NGK Spark Plug Symbols


What spark plugs are you running in your Mercury 150 HP 2.0 Liter Black Max outboard? This handy chart from NGK provides the codes or symbol key so you can determine which plugs are in your racing outboard.

Download free the NGK Spark Plug Design Symbol Chart here: NGK Spark Plug Chart.

007's picture

You can check this chart for a similar plug with an "R". Also, 180 psi compression sounds very high for COR motor. Most strong COR motors are around 145 psi. Maybe double check the gauge, but if they are all about the same, most likely that is not the reason why the motor might be off. The fact that one plug was clean... that has to be your problem. Maybe the spark works until the vibration of motor causes a wire that is loose not to fire? Or maybe check the carb for that hole, which old be opposite side, to make sure the main jet is not clogged.

Wow 145 lbs This great motor i got from Tony i ran a comp check on it an it only has 120lbs mmmmmm so i tried a different gauge an yep the same. looks like this motor needs a rebuild damn the luck.So a good COR motor should be at least 130 to 150 comp?

007's picture

Higher port heights, elevation, less oil, temperature etc, might equal lower compression numbers. My motor at Parker this year had higher port heights and the fresh motor only pulled 110-125 psi. If you pull the head, measure the port heights from the deck and compare them to stock.

Capnzee88's picture

130 seems a little high for a "stock" 150 V-6 while 120 seems a little low for a COR engine. As Mike said, his engine, built specifically for the Parker Enduro , had raised port heights which lowered the compression. My engine, right off the bench of one of the "renowned" local engine builders was 135. I "squawked" until I checked the port height. The ports have been raised and my engine runs down the straight with any of the COR boats. On the other hand, my "stock" SST 120 engine runs 150 psi with 26cc heads and regular gaskets, seems as fast as any of them I have tried. You might want to give your Tony engine another look unless you are simply looking for a winter project.

STV_Keith's picture

Run a leakdown on it. >8%, it needs to come apart.


yes did that already. it needs to come down. I just got a 1980 150 hp never been torn down an the comp on it was 130 across the broad. I thought 120 lbs was low. Thanks Keith an Mike for the im foe