Spark Plug Picure - Diagnosis Please

[OCboat]

1976 Merc 500 - SN 4577xxx. This motor came with a 1959 Glasspar G-3 that I plan to restore some day but I thought I would get the motor running and put it on my 14' runabout. It has been sitting for a couple of years so here are the things that have been done to date. It was only getting spark on the bottom two plugs so I followed the CDI troubleshooting guide and determined that my switch box was bad. I replaced the box and now have good spark on all 4 plugs. Compression is an even 130 on all four cylinders. New plugs are NGK BUHW-2. I removed and disassembled the carbs, soaked everything in Berryman's chem-dip (minus the rubber and plastic parts) blew out everything with compressed air and reassembled with new carb and fuel pump kits. After everything was put back together, it ran great for about 3 minutes, then it started stumbling and running very rough. It eventually stalled and then it would not start again right away. It will start back up and run rough after it sits for a while. I pulled the plugs after this 3 minute run and this is what they looked like. Plug number 1 is on the far right and plug 4 is on the far left. #1 is almost spotless with a faint coating of gas. #2 is covered in dry carbon. #'s 3 has a lot of wet carbon around the electrode and 4 has a wet oily appearance. Can anyone offer any advice on what may be wrong and any suggestions on what to do next? Thank you.

 

[GA_Boater]

Try moving the plugs around. Maybe the one in #2 is breaking down. Or pick one of the old ones to stick in #2.

 

[OCboat]

I cleaned all the plugs and then switched #1 with #2 and #3 with #4. It looks like the problem is still with #2, not much different from the first picture. I checked for spark again and I'm getting a 1/2" blue/white spark on all four plugs.

 

[GA_Boater]

Instead of leading you astray, I'll let some of the more knowing help you from here, OC. Your motor is too new for me. :smile:

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One seemly running bad out of four. And #1 seems to be the cleanest and #2 the worst. Here is one thing to try. Set the idle needle to 1 1/14 to 1 1/2 turns out from lightly seated. Maybe the needle needs some fine tuning?

 

[OCboat]

Thanks for the suggestions GA. It's almost like #1 is doing nothing and #2 is running extremely lean. Since I'm seeing a good spark on both wires and I cleaned the carbs, I'm not sure if it is a spark or fuel problem, or something else.

 

[GA_Boater]

When I rebuilt my carbs, the lower gave me fits getting the float adjusted right. I could adjust the needle on the upper and RPMs raised and lowered as I closed and opened the needle. The lower had no affect, I could close it and almost take it out. Once I got the float right, top and bottom needles both changed RPMs and I was able to find the happy point adjusting them. Worth a try, OC. Good luck. Let us know.

 

[OCboat]

Took the carbs apart again, cleaned thoroughly, and set the float per the instructions in my Mercury Service Manual. Adjusting the needle on both carbs makes a little difference but it running so rough that it is hard to fine tune. I got the motor to run for a good 10 minutes but when I pulled the plugs, they looked the same as the above pictures (after cleaning them off and switching them around). I'm going to swap the coil on #2 with another one to see if the problem follows the coil. Anybody have any other suggestions?

 

[OCboat]

I purchased a timing light and determined that cylinders 1,3 and 4 were firing at the TDC pointer but #2 was firing 180 degrees from the TDC pointer. Does this point to the trigger being bad?

 

[Chris1956]

In the first picture, it appears the top carb is flooding a bit. Not too bad. The bottom carb is flooding a lot, and the lower crankshaft seals are allowing water to get into cylinder #4. Not sure about your ign firing question. You do need to fix the lower crankseals.

 

[OCboat]

Thanks Chris. Is that because the plug is so clean? If so, that is the #1 top cylinder. The order is from #1 right to #4 left.