1984 Johnson 8 hp J8RCRM spark plug gap

[Steelhand]

what do I set the gap on my 1984 8 hp Johnson at? I pulled the plugs to check them and dropped one right on the gap. Now one is set at 030 and the other is 035. I walked away for a week, now I forgot which one is which. What is the right one please?

 

[Vic.S]

0.030" is the currently recommended gap.

Originally it was 0.040" but at sometime OMC changed the recommendation . I believe to extend plug life but would not bet on that as the correct reason.


The recommended plugs are Champion QL77JC4. These are inductively suppressed. Do not be tempted to use resistor suppressed plugs.such as NGK BR7HS-10 which are often listed and sold as equivalents.

If you live where Champiom plugs are difficult to get use NGK BZ7HS-10

 

[Steelhand]

Thanks so much Rear Admiral. While i'm at it, I have a 79 6hp Johnson Seahorse that has a lable on one of the spark plug wires reading Champion L78V That's what I have in it. Would they do any harm in the 84 8 hp? Also, what would happen if I would have stuck them both back at 035?

Sorry for stupid questions but you should see the look I get when I ask my grandkids. LOL

 

[Joe Reeves]

In agreement with Vic....................

As Vic States.... Plugs should be CHampion QL77JC4 spark plugs... OR.... the plain Champion L77JC4 spark plugs if you are NOT using any electronic equipment. The "Q" designation indicates a "Suppressor" to help quiet electronic noise in such type equipment.

You can use either setting.... .030 for long life.... or.... .040 for a super strong spark. There is no middle of the road, so to speak, recommended.

 

[Steelhand]

Oh, I just checked what is in the 84 8hp motor. They're NGK 7HS-10

 

[Steelhand]

Thank you J Reeves, since you second the motion, I'll get the right stuff and have them on hand.

 

[Vic.S]

Thanks so much Rear Admiral. While i'm at it, I have a 79 6hp Johnson Seahorse that has a lable on one of the spark plug wires reading Champion L78V That's what I have in it. Would they do any harm in the 84 8 hp? Also, what would happen if I would have stuck them both back at 035?

Sorry for stupid questions but you should see the look I get when I ask my grandkids. LOL

L78V are surface gap plugs They were, I think, the plugs originally fitted in that engine but they are no longer the preferred choice. The hand book for my engine lists them as alternatives for sustained high speed operation.
Currenty QL77JC4,, or as Joe points out the unsuppressed L77JC4,, or alternatively QL86C (or L86C) are the current recommendations

As Joe says You can set the plug gaps to 0.030" or 0.040" whichever seems to work better( or anywhere in between for that matter) but you are unlikely to notice any difference..... I didn't when iI re-gapped mine from 040 to 030

Oh, I just checked what is in the 84 8hp motor. They're NGK 7HS-10

They are the equivalent of the un-suppressed L77JC4 and will work just fine. I have a set as well as the original Champions
Most of the world outside the USA much prefers NGK plugs over Champions
(-10 at the end of the number indicates that they are supplied ready gapped at 0.10mm )