91' 40 hp johnson spark plug ?

[airshot]

Here in NW Ohio we are thinking of the upcomming boating season and the question I am asking is..on my 40 hp (VRO) changed over to direct mix 50-1 motor I found I have been fouling spark plugs. I had to replace them three times over last summer. The motor runs great otherwise, excellent compression and very good spark. Is it the premix fuel that is causing the problem and would going to a hotter plug be a wise solution? The fouling occurs at start up an low speed running. Carbs have been rebuilt and motor idles very well with newer plugs. I do have a fairly long fast idle run to get to the lake before I can open it up. Thanks in advance for all the great help that I have recieved on this forum.

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[ezeke]

Re: 91' 40 hp johnson spark plug ?

QL78YC at .030 is the correct plug for the recreational models.

Among reasons for fouled plugs are:

Failed thermostats;

Overpropped, resulting in lugging the engine;

TC-W3 oil other than synthetic TC-W3 or synthetic blend TC-W3;

Failing to perform annual de-carbon treatment as recommended;

Failing to mix Carbon Guard or Ring Free or similar in the fuel regularly.

It's generally not necessary to replace plugs when carbon fouled; a lttle carb cleaner and brushing will usually spruce them back up.

 

[airshot]

Re: 91' 40 hp johnson spark plug ?

Thanks for your reply, I do use pennzoil tcw3 syn blend oil, used it forever without a problem. My plugs are not carbon fouled but fuel fouled. It is rare to see much black on my plugs but when they foul out they are wet with fuel.
When I put in a new set the motor runs perfect for about 6-8 outings then starting difficulties start showing up, replace the plugs and perfect running motor again. I have checked plugs after 3-4 outings and they appear great just a brown coloring, no black, no excess fuel. When the starting problems begin, it is after the engine has been run a while, not a cold start. Actually the engine start very well when cold. If we run out to fishing grounds 45-60 minute run, then sit for a couple hours that is when I begin to see starting problems. Thanks again for your suggestions.

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[tashasdaddy]

Re: 91' 40 hp johnson spark plug ?

what is your warm starting procedure? using old fuel, will do that. with ethanol in the fuel today. adding new fuel to old fuel just makes more old fuel, run you tanks as low as possible, then wait to fill, until going out.

 

[airshot]

Re: 91' 40 hp johnson spark plug ?

Thanks again for the reply, I drain the tank at the end of the year and drain fuel line as well. Start season with fresh fuel, add Sea Foam, and typically add 4-6 gal of fresh premix each time I go out which is at least twice a month if not more. The motor has very low hours and a visual look inside each cyl shows no carbon buildup, you could almost eat off the piston tops.
I know the VRO system leans the oil down at low speed and richens it at high speed, I was thinking the 50 to 1 premix at low speed may be causing the fouling. My warm starting proceedure is to move the fast idle arm up a little and start, if it does not fire after a few revolutions, then start again with more fast idle and mabey some choke depending on how long I have sat.

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[ezeke]

Re: 91' 40 hp johnson spark plug ?

Tan color on the plugs is normal - what they should be after running a while.

A lot of fishermen use a gap as wide as .040 if they troll a lot.

 

[airshot]

Re: 91' 40 hp johnson spark plug ?

That may be an idea, while I do not do a lot of trolling, I do have a long ride to and from the lake from where I launch,that is a fast idle only ride. I might try opening the gap a little at a time and see what happens. thanks for the suggestion.

Airshot