Old Mercury 500 50hp Motor

[grumblefrogg]

I am hoping someone can help me.<br /><br />A few years ago, my brother and I bought this old boat that had a Mercury 500 Thunderbolt 50hp motor on it. <br /><br />The motor worked great until about a year ago, when the starter went out. We took the boat to a well known mechanic that specializes in old Mercury motors (an old-timer), and he stumbled on other problems that were fixed or replaced (rebuilt starter, tune-up, replaced wiring harness, replaced water pump, repaired the Control Box harness).<br /><br />After all that, it kept stalling.<br /><br />We took it back and he said the carburator needed fine tuning. He worked on it and we took it out on the water again, This time it seemed to lack power. We took it back to him one more time, and still the problem could not be resolved.<br /><br />I am hoping someone can steer me in the right direction with a possible problem of this old motor.<br /><br />Here are the specifics:<br /><br />S/N 3012567<br />Mercury Thunderbolt 500 50hp outboard.<br /><br />Symptoms:<br /><br />Lack of power. Used to go 15-20 mph without any problem. Max speed now is about 5 mph.<br /><br />Seems to be burning a lot of fuel. <br /><br />I am hoping someone can help me.<br /><br />Thanks in advance.<br /><br />Timbo-

 

[tmcalavy]

Re: Old Mercury 500 50hp Motor

Check the fuel pump. Take the cowl/cover off and watch the fuel pump while it runs on the muffs or while you have it in water. It may drip, drip, drip or it may not. For $10 or less in parts (including shipping), I'd replace it. Then check your plug wires. I accidently reversed 3 and 4 once and my Merc 500 ran just like you describe. If that doesn't do it, I'd consider paying for a link and synch from another mech.

 

[grumblefrogg]

Re: Old Mercury 500 50hp Motor

Thanks for the advise, Tim Mc.<br /><br />I'll take a good look at the fuel pump and check out the plug wires.

 

[izuizme]

Re: Old Mercury 500 50hp Motor

If you plan to keep this motor might as well check the compression if #'s are good it may be worth it to rebuild the carbs.I just did for about $130. I have the same motor and have no regrets...!! moving my 14 footer at 30 mph..GOOD LUCK & PS buy nthe shop manual

 

[The Marine Doctor]

Re: Old Mercury 500 50hp Motor

I assume your old 50 has a distributor?<br /><br />If so is it hard to start?<br /><br />Check the timing.<br /><br />TMD

 

[NathanY]

Re: Old Mercury 500 50hp Motor

You said that the motor is using excessive amounts of fuel, I would then check the floats in the carbs to make sure that you are not getting too much fuel. Remove the plugs and see what they look like.

 

[grumblefrogg]

Re: Old Mercury 500 50hp Motor

Thanks for all the tips, everyone.<br /><br />I guess I'm gonna have a busy weekend

 

[sharkcat]

Re: Old Mercury 500 50hp Motor

Hi froggie,what everyone else said is relevant but there is one thing you should do first & that is get a manual.It will tell you how to do all the things that have been suggested.I would think you have a cylinder or 2 that arent firing.Check the plugs/firing order.Clean the fuelsystem,reset the float levels.Do a link & sync & you should be good to go.Good luck

 

[grumblefrogg]

Re: Old Mercury 500 50hp Motor

10-4 on the manual, Sharkcat.<br /><br />I actually already have one. I just didn't know where to start, but thanks to you all I now have an idea.

 

[greasemonkeyozi]

Re: Old Mercury 500 50hp Motor

I noticed that when resetting floats, you cant really go by the manual, but you have to go by the floats themselves. I had replaced my floats and the package it came in had a card with settings that were totally different than the manual.

 

[Bitmess]

Re: Old Mercury 500 50hp Motor

Did you get it fixed?