Spark Plug/low RPM Question

[2wheelmatt]

Hey all,

I'm a bit new to boat ownership so please forgive me if I leave out any pertinant information.

I have a 1994 Maxum with a 120hp Evinrude OB off the back. The motor is a V4, 2-stroke. I was going to replace the plugs in it today and I ran into a bit of confusion. The plugs that are currently in the motor are Champion with what appears to be about a 1mm gap on them. I was looking through my service manual, and it recommends using surfaced gaped plugs. Specifically it calls for Champion QL77JC4. I believe that equates to NGK BZ7HS-10. I prefer to go with the NGK. About six months ago, I went into the only boat shop in Tucson and was given some NGK BUHXW-1. I'm not jumping to put the BUHXW-1s into the motor when the manual is calling for the BZ7HS-10s. Are these plugs interchangeable?

Also, when I pulled one of the old plugs out, I noticed that there was what appeared to be some oil on the plug. I was wondering if someone could tell me what this means.

Secondly, after a few hours on the water, the motor seems to stall at really low RPMs. This makes getting back onto the trailer a bit of a pain in the ***. When the throttle is open at any RPM above about 1300 it runs fine. I also have no problems at all starting the motor. I want to know why the motor seems to stall at such low speeds. Is this a carb issue and could it be resolved with just a cleaning, or is this related to the oil on the plugs.

Thanks,
Matt

 

[Daviet]

Re: Spark Plug/low RPM Question

Can't help you with the NGK plug question, never use them. I would suggest putting the proper champion plugs in it and see if it idles better. Could be you might need to do some carb work. What is the idle set at, 750 in gear in the water?

 

[2wheelmatt]

Re: Spark Plug/low RPM Question

Can't help you with the NGK plug question, never use them. I would suggest putting the proper champion plugs in it and see if it idles better. Could be you might need to do some carb work. What is the idle set at, 750 in gear in the water?

I'm not entirely sure what it idles at in gear. In neutral it idles around 1000 RPM.

 

[multimech]

Re: Spark Plug/low RPM Question

Use only champions, no NGK. A QL77JC4 is not a surface gap plug and I know of no Evinrudes that call for them. It is a cut back electrode plug, very common in that model of engine. There will be oil on the plugs as 2 strokes burn oil.

The dying out could be anything. A leaking carb. A leaking fuel pump into the block. See if there is a sheen on the water as you idle slowly. It could be the bleed system. It could be low compression or a misfiring spark. It could be your throttle plates not synchronized.

Hope this helps.