Fouling spark plugs

[WinnerCougar74]

My engine fouls plugs no matter what I do. Are these engines known for fouling plugs? Is there something I can do? Do the ignition boxes get week? 1974 Chrysler 135 hp 135 psi compression. Plugs are correct, timing is correct, new coil, points, plugs and wires. Running recreational fuel at 50-1. Idle screws at 1 turn out on both carbs. I run at low speeds a lot while trying to mark fish.

 

[racerone]

Is there a working thermostat in your motor ?------What plugs are you using.

 

[CaptnKingfisher]

My engine fouls plugs no matter what I do. Are these engines known for fouling plugs? Is there something I can do? Do the ignition boxes get week? 1974 Chrysler 135 hp 135 psi compression. Plugs are correct, timing is correct, new coil, points, plugs and wires. Running recreational fuel at 50-1. Idle screws at 1 turn out on both carbs. I run at low speeds a lot while trying to mark fish.

I set idle screws using an accurate tachometer. Turn screw in til rpms begin to drop due to too lean condition, then turn screw outward gradually. Rpms will begin to climb and as you continue to turn outward they will start to drop again due to too rich condition. Turn screw inward again adjusting for maximum rpms and engine smoothness

 

[WinnerCougar74]

Thermostat is 140 degree and the head runs around 137-142 depending on where I check it. So are you guys telling me you don't have this problem? Champion L20V. Also tried ngk buhw and buhx

 

[tg3690]

Does a short run at higher rpms clear it up?

 

[WinnerCougar74]

It did once but then it just stayed fouled and I had to replace the plugs then it ran great again. Just seems like 2 cycle motors can either be made to idle or run WOT but not both

 

[WinnerCougar74]

I wonder if the people that eliminate their CDI box have better results. It doesn't seem logical but you never now.

 

[racerone]

Nope----When in good condition a 2 stroke will idle all day long !!!------And run full throttle for the next day too !!

 

[WinnerCougar74]

Thank you. Such an important reply. I am glad this can be fixed. I found a factory service manual online that says to start the idle screw adjustment at 1 turn out. Most people say 1 1/2 turns out. If the engine runs good other than fouling plugs, is the most important adjustment the idle screws? They are tricky because it seems like 1/8th turn can make all the difference. I have heard some people say "set it at 1 turn out and forget it". If it won't run right at one turn out then there is something else wrong.

Just to review engine runs well all the way up to 5200rpms with new plugs. It will even idle well for 1-2 hours but eventually the plugs will foul.

This seems to be a hard question to answer but what is the best spark plug for this engine? I tried conventional plugs and almost ruined my engine. They do seem to need to be surface gap.

 

[Sea Rider]

If all is adjusted as per factory specs, 2 stokes motor usually darkens/fouls plugs due to being run for too long at reduced rpm, say trolling rpm where the spark plugs does not reach their Self Cleaning Temp above 500 C. Independently if the plugs fouls, does the motor hesitates, misses when opening the throttle to plane out the combo ? If a motor is used for long time trolling periods must be throttled as if stealing the combo when returning to terra firme, plugs will self clean for next day fishing...

Happy Boating​

 

[WinnerCougar74]

So racerone is wrong. Chrysler 2 stroke outboards can not be tuned to run at trolling speeds all day without fouling the plugs. So this can't be fixed. You have to tune the engine to run at trolling speeds or high speeds. There is no one tune that will consistently do both. I think this is one area where 4 stroke motors shine. They can idle all day and run at WOT.

 

[racerone]

A 2 stroke motor in good condition will idle / troll all day long.----And run full throttle the next day all day long !!!-----I used to troll with a V-6 Johnson 235 HP.----Hours at a time and no sparkplug fouling issues.

 

[Sea Rider]

Just to review engine runs well all the way up to 5200rpms with new plugs. It will even idle well for 1-2 hours but eventually the plugs will foul.

