intermitten fire on third cylinder

[kembry]

I have a 1974 Mercury 500 50 hp, thunderbolt ignition sn # 4073407. The motor has not been ran in the past 2-3 years and was given to me recently. After new plugs, replacing deteriorated wires (not plug wires)and fresh gas I got her started but only with at least half throttle. I ran it for about 15 minutes, shut it off and took the plugs wires off, all of the plugs were hot to the touch but the third was only warm. I checked all of the wiring and it seems to be fine. I recently purchased a service manual which is on its way, but I would like to get it in the water next weekend. Any help would be greatly appreciated.

 

[Laddies]

Re: intermitten fire on third cylinder

First do a compression ck of all cyls. then use some type of spark gap and ck for spark on all cyls then get back to us plug temp only shows that its not running full time on that cyl. could be a plug, lack of spark or poor compression

 

[kembry]

Re: intermitten fire on third cylinder

Laddies,<br /> I have switched that plug with others and nothing changed. Without a guage compression seems to be the same as the other cylinders, but I'll get one to make sure.

 

[kembry]

Re: intermitten fire on third cylinder

Compression Test Results: Preformed with manual pull rope.<br />1. 90 <br />2. 90<br />3. 80 <br />4. 90<br />Spark plugs wires were tested and all have good spark. I believe that these wires may be original. I took the boots off of two of the wires because my tester would not fit all the way in. The clasps? were basically sitting on top of the stripped wires with part of the clasp that actually punctures the wire through the side. Is this normal, or should I update the clasps? Once I finished testing the wires and cyl. I put everything back together and started her up. (I noticed that the choke by the ignition switch sometimes does not work, need to check wire connections.) Now it sounds like its sputtering or starving for fuel. Once I pump the bulb untill it is hard I can get it started and will run for a second and die. when I go back to the bulb its not as hard as when I left it. After I finally get it running for a moment I go back and pump the bulb again. It seems as though I might have a fuel problem. The bulb will not stay hard. The gas vent is all the way open. I have an inline filter between the tank and the bulb. I guess I'm not sure how "hard" the bulb needs to be. I can pump it untill fuel is coming out of the carb overflow. One of the fuel lines inside the cowling looks brand new, the other has weathered but i don't see fuel leaking out. If its a pin hole in the line, how can I tell? It shouldn't matter where the filter is right? Thanks in advance for all the help, you guys are great!!

 

[Laddies]

Re: intermitten fire on third cylinder

The compression isn't great but the rings are probably sticking alittle from setting around I like to use powertune from mercury to free them up (shortly you will be getting a sales pitch on brand X I'm sure) With what you describe I would clean the carbs put a fuel pump in it and run it with extra oil 24 to 1 for a tank of fuel and see if it don't straighten out the problem

 

[kembry]

Re: intermitten fire on third cylinder

Would the compression test diffrently by turning it over with the key? By fuel pump, do you mean the bulb? I know that the carbs are synchronized, impossible for rookie to clean them myself?