1988 Mercury 60HP

[pickard1]

Hi folks,
Took a chance and bought a Merc that sat a couple of years. Drained most of the old gas from the carbs and started it yesterday using high idle. I was able to lower the idle speed but the engine would misfire and it would stall at the lowest idle. Shot some carb cleaner into the two carbs but the misfire continued. Today, I pulled the plugs and checked the compression. Top cylinder was 120, middle was 130 and bottom was 130. I shot in some WD40 and the top one got up to 122. As for the plugs, the top one was baked Jet black. The other two were 'normal' looking (not white or black). I replaced the top plug with a new one and put the same plugs back in middle and lower cylinders. I started it just to burn off the WD40 and it ran better but still misfired and would stall at lowest idle. Tomorrow, I am going to replace the fuel filter and put new high octane gas in my tank along with some SeaFoam. Keep in mind that I only ran it a few minutes and there was smoke rising from the exhaust (likely the gas/oil I was using was also an old mix, regular octane).

Any thoughts on the black plug or the misfiring?

Can I test for a decent spark without some fancy meter or tool?

Would any carb adjustments help with the misfire?

Cheers

 

[SparkieBoat]

first off carb cleaner sprayed in the throat of a carb will do very little, you need to take your carbs apart and spary out the main jets and the needle valve passage and the idle passages. second, the proper test equipment is cheap enough. pretty much everything you need for under $100. saves you time and money and guess work. follow my sig below for more help. you can also google reading spark plugs for lots of ways to tell things from your plug condition/color. also do a search on how to decarb your engine, seafoam works great and may help restore your compression on that low cylinder.

 

[pickard1]

Thanks S B! I will try everything you recommended.

 

[emckelvy]

Here's a "quick & dirty" carb clean that sometimes works if you just have some material lodged in the idle circuit: remove the silencer assy in front of the carbs so you'll have access. Turn the idle mixture needle clockwise until lightly seated, count and record how many turns that took.

Then, unscrew and remove the idle mixture needle and spring (#'s 7 and 8 on the attached diagram) and spray carb cleaner into the idle mixture needle passage. This may clean out any offending debris. Reinstall needle & spring, set it to the # of turns that you recorded earlier.

Do the same to the 2nd carb, put 'er back together, and maybe you'll save yourself some carb work. If not, you're gonna have to take the carbs all apart anyway; nothing to lose.

BTW, there's no telling what the P.O. did to the idle mixture adjustment in the first place, so you might try some adjustments and see if it idles better. Best way to do that is with load on the motor, so you could put it in a plastic barrel and first adjust for best idle, plus about 1/2 turn CCW on each needle past that point. If you can get it to run in the bucket in gear, warmed up, adjust for smoothest, highest idle and once you find that point, turn each idle screw about 3/8 turn CCW (to the rich side). That should be pretty darn close to what you'll need once you get 'er in the water for a final tweak/tune.

HTH & G'luck........ed