When saying will foul, you mean the electrode will be darkened, carboned up with use ? If so, this is normal, all 2 strokes motors will go that way compared to 4 stroke plugs. When the plugs are fouled, does the motor hesitates, misses a bit when opening fast the throttle past idle rpm right after trolling for long time periods ?

Happy Boating
​

 

[CaptnKingfisher]

Thank you. Such an important reply. I am glad this can be fixed. I found a factory service manual online that says to start the idle screw adjustment at 1 turn out. Most people say 1 1/2 turns out. If the engine runs good other than fouling plugs, is the most important adjustment the idle screws? They are tricky because it seems like 1/8th turn can make all the difference. I have heard some people say "set it at 1 turn out and forget it". If it won't run right at one turn out then there is something else wrong.

Just to review engine runs well all the way up to 5200rpms with new plugs. It will even idle well for 1-2 hours but eventually the plugs will foul.

This seems to be a hard question to answer but what is the best spark plug for this engine? I tried conventional plugs and almost ruined my engine. They do seem to need to be surface gap.

Idle mix is usually the last part of the tune up procedure, if you've got a misadjusted or dirty carburetor and you correct it using the idle mix you're just covering up the underlying issue and it won't perform as good as it should. As far as factory manual recommendation on one to 1.5 turns, I don't personally go by that because the mix is affected by the condition of your carburetor, the type of fuel you use, and the atmospheric pressure.. so say your boating in Denver Colorado at 7000 feet, you probably won't even be able to start the boat with the idle screw set at 1 turn out. But that's just my personal sentiment. I've never had issue with an engine that can only be tuned to idle or full throttle well, I've always been able to get it to do both. That being said engines are not meant to run at idle speed all day long without being opened up. I learned that doing landscaping. Doesn't take long to foul out a chainsaw or a weed whacker by letting it idle too long. Outboards are a little more forgiving but I suspect the same principal would apply

 

[racerone]

A carburetor is nothing but a crude device that responds to airflow through a venturi.----Or wee passage ways in the idle circuit.-----So if motor does not pull proper amount of air through the carburetor you will have issues.----Many motor issues are blamed on fouled plugs.------But the real issues are often neglected.-----Plugs are rarely the issue !!

 

[WinnerCougar74]

I didn't want to offend racerone I just wanted to see if we can figure this out. I wonder what year racerone's johnson V-6 235hp was. Maybe it is a loop charged motor. I wonder if the loop charged outboards are better at not fouling plugs compared to crossflow outboards. This seems hard to pin down. Many 2 stroke engine people like motorcycle and snowmobile users says they can't idle their engines for log periods of time without fouling the plugs. Hopefully this discussion helps.

 

[racerone]

Mine are a pair of crossflow 1982 models V-6 of 235 HP rating.------Will idle hour after hour.-----The fact is that oil / lubrication / fouling sparkplugs are just not well understood on 2 stroke motors !!!

 

[WinnerCougar74]

I have owned this motor for 3 years. The only thing that seems not exactly correct is the compression is lower than factory spec. 137-140 with a good meter. In the 90's with a junk harbor freight meter. I also want to triple check my puddling system. I have read that if it isn't right it can really impact performance and cause inconsistent performance. Also some claim the more expensive 2 stroke oil does not foul the plugs as easily. It would be great to find out if there are any keys to not fouling plugs.

 

[WinnerCougar74]

It seems to me that raceone's johnsons must have been in a tune up sweet spot. It would be great to know what that sweet spot is. What oil did he use? What gas? What regular maintenance? Was everything tuned exactly to factory specs? Were the Johnsons maintained by a professional mechanic or DIY?

 

[dingbat]

Tournament Striper fisherman...... lots and lots of cold water (< 50F) trolling.
My 1997 200 HP Ocean Pro (new power head in 2010) trolls 8-10 hours a day, all day, any day and has never fouled a plug on me.

I run nothing E10 and semi-synthetic oils. Pennzoil Premium Plus, Evinrude XD50 or Merc Premium Plus.