Mercury 500 50hp thunderbolt questions

fancy1

Seaman Apprentice
Joined
Aug 14, 2011
Messages
31
We have a 1977 Lucraft with a Mercury engine project boat and we are have issues with the engine. First its really hard to start, if we spray a little starter fluid on it , it will start good and will run fine on the muffs, goes in forward and reverse, so we took it to the water and got it running and it took off good and strong but we slowed down to turn around so as to not get far from the dock, and when we went back full throttle again it wouldn't go full throttle and it runs rough, then back at idle it idles good but a little high, and I did notice gas leaking from the carbs, and then in the water it will not go into reverse it just grinds but when on the muffs it goes in reverse fine. Its a Mercury 500 50 hp Thunderbolt Serial number 4806224. What could the problem be, any suggestions would be greatly appreciated. Thank you all for any help....:facepalm:
 

jonny_neffs

Cadet
Joined
Jun 24, 2010
Messages
27
Re: Mercury 500 50hp thunderbolt questions

Not sure about your engine issues but it sure is cool to hear about another Lucraft owner. I have a 16ft 1978 V hull with an 80hp 1989 Mercury. Your shifting may be a cable adjustment perhaps. On mine there are brass barrels on the throttle and shift cable to adjust - maybe the shifter cable is to far forward. Here is a picture of mine:

http://s751.photobucket.com/albums/xx151/jonny_neffs/Lucraft/?action=view&current=Lucraft.jpg

do you have any pictures of yours?

Good luck with your engine trouble.
jonny
 

MacDaddy21

Petty Officer 1st Class
Joined
Feb 16, 2011
Messages
280
Re: Mercury 500 50hp thunderbolt questions

Fancy,

gas leaking from the carbs means you need to rebuild your carb(s). Parts kits are available at your Mercury dealer, and are inexpensive. Disassemble the carbs and soak all the metal parts in a gallon of Chem-Dip. It is about 20 bucks for a gallon and well worth it. You can let the parts soak for a few hours, then rinse them off with water and reassemble using the new parts. Also, while you are rebuilding the carb(s), I would go ahead and rebuild the fuel pump also. It is also an inexpensive and easy rebuild. You should follow the same method as with the carbs. Disassemble the fuel pump and soak in Chem-Dip, then rinse and reassemble. I would also replace fuel hoses at this time. Fuel hose is so cheap and it is worth replacing seeing as how important it is.

When you rebuild your carb(s), I would also replace the floats, and the needle and seat. These parts are most likely the cause of the gas leak. If the float is sunk, it will not rise and seal off the needle and seat, thus allowing more fuel to leak into the carb and flood it. Also, replace all the gaskets. The carb rebuild kits come with some parts you wont need. They are sort of universal kits that are designed to fit more than one type of carb. Don't worry about the left overs, just replace what you take off your carb.

As for the rough shifting...That could be a number of things, but idle speed is a factor. Idle speed can be adjusted with the Idle Adjustment screw which is to the right of the carb. I can take a picture of mine if need be. It is basically a bolt with a rubber tip and a stop nut on it that controls how much the butterfly valve can close when the throttle is in the neutral position. Also, the shift cam linkage on the motor might be assembled incorrectly, and can cause issues as well. I've seen it happen on several motors and it is an easy fix. I can explain more about that or post a pic of mine if need be.

I would start with the carb(s) and fuel pump, and see where that puts you.
 
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