spark flug fouling

davejnz

Petty Officer 2nd Class
Joined
May 2, 2004
Messages
115
I own an 87 Johnson 20hp,Just rebuilt the carbs,set the low-speed needle 1 turn out from lightly seated,ran fine all day,after idling back to dock for a while,it stalled and was hard to get started.I got home and checked out the plugs(L78V).They both were healvily coated with carbon and were shiny like they were wet.My manual calls for QL77JC4.Do you think i should replace the old-ones with the JC4's or put the L78V's back in there?
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: spark flug fouling

Use the L77J4C, Dave. Gap them at .040"<br /><br />If you still experience fouling, switch to L77J6C gapped at .040".<br /><br />Good luck. :)
 

davejnz

Petty Officer 2nd Class
Joined
May 2, 2004
Messages
115
Re: spark flug fouling

thanks,I'm having trouble finding the L77J4C around here.The QL77JC4 seems availiable everywhere.Is that a special order plug?
 

DHPMARINE

Captain
Joined
Dec 16, 2003
Messages
3,688
Re: spark flug fouling

At my shop we stopped stocking L77JC4's as they are the same as QL77JC4's,just not resistor plugs VRO systems call for.Slightly more $$$ than non-resistor,but they seem to run okay.Will have to look into the L77JC6's.Didn't realize they existed.Good food for thought.<br />Seems if you have to run a hotter plug than listed,there may be other things going on,like poor spark,over oiling,etc.<br />DHP
 

davejnz

Petty Officer 2nd Class
Joined
May 2, 2004
Messages
115
Re: spark flug fouling

Well,I did a decarb on motor with old plugs,ran it in a tub,took over an hour for that little 20 <br />to burn up a gallon/seafoam can mix.Took the boat out on the ICW and ran it WO to blow all that excess crud out,took it on to a bank,installed th new(QL77JC4)plugs and tore down the river all afternoon,stopped and idled for 30 min and adjusted the low-speed idle and it is idling perfect.just wanted to thank all you guys for all the wonderful advice you've given me(clean carbs,decarb,plugs,etc..) Next step will be to get her propped right after my tiny tach arrives
 
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