1983 Mercury 150 Blackmax 2 stoke Spark Plugs

[mtrevith]

Just got my first boat and am doing some work on the engine. The motor is a Mercury 150 Blackmax v-6 2-stroke(s/n 6621424). What I find is the plugs should be NGK BUH8. The current plugs are B9HS ( I think these are causing me some problems.

Does anyone have any recommendation on what plugs I should use?

 

[Faztbullet]

Re: 1983 Mercury 150 Blackmax 2 stoke Spark Plugs

The plugs the manual calls for is NGK BUHW or if you idle a lot BU10H, the BU8H plugs are for the newer 1 piece heads....

 

[cr2k]

Re: 1983 Mercury 150 Blackmax 2 stoke Spark Plugs

the BUH plugs are surface gap, The B9HS is an electrode style and not the right plug. Also proper fuel mixing is critical. Too much oil and the engine actually runs lean, and can carbon up.

 

[mtrevith]

Re: 1983 Mercury 150 Blackmax 2 stoke Spark Plugs

Thanks all, I ordered the BU8H today and will give them a try to see if it helps, motor just has trouble running below 2k rpm with the "wrong plugs" it sure does fly once it gets over the 2k mark.

 

[Faztbullet]

Re: 1983 Mercury 150 Blackmax 2 stoke Spark Plugs

The BU8H is still the wrong plugs for that engine

 

[j_martin]

Re: 1983 Mercury 150 Blackmax 2 stoke Spark Plugs

Thanks all, I ordered the BU8H today and will give them a try to see if it helps, motor just has trouble running below 2k rpm with the "wrong plugs" it sure does fly once it gets over the 2k mark.

Don't get too excited over the possibilities. More likely some other detail, like bleed lines, bleed check valves, idle passages in carburetors, vacuum leaks, compression, etc.

 

[mtrevith]

Re: 1983 Mercury 150 Blackmax 2 stoke Spark Plugs

Typo I ordered the BUHW, compression is good, carbs are clean just a problem on the low end with idle and starting

 

[CharlieB]

Re: 1983 Mercury 150 Blackmax 2 stoke Spark Plugs

Carb idle passages must be spotless, compressed air should be blown thru each to be sure.

Carb link and sync, idle timing, can combine and cause low speed problems.

A '9' heat range is too cold and will cause a low of low end problems.