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Surface Gap Plugs-are they good or better or necessary if that's what your motor calls for?

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bentonparkwest

New member
I have a new used 1981 Johnson 150 HP. It calls for UL77V plugs with no gap. It has other plugs with a gap in it now....don't have the part no. but they aren't surface gap plugs...
What should I use instead of the UL77V and does it make a difference? Why use/spec surface gap plugs?
 
The surface gap plugs last just about forever, however, they are a cold running plug regardless of their stated heat range which does make them prone to fouling.

The alternative and most recommended plug by many is the Champion QL77JC4 electrode type plug. The original recommended gap setting was .040 but has been changed to .030 at some point in the late 1990's. One gap setting or the other may result in improved performance, either at idle or full throttle (try both settings).

It has been found that some engines will not run properly on anything but the surface gap plugs for some reason but this happening is few and far between. Personally, I recommend the Champion QL77JC4 plug.
 
Thanks for the info, but can you tell me why you say this? Reference?
The QL77JC4 plug is for the newer model engines and the Gap calls for .030 setting. This contradicts your .040 and wouldn't the piston come close to hitting the plug?
I read that surface gap plugs are more high performance when specified.
I don't know...
Just trying to figure it out. I need to pull the plugs in it now and see what's in there.
I ordered the UL77V's already and they are more expensive....does that make them better?
I'll try both and see what the difference is if you are sure they will interchange.
Thanks,Bent
 
Just take it from experience , and lots of it !!!!!! ---------Use the QL77JC4 in your motor.---------------And do not worry about a piston hitting a plug.----------------
 
The surface gap plugs have some advantages and some dis-advantages.
- The spark is always 'free' and consistent during the life time of the plug.
- Plug lifetime may be up to 10 times of a 'normal' plug.
- next to no risk of the plug turning into a 'glow-plug' causing pre-ignition and piston melt down.
They are however mainly intended for 'hard' running, high compression engines.
Downside is mainly poor idle characteristics.
As alternative to the UL77V, you may try the QL16V which has improved the idle characteristic but is still a surface gap plug.
For extended trolling and low idling, you may use the above mentioned (Q)L77JC4, but that might however be a bit short lived if ran hard.
Which plug to use has a lot to do with what you are using the engine for: Trolling or water skiing??
 
Benton.... The QL77JC4 plug has been in use for many years, dating back to 1973 anyway, the original gap setting then was .040, recommended by OMC. There's no danger of it hitting the piston.
 
Joe haffiman racer...i got a question....i just got rid of a 94 model evinrude 90 for other reasons....a good mechanic told me he was surprised i had never dropped a power pack in 18 years on a heavily used motor....i got to thinking later...could it possibly be because i changed the plugs every 2 years?..sometimes every year.....no indication of a problem..maybe a little rougher idle when it was cold...ql77jc4 plugs was all i used....
 
Plugs are parts of a chain in an electronic system. Change them out of spec, and you might experience some other component in the system to fail, most likely the power pack. Lifetime of a 2-stroke plugs may vary, all from as low as 20 hrs and up to around 100 for conventional plugs like the QL77JC4. They may still look ok, they may still spark, but internal resistance and voltage needed for the spark to jump may change. Normally a lot cheaper to change plugs from time to time than a power pack!
 
Powerpacks are often changed as a last hope to improve operation of a motor.----------Easy to change and a scource of revenue.------------Picked up a GT 175 some years ago and it came with a box of electrical spares ( 2 powerpacks , stator and timer base )---------------Found that the real reason of engine running problems was mechanical ( scored pistons )--------------Trouble shooting is becoming a " lost art "---------------Powerpacks are changed all too often !!
 
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