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I have a 1967 100 hp outboard only has the electronic ignition removed.........

B

Badbear 45/70

Member
I have a 1967 100 hp outboard only has the electronic ignition removed and is replaced with the older battery, points and coil ignition. With the electronic ignition it says to run L77JC4 but what plug should I run with the standard ignition. I have L82C plugs in it now and it runs fine but if there is a better plug to run then that is what I want.
 
L82C are often listed as an alternative to L77JC4 but are a little hotter

1966 100 hp had coil and points ignition and used JC4 but JC4 is only 3/8" reach compared with L77JC4 and L82C which are 1/2"

Assuming the engine is genuinely a 1967 model I'd go with L77JC4, or L82C if there are any signs that a hotter plug is needed

( If you put the 1/2" reach plugs in a 1966 model instead of the 3/8" ones the pistons might hit the plugs , but I guess that is not happening)
 
Agreed, Vic. The 67 should have adequate clearance since the spark plug/head threads are 1/2". The 66 is 3/8" so interference with the 1/2" plug and especially the non surface gap type is possible, depending where it ends up when tightened.
 
I have had no problems with the L82C plugs I have in it now and that is with a 6000 rpm rev limit because the good prop I had got stolen off my old hydroplane. I just need a plug recommendation for a regular plug for the beast. Oh and having raced a Merc 1500XS for years I am aware of the L76V plugs ad they are not good of a non- electronic ignition.
 
You use a Dremel tool and split half of the electrode leading edge and spread into a "V". The more a electrode is exposed to the air/fuel mix the easier it is to ignite.The only draw back is the ignition system/battery voltage has to top notch. You have to have a hot spark at a certain dwell time to light off the mix, all controlled by points cam lobe.
 
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