79' 70 HP Evinrude - new plugs idles very fast

[30nomore]

I replaced the plugs in my 79' 70 HP Evinrude. They were Champion L77JC4, but I replaced them with Autolite 2634. It now idles way-way to fast. Fast idle is down/off. The gaps looked the same between the plugs. The plugs call for .03. I had read on a forum that somebody else had a fast idle problem after he tuned his boat, but no one could figure it out. I think its the plugs. OMC requires Champion and does mention that other plugs will cause mis fire, which sounds like mine might be doing at fast idle. The only other thing I did was check my compression. I did not however ground the plugs but I did put the plugs in the wires and laid them aside. Does anybody have a good opinion?

 

[GeneH]

Re: 79' 70 HP Evinrude - new plugs idles very fast

Should you slip the old plugs back in and see if the idle returns to the old speed? This would prove the new plugs are the cause, not something else.

 

[30nomore]

Re: 79' 70 HP Evinrude - new plugs idles very fast

Good idea, but I'm a blockhead. I used two of the old ones to make a better screw in plug apparatus by removing the inner stem of the plugs to attach to the compression checker. I got a good compression check I didn't anticipate anything out of the blue to change to a worser state. I'll see if the local marine shop has a couple of used ones to check.

 

[30nomore]

Re: 79' 70 HP Evinrude - new plugs idles very fast

I replaced the autolite 2634 cross reference plugs with new OMC Champion L77JC4 plugs. It now idles slow again, but runs pretty rough and mis fires. Before it idled and ran pretty good. So the fast idle was due to installing the cross referenced Autolite plugs! Nice call GeneH!

When I checked my compression I did not ground the plugs. I removed all 3 plugs and put the plugs back into the wire, laid them aside, and opened the idle throttle, then checked each cylinder which all were within 10%. Did I fry something by not grounding the plugs? Because it did idle and rev up good.

 

[HighTrim]

Re: 79' 70 HP Evinrude - new plugs idles very fast

Are the plugs torqued to spec? Probably 17.5-20.5 ft/lbs. Have you done a spark test to ensure they are all firing? Do that first and let us know what you find to further troubleshoot.

 

[30nomore]

Re: 79' 70 HP Evinrude - new plugs idles very fast

Thanks HighTrim - I regapped the plugs to .030 and tested the spark jump, which was good in 2 cylinders, about 1/2' blue spark. Number three seemed a bit short around 3/8" and did seem orangish blue. I torqued all 3 plugs to 18 ft/lbs. I also ran it and pulled each wire individually, and all three reacted the same, ran rougher. I also replaced the gas and oil mixture 50:1 to be sure it wasn't the gas/oil.

The motor does idle down now but won' stay running at low idle and it still seems to run rough. The OMC plugs and the ones I pulled were gapped around .035 and higher. It does start right up, just the rough and stopping anywhere near low idle. There is a spurt/sputter about every 5-10 seconds at medium to higher idle (no low idle).

I'm curious if the throttle/shifter box has a short in it, or a throttle cable slip and if that may cause this?

Also, I drained the carbs and sprayed carb cleaner up into the high speed valve stem (I think) and then flushed the carbs.

 

[HighTrim]

Re: 79' 70 HP Evinrude - new plugs idles very fast

When were the jets and carb last rebuilt/cleaned.?

 

[30nomore]

Re: 79' 70 HP Evinrude - new plugs idles very fast

I'm not sure, but it sounds like I should. I've had the boat since spring and it ran great, well I did have some trouble starting the motor after running and then stopping and then restarting. It seemed to flood. In fact the reason I changed the plugs was the last time on the water a week ago, me and two of my daughters had to row about a mile before it restarted. Thats why I changed the plugs and when big trouble really showed up.

Where would be a good place to order three carb kits, here at iboats?

 

[30nomore]

Re: 79' 70 HP Evinrude - new plugs idles very fast

I rebuilt the carbs and it does idle down but still spurts and stalls every once and awhile. THe boat seems to shake now when idling. I posted a new post about the fuel filter pump. It states in the manual that this may cause such.

It baffles me that just a compression test and spark plug change can open many cans of worms.

 

[iwombat]

Re: 79' 70 HP Evinrude - new plugs idles very fast

Not grounding out your plug wires may have started the whole mess. If there was a loose or bad connection it probably charred it up good. You may want to replace the plug wire on the cylinder that had the weak spark.

You may also want to clean up all the grounds on your coils while you're at it.

 

[30nomore]

Re: 79' 70 HP Evinrude - new plugs idles very fast

Thanks Iwom, I think you just confirmed what I've been pondering on. It was the next thing to do, that was to buy at least one new ignition coil. Replacing the wire may be easier. I'll check it first thing in the morning as well as check all their grounds.

 

[30nomore]

Re: 79' 70 HP Evinrude - new plugs idles very fast

The spark plug wire, coil side, is encased in the ignition coil. It looks like I need the ignition coil which comes with the plug wire.

The OMC coil assembly # is 0581998 found on BRP. Seirra list my motor with a coil part # 18-5176. On another web site that seirra coil part number is listed only for a 115 HP.

My question is; Is this 18-5176 the right part cross referenced number, and will it work by just replacing the weaker sparked coil, or will I will I need to replace all three coils since it's new? Or, is there something else that causes the weaker spark? Thanks

Also, do I splice the coil lead wire between the coil and connector, or is there a way to replace the coil lead wire within the connector?

 

[iwombat]

Re: 79' 70 HP Evinrude - new plugs idles very fast

Those plug wires will come right out of the coils if you tug hard enough. The replacements will slide right in with a little bit of lubrication like soapy water. They look like they're firmly in place. Looks can be deceiving. I replaced all mine last year on a similar set of coils.

 

[30nomore]

Re: 79' 70 HP Evinrude - new plugs idles very fast

they do pull out - thanks. I did order one new coil before I read the last post from Iwom. I want to replace the other two plug wires while I'm at it. I looked for them but can't find just the plug wire.

The plug wire has stamped on them "Pretolite 108717 7MM.

Are there universal plug wires? I know that the wire resistance needs to be the same, I think.