Merc 1150 inline 6 no power from cylinder 3 or 4 plus water on #3 plug

Hey folks ... I need help ... I have a 1978 merc inline 6 .. problem started with stuck float on carb #2 ... or so i thought ... symptom was lose of power(ignition failure) on cylinder 3 and 4 (plenty of spark) and gas spitting from carb #2. Rebuilt carb ... replaced plugs .. cylinders 3 and 4 still seem weak ... went out on river .. engine now has no low end ... top end is fine. Tried setting idle on carb two (from 1 1/2 to 2 1/4 ) ... no luck .. back home ... checked compression .. all 6 cylinders in 130-140 range... swapped carb 2 with carb 3 .. ran with muffs ... still no power on cylinders 3 and 4 .. pulled plugs ... OUCH .. water (milky substance) on plug #3. Rest look ok. Forum posts pointed at possible water jacket leak .. installed new water jacket cover and all 3 associated gaskets ... still have water on #3.

Question #1 ... is the power (ignition failure) on cylinders 3 and 4 due to lack of compresson at low rpm's due to a reed problem??

Question #2 ... does the water leak on #3 indicate a cracked block or cylinder head or could it possibly be sucked in through exhaust ports due to reed being stuck open .

Re: Merc 1150 inline 6 no power from cylinder 3 or 4 plus water on #3 plug

you might have a bad gasket on the exhaust plate. you will have to pull the powerhead to replace it and you might as well put new seals in the upper and lower endcaps as well.

Re: Merc 1150 inline 6 no power from cylinder 3 or 4 plus water on #3 plug

Often the inner exhaust cover or the baffle plate develop holes. This allows water to enter the cylinders and put out the spark. if you are finding either water drops or steam-cleaned spark plugs, it is likely water is entering the cylinders. If it is the lower cylinders, it might be bad crankshaft seals, however, if it is mid or upper cylinders, it is likely leaky gaskets or leaking covers or baffles.

The idle issue sounds like a dirty or misadjusted carb.

Re: Merc 1150 inline 6 no power from cylinder 3 or 4 plus water on #3 plug

Hey guys ... thanks for the replies.

Due to several posts on forum about water leaks on #3 cylinder on this model engine, I replaced the water jacket cover, water jacket cover gasket, cylinder block to baffle plate gasket, and baffle plate to manifold cover gasket. At that time, visual inspection of the baffle plate seemed to be OK. After only several minutes idleling on muffs, plug #3 was milky white again. Maybe leak is due to a possible pin hole in the baffle plate. Note that all other plugs seem ok(slight oil residue on each).

Still no idea why cyclinder #4 is not firing !!

Ssuspect that cylinders #3 and #4 reed valves are not working correctly at idle. Could it be possible that the defective reed is allowing water to be sucked into the #3 cylinder??.

Re: Merc 1150 inline 6 no power from cylinder 3 or 4 plus water on #3 plug

Could it be possible that the defective reed is allowing water to be sucked into the #3 cylinder??.

Click to expand...

Yes....

Re: Merc 1150 inline 6 no power from cylinder 3 or 4 plus water on #3 plug

You also need to closely inspect the inner water jacket cover. It has many nooks and crannies. It can and does rot out in the nooks and crannies, and then leaks water into the cylinders.

Re: Merc 1150 inline 6 no power from cylinder 3 or 4 plus water on #3 plug

Hey guys ... thanks for the quick replies.

Since I replaced the inner water jacket with a new one and visually inspected the exhaust baffle plate during that process with no sucess and the fact that several folks agree that defective reed valves for cylinder 3 and 4 could be causing the water on #3 plug and also dropping cylinder #4, it looks like I've got to tear down the power head and replace the reed valves along with gaskets, seals etc...

Before I 'bite the bullet', is there a test or procedure I can try to prove the reed valve(s) are defective.

Re: Merc 1150 inline 6 no power from cylinder 3 or 4 plus water on #3 plug

Sure, Reed valves are one way. See if you can pull air out of the middle carb. If you can the reeds may be defective. They aren't meant to seal perfectly, but you should be able to tell if they are good.

Unfortunately, the only test I can think of will give you gas breath......