79 25hp 1 spark plug foulling

[DCC]

i have a 79 25hp evinrude 2 stroke 2 cyl foulling lower plug and idles rough. have tryed to clean carb and tryed to ajust air fuel mixture several times with no results also have replaced coils and checked spark day and night also checked compression and has 130 psi on each cyl and have checked reeds and look fine no cracks chips bends or corrosion runns perfect once off idle any help? thank you

 

[AlTn]

Re: 79 25hp 1 spark plug foulling

two quick checks...not sure which cylinder provides the pulse for your fuel pump, but unscrew the fp from the block leaving the line from the tank connected, disconnect the line to the carb and place our finger over the outlet nipple. Pump the fuel bulb from the tank and see if even a small amount of fuel is leaking from the rear of the fp where it attaches to the block. If so, it may be leaking unmetered fuel into the crankcase causing the lower plug to foul. The other quick check is to unplug the amphenol plug that goes from the power pack to the coils and check that the pins and female connections are tight and corrision free. If they look good and are tight, then you need to check the dva voltage from the pp to each coil which should be 150V or more with motor running.

 

[DCC]

Re: 79 25hp 1 spark plug foulling

checked fuel pump and is ok and checked voltage going to coils and was 99-125 at 1000-1200 rpms book says that motor should idle around 700 rpm my will not idle that low with this problem do i need a new power pack or more testing?

 

[14ftgrumman]

Re: 79 25hp 1 spark plug foulling

Did you test the spark with a spark tester and check compression with a compression tester?

 

[AlTn]

Re: 79 25hp 1 spark plug foulling

using the spark checker...it should jump a 1/2" gap on both plug wires as you pull the rope with the plugs out...this may require another observer or rope puller as it's hard to do both at the same time..dim lighting conditions help as well...post back results

 

[DCC]

Re: 79 25hp 1 spark plug foulling

i did use a compression tester but not spark tester will have to try after week end busy rest of week thanks for help

 

[DCC]

Re: 79 25hp 1 spark plug foulling

checked spark with spark checker and set gap at 1/2 inch had no problem seeing bright blue spark jumping gap also had crisp snapping sound. Any more thoughts? thank you

 

[AlTn]

Re: 79 25hp 1 spark plug foulling

hmmm..sounds like you have plenty of spark...if you aren't already, try champion L77JC4 plugs gapped at .035 or .040....030 is the called for gap but maybe that lower cylinder needs it a little wider, especially if you troll with it.Next up...get an inductive timing light and check for a bright,even, flash on each plug wire as it idles...if this checks out fine..you can rule out ignition problems...link and sync will be next up.

 

[DCC]

Re: 79 25hp 1 spark plug foulling

tryed inductive time light looks even on both cyl. not sure why differnt plug now have had this boat motor combo fo over 11 years and has been in family since was new. since i have owned it i have ran a ngk b7hs gapped at .030 because that is what was in it when i got the boat and my dad had it serviced at well known evinrude dealer when he had it. but will try to pick up new plugs(L77JC4) thank you for all your help so far THANK YOU

 

[AlTn]

Re: 79 25hp 1 spark plug foulling

looks like with that history the ngk's are working for you...go to the Top Secret Files and read TD's steps on the decarb procedure...seafoam makes a spray now " Deep Creep" which makes it easier to spray into the spark plug holes and carb throat...you'll need a can of seafoam as well to mix with 3/4 gal. of fuel mix...after decarbing see how it idles, you may have to put new plugs in afterwards...if still acting up at idle...it's back to that carb for tear down, clean, and rebuild...unsolicted advice...take pics of carb linkages before you begin to remove it from the motor...I realize you've had it off an on several times,but it never hurts to have pics if you're operating without a manual...it behooves me to have'em even with a manual...

 

[waidebe]

Re: 79 25hp 1 spark plug foulling

Good reading! I overhauled carb on 25hp Evinrude. Now runs very well at high speed but very rough at low speed. Both plugs show a lot of oil. Normal with 50:1 fuel mixture?

 

[Al-53]

Re: 79 25hp 1 spark plug foulling

I have A 1983 Johnson 35hp very simular to your engine....when I bought the boat the owner had champions in it and had a spare set of NGK's in the locker box...said he got them at a Marina that did not have champions at the time so gave him these...Any ways

I went on a fishing trip swapped the plugs out to have fresh plugs in after 2 days the boat was running crappy I put the old plugs in and ran like a champ again went to the Marina and got a new set of Champions and the mechanic there told me the OMC motors where designed to run best on the champions


Point being try a set of the champions and see if it makes a difference it did for me

Al