1978 Mercury 500 questions...

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weasel897

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Feb 7, 2012
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Hello all.....I recently bought an 85 bass tracker with a 78 mercury 500 on it.

The motor starts and idles fine. Everything seems to be running well(as far as I know about outboards anyway). I've replaced the impellar and the gaskets that are associated with that. I also changed the LU oil. I plan on going through the carbs to check for anything out of the ordinary.


Questions:
1. what else should I perform on this engine before really using this engine?
2. I put her in the water for a quick test and the shifting in and out of gears seems fine, but there is little to no power at WOT. What could cause this? I opened up the Mercontrol box to make sure that all levers and cams were intact. (All appears well other than the 30+ years of wear). There seemed to be loads of slack in the throttle lever. I had to put it almost all the way forward to get it engage the throttle on the engine. Any thoughts?

Thanks for your help!
Brian
 
sutor623

sutor623

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Messages
4,087
Re: 1978 Mercury 500 questions...

weasel897 said:
Hello all.....I recently bought an 85 bass tracker with a 78 mercury 500 on it.

The motor starts and idles fine. Everything seems to be running well(as far as I know about outboards anyway). I've replaced the impellar and the gaskets that are associated with that. I also changed the LU oil. I plan on going through the carbs to check for anything out of the ordinary.


Questions:
1. what else should I perform on this engine before really using this engine?
2. I put her in the water for a quick test and the shifting in and out of gears seems fine, but there is little to no power at WOT. What could cause this? I opened up the Mercontrol box to make sure that all levers and cams were intact. (All appears well other than the 30+ years of wear). There seemed to be loads of slack in the throttle lever. I had to put it almost all the way forward to get it engage the throttle on the engine. Any thoughts?

Thanks for your help!
Brian
Click to expand...

You may be lucky then because you might just need a throttle cable. Take the cowling off the motor, push the throttle lever forward all the way and see how advanced the timing is, and how far open the butterfly valves are on the carbs. If the valves arent fully opening, then you have found your problem. Id also check compression just to make sure that is in spec. While you are in there you can clean up all the major wires and ends, especially to the starter. I would take the distributor cap off and clean up the rotor button and cap leads. I went ahead and changed all my plugs and wires just for kicks. (on my 650)
 
sutor623

sutor623

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Re: 1978 Mercury 500 questions...

Also, you said you plan on going through the carbs to check all that out. Getting to these carbs is a BEAR and if you are going to "check them out" you should just do a full carb and fuel pump rebuild, and change out any bad hoses. Otherwise, if it starts, idles and runs well (once you fix the throttle cable) I would run some seafoam through her and call it a day. Depends how soon you want to be out on the water though. Can never hurt to do a decarb and change fuel pump diaphrams. I had to change my hoses when I did it though because they were so old that they couldnt handle me fidgeting with them without breaking open, so beware.
 
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weasel897

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Joined
Feb 7, 2012
Messages
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Re: 1978 Mercury 500 questions...

Thanks for the quick reply!!!

I'll check the throttle cable again tonight(weather permitting). I'm hoping that's the main cause of my problem, but if luck has anything to do with it, I'm gonna be replacing everything but that! :facepalm:

Good point on cleaning up the wires and replacing the plug wires. Plugs and wires are usually the first to go when I buy a new toy anyway...

I am going to go through the carbs and fuel pump because the top one has a small leak and with gas prices....well...ya know!

Any other "gotchas" that I should look for on this used engine?

Thanks again for you help!
Brian
 
sutor623

sutor623

Rear Admiral
Joined
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Messages
4,087
Re: 1978 Mercury 500 questions...

Glad to see you are going to service this thing like you are supposed to. If you are leaking then more then likely you need to set the float height of the carb. Other than that, check all the starter connections, change water pump and L/U oil, and take her out!
 
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weasel897

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Joined
Feb 7, 2012
Messages
12
Re: 1978 Mercury 500 questions...

Checking and replacing things now make me worry less about running into trouble on the water. Id rather wonder why the fish aren't biting or the ducks aren't flying than wonder why my engine won't start.

Plus I like to feel like I know how my stuff works before putting it through it's paces.

That and the PO stated his kid "played with the carbs and linkage"!!!:facepalm:

Thanks,
B
 
sutor623

sutor623

Rear Admiral
Joined
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Messages
4,087
Re: 1978 Mercury 500 questions...

Yeah trust me I have been dead on the water, because my motor "ran great in the driveway" The SOB wouldnt start while actually in the water, and the next trip out it wouldnt idle while in gear. This is also why I dont like to sell stuff once I have had my hand on it. It is always nice to actually KNOW whats been done rather than believing the previous owner.
 
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