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Found the wrong plugs installed (1979 70hp Mariner)

johanwahlberg

johanwahlberg

Member
Hi,
I ran my engine about 50 hrs or less last season. It worked perfectly fine, until the last 4-6 weeks when it started to almost stall in low rpms. It has always been a bit rough at idle up to a threshold rpm level at which it smoothens out and start spinning like a cat...
However, last weekend, I was about to change the plugs (as in a standard seasonal prep) and I had ordered the BUHW/L76V (Surface Gap, NGK heat range 12) as recommended by my service manual. I found the existing plugs were B8HS (regular gap, NGK heat range 8). I haven't had a chance to see the pistons conditions but the guy i bought it from said the compression was good.
Should I switch "back" to the recommended plug - BUHW? Can this be what's causing the almost-stalling?

See video of the stalling problem in my old post: http://www.marineengine.com/boat-fo...8542-70hp-Mariner-unstable-at-low-rpm-(Video)

IMG_7361.jpg
 
Last edited:
I've run both in mine. The gapless last longer, but the other type seem to idle better (if that's possible in a early Merc triple).

Jeff
 
fastjeff said:
I've run both in mine. The gapless last longer, but the other type seem to idle better (if that's possible in a early Merc triple).

Jeff
Click to expand...

Jeff, What engine do you have / did you run these plugs in?
How would you judge my old plugs based on the attached photo? Time to replace or ok to reinstall?

J
 
If have the choice between gapped or surface gapped plugs, I always choose the gapped plugs.

Gapless plugs work best if you operate at "sustained high speed".

Gapped plugs "should" provide a better idle and allow you to run a little more smooth at lower speeds (trolling etc).

Plugs are cheap enough that I toss and replace every second year as part of my spring prep - outboards are gas hogs, the cost of a new set of plugs can be quickly recovered if you use your boat a lot during the season.
 
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