konopacky]

Re: Merc 500 timing & rpm

sho boat; new tach. gets wired from control box. black to -neg.,white to +pos.,brown to signal on the tach. hope this helps.

 

[cbcrawford]

Re: Merc 500 timing & rpm

OK, thanks again for the help, and not to sound ungrateful, but PLEASE read my question this time before responding.<br /><br />The Wire in the control unit is Fried. No Good. Won't work. dead. (see both posts from me above). I can't hook it up there, the grey wire is burnt, and there is no anything coming from it.<br /><br />The question is this - Is there somewhere else I can hook up the tachometer that will give me RPM's on this motor without replacing the controls? <br /><br />PS - text conversations like this don't let folks use voice inflection, so if this reads as smart-alec, whiney, or rude, please don't take it as such, I really just want to make sure that the question that I'm asking is the one I'm getting an answer to.<br /><br />CC

 

[bh357]

Re: Merc 500 timing & rpm

The "Send" terminal on the tach should hook up to either of the yellow wires on the rectifier. At least that's the way it worked on my 1963 inline 6.

 

[cbcrawford]

Re: Merc 500 timing & rpm

THANKS -<br /><br />worked like a charm.<br /><br />(and thanx for answering the right question!)<br /><br />CC<br /><br />PS - now for the compression test . . .

 

[Ben Konopacky]

Re: Merc 500 timing & rpm

Sho-Boat; I guess having a manual realy does not make a bit of a differance !! "IF YOU DON'T USE IT " It does have a schematic (picture)of the wiring,all you had to do is "LOOK". sorry