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1991 OMC 30L and spark plugs

cdbma

Contributing Member
"Saw some good info in archive

"Saw some good info in archived discussions, but i have a follow-up. My engine calls for an RV8C (currently installed). Based on what i've read here, RV15YC4 is an appropriate replacement. What caught my eye was the phrases "older engines" and "improved idle." My 1991 Four Winns does not idle very well, despite numerous attempts to adjust, clean, curse, etc.

So, three questions. One, ok to use the 15YC4s on my setup (assuming yes) and second, what "improved" on the 15YC4 that helps with idle? Finally, what gap should I use on the 15s?

I am so looking forward to better idling - you have no idea! Thanks."
 
"You need to read your plugs!

"You need to read your plugs! Pull them all out and see what color they are running. If dark and oily, go with hotter plugs. But if they are medium to light grey or brown, do NOT go with hotter plugs.

JEff"
 
"thx for the info. my plugs a

"thx for the info. my plugs are blacker than i want - not that "chocolate brown." i've also discovered the code for champion heat range (same site as above). so, it looks like the 15s are hotter than the 8s and that must help with the idle - assumption on my part. perhaps the raw water cools stuff down too much and the engine needs a hotter plug?

i also spent some time researching my OMC setup. I have a '91 Four Winns, but the OMC Cobra apparently is a 1990, as indicated by the model number - 302BMRPWS. PWS is a 1990 designation, along with PWC and PWR. Why do i bring this up? I've been having part matching problems and i think it's because I keep saying "I have a 1991..." Also, I have electronic ignition and I think that some of the 1990 3.0L engines have points. Maybe that's what the "B" revision means in my model number. Any thoughts?"
 
Possibly you are running too r

Possibly you are running too rich (black=carbon) What temp does your gauge say you are running at? Maybe the t-stat is stuck open (assuming you have one). Looks like all 1990 3.0 had the electronic ignition.
 
"temp seems to be fine. runs

"temp seems to be fine. runs in the 160-170 range. i'm certain the t-stat is working as the temp steadily increases and then around 165 (or so), I can see the temp drop back a few degrees as the t-stat opens up.

BTW - I was looking at IPBs at Doug Russell Marine. The parts guy told me that they may have incorrect diagrams posted for 1990 and/or 1991."
 
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