Could these new spark plugs cause rough running? (pix)

[motomania]

------Scenario
My engine is an 86 150 Evinrude (model # E150STLCDC) and the factory service manual calls for Champion plugs, yet the part # has been updated, and apparently the plugs have too. The pic of the shorter plug is of the correct plugs called for (same part # in factory service manual), the longer plug is the new part # Champion has listed. I've checked and double chacked, and the new plugs (longer ones) are the correct ones listed by Champion to replace the originals.
-Yet when I put the new plugs in (torqued them to spec), my engine would not even stay idling, and when it would stay running, it stumbled like it was misfiring.
-I'm going to go back out tomorrow with the original plugs and see what happens.
-------Question:
-Could the longer length of the new plugs cause the rough running? (I was thinking it may mess with the timing or something)

[SEAHORSE]

The longer reach surface gap plug (QL16V) is for commercial high speed use and gives a long plug life, unlike the J gapped plugs. Because of the surface gap design, idle is not always the best and is really bad in some motors. They are also fairly expensive.

Your best bet, assuming that your motor is healthy as well as the ignition system, carbs, and related items, is to use QL77JC4 plugs gapped at .030'. They last about 100 hours and that is the same interval that your motor needs for routine service and tune ups.

[motomania]

-Thanks Seahorse!
-That would help explain why the engine ran fine before changing the plugs. I was only changing them as I had no idea how long the shorter ones had been in the engine. (boat/motor were recent purchase)

[rudetech1]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SEAHORSE &raquo;</TD></TR><TR><TD CLASS="quote">The longer reach surface gap plug (QL16V) is for commercial high speed use and gives a long plug life, unlike the J gapped plugs. Because of the surface gap design, idle is not always the best and is really bad in some motors. They are also fairly expensive.

Your best bet, assuming that your motor is healthy as well as the ignition system, carbs, and related items, is to use QL77JC4 plugs gapped at .030'. They last about 100 hours and that is the same interval that your motor needs for routine service and tune ups.</TD></TR></TABLE> You got that right!!! Sounds like a Rusty post!! Gapped plugs work soooo much better!!!!

[motomania]

-Gapped plugs work much better? ....... Seriously? I had no idea.
-I was just following the factory service manual, but I'm always open to suggestions or better ideas.
-
-Why do they work so much better?

[rudetech1]

There was a revision on some of the engines.