Spark Plugs--conflicting data

[tugboat80]

I have the cleanest, preserved '80's Evinrude 4.5hp ever witnessed. It came with .030 over pistons, new hoses, wires, all parts and lables, paint not a smudge or spec of oil on it. But no model/serial tag. The plug wires show a tag reading of L77J4 or M40FFX. It is a type with kill button on the end of the tiller. I fear that compression is low at 81 and 88 psi one hour after running. My Seloc manual states that '82 and later 4.5 on up hp motors should be gapped at .040. The Seloc book agrees with the Champion L77J4 plugs. This instruction conflicts with data charts found on line showing plug QL86C gapped at .030. I was running the L77J4 at .030 gap suffering multi pulls to start, and eratic idling. Today I sprayed some DeepCreep into the cylindars, carb, and ran a gallon of non ethanol premium with XD30 and 2 oz of SeaFoam arround tha lake with plugs gapped at .040. There was miniscule signs of carbon in the motor but I did it any way to try to raise compression. I gained one pull starting, SMOOTH idling, easy transition throughout all rpm changes and an all round more pleasant hum of a sound. But no gain in compression. Question: What does a guy do with conflicting specification data? Is the compression I am having normal? This motor will push my 12' rivited tin at 10 mph with my tiller extention balancing the load.

 

[Haffiman]

Re: Spark Plugs--conflicting data

The QL 86C is a hotter plug. Might improve idling and cold start, but may be a bit too hot if running full speed. Your engine has no thermostat and depending on weather/water temp use what gives you the best result. Perhaps the 86 plug in winter and the 77 in summer?? It has been a lot of changes in the recommendations over the years different from what originally stated from factory. This is mainly based on user experience and not the testing during factory conditions that might be a bit different.

 

[JB]

Re: Spark Plugs--conflicting data

Ahoy, tugboat.

Welcome to iboats.

First: there is nothing wrong with your compression. You have a rope start outboard. The important thing about compression tests in 2 strokes is that all cylinders fit in a 10% window.

Psi specs are very important in 4 strokes, much less important in 2 strokes. 2 Strokes don't have valves to worry about.

Champion L77J4 is the correct plug. You may gap them at .030" for general use or .040" for trolling. There are charts on the net that really screw up plug assignment. Believe OMC.

That is a great little engine, descended from the best outboards ever made. Love her and she will love you right back.

 

[seahorse5]

Re: Spark Plugs--conflicting data

In the mid 1990's the then OMC and Champion Sparkplugs reviewed and changed a lot of the plug recommendations so older literature may be obsolete.

The official factory chart shows the 4.5hp from 1980 to 1985 should use the Champion QL86C gapped to .030". Install that plug then tell us how the motor runs. I'll bet your motor now runs better due to the decarbonizing you did with the Deep Creep and not so much from changing the plugs.

 

[nwcove]

Re: Spark Plugs--conflicting data

i would be curious to know why the motor is bored out 030. sounds like a 100/1 deal that went wrong. but plugs can make a noticable difference.

 

[tugboat80]

100/1 ???

100/1 ???

Observing the showroom condition of the motor overall, I wonder if the first owner tried running it with no lube?; but the bolts show no evidence of tool marks anywhere. Perhaps a disaster happened in assembly at the factory so they boored over to hide the mistake. What is meant by 100/1?

 

[Haffiman]

Re: 100/1 ???

Re: 100/1 ???

The 1/100 was a mistake by OMC when it came to oil-mix. Stay with 50:1!!!!

 

[boobie]

Re: 100/1 ???

Re: 100/1 ???

The mtr would run on 100:1 okay but the probs arose when the mtrs were left sitting without fogging.

 

[1946Zephyr]

Re: 100/1 ???

Re: 100/1 ???

In the mid '80's, OMC decided to build their motors to be "100:1 motors" but quickly ended up paying for that mistake. A lot of owners had their powerheads rebuilt, or replaced, at the cost of the manufacturer. I actually had a 1986 25hp given to me, which was a benefit to this recall.

 

[tugboat80]

Re: Spark Plugs--conflicting data

I havent got to the Ql86c as suggested. I let the 4.5 set some two weeks, then tank tested the l77JC4 gapped at .035. She would not start, would not start. I spark tested with a piece of baling wire from lead to ring around the spark plug, got spark jumps on both. I looked inside the cylinder holes, regapped to .040, wet the tips with fuel, replaced, and she started first pull or the cord. This engine likes L77JC4 gapped at .040. QUESTION: Will miss recomended plug specifics or larger than recomended gaps damage an engine?

 

[JB]

Re: Spark Plugs--conflicting data

Those engines ran very well on the L77JC4 before OMC and Champion concocted that chart (that is world infamous for bad recommendations). You may have run into one of the errors.

I would expect it to run well at cruising speed with L77JC4 gapped at .030" and have no explanation why she wouldn't start.

I think you should try the QL86C to support or contradict the recommendations above. JB Does not know everything all the time.