Adjusting idle & throttle cables, 1975 Mercury 500

Sidhewynder

Cadet
Joined
Dec 15, 2010
Messages
17
Hi Everyone,

I have a Mercury 500 Serial #4286099 (1975?) that I'm trying to breathe life back into. After cleaning the carbs and putting in a new water pump impeller (and reinstalling the LU about a million times to get neutral and reverse) I now have it running and spitting water.

In order to keep the motor running I have to have the high idle lever full up, which leads me to two questions: How do you set the idle and adjust the throttle cable?

1) Cables - I moved the throttle lever until the butterfly in the carbs was completely closed, then I put the control lever in neutral and adjusted the barrel on the control cable until I could attach the end fitting on the cable to the throttle lever without moving the throttle lever. Is this correct?

2) Idle adjust (twin carbs) - do both carbs control the idle, or is it just one? If one, which one - lower or upper? To increase the idle do you screw the metering screw in or out? I was adjusting mine and there didn't seem to be any appreciable difference.

One last question - about the hose connection on the motor. The male connector on the motor doesn't seem to have any internal pieces (like a pin or ball) to seal the connection. The female piece on the fuel line has a ball. The result is when I unplug the fuel line, fuel drips from the male connector. I've tried looking at schematics to see I can identify internal parts, but they aren't detailed enough to answer my question. I'm wondering if someone gutted my connector at one time for reasons unknown. If they have, will this impact my motor when running, or will it just be fuel drips out when I unplug and I have to pump the bulb a few more squeezes when I re-attach?

Thanks to your postings the Ole' Merc is breathing again.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,554
Re: Adjusting idle & throttle cables, 1975 Mercury 500

Did you do a link and synch on that motor? I will guess not. Remove all but the top spark plug. Install removed plugs into their wires, tape their bases together and ground their bases to the block. Now install timing light on #1 spark plug. Remove prop and then Crank motor and adjust throttle until timing is 4-6* BTDC. Now without moving throttle, adjust so both carbs are just opening. On distributor model this is done by rotating collar on midsection of distributor, until fingers just touch carb lever. Tighten collar. Now advance throttle until timing light shows 21*BTDC. Set max spark advance set screw to stop distributor at this point. Now install spark plugs and hook up flusher. Start motor with throttle advanced, and warm engine. Now back down throttle until motor idles at 850RPM or so. Tighten idle stop set screw. Now adjust throttle cable to allow throttle to be in neutral at this point. Advance throttle all the way and adjust throttle stop set screw to stop throttle when carbs are fully open, but not hitting their stops.
 

Sidhewynder

Cadet
Joined
Dec 15, 2010
Messages
17
Re: Adjusting idle & throttle cables, 1975 Mercury 500

Link and Synch? Is that what you describe or is that another procedure? Thanks for the instructions. Much more user friendly than the manuals! I read somewhere if you don't ground the plugs or wires and crank the motor continuously it can damage the electronics. Is that true? (for future reference). Thanks!
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,554
Re: Adjusting idle & throttle cables, 1975 Mercury 500

Not grounding the plugs could damage something. Hence, that is why I recommended it.
 
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