Lean/Rich knob

[viciousfishes]

Hey yall,

I was wondering.. what is the rich/lean knob reffering to on my 68 20 hp johnson? Is it oil and fuel or air and fuel? Im trying to figure out what it does, if I play with the knob while its running it doesnt seem to make any difference? Is that bad?

Thanks!

Bradley

 

[bigmoe]

Re: Lean/Rich knob

All 3 since the oil is mixed in the gas. Its the air to fuel ratio adjustment on the slow speed circut. You might not notice it when you play with it but if your carb is adjusted correctly it could foul your plugs when you richen the mixture. Mine does. I believe its for when you travel to higher altitudes.

 

[lindy46]

Re: Lean/Rich knob

It's for adjusting the slow speed/trolling of the motor. That needle should be open about 1.5 turns and you should notice a difference when you adjust it. Turn it clockwise (lean) too far and you'll get a sneeze. Then open it (counterclockwise) about 1/8 to 1/4 turn to optimize. If it's not making any difference, it may be time for a carb cleaning/rebuild.

 

[kfa4303]

Re: Lean/Rich knob

I agree with lindy46. It should make a difference as you twist the knob. If it's not, then you probably need a carb rebuild, which is super easy on these vintage Johnsons. The kits are about $20-$25 and contain all new gaskets and seals for your carb. You can even get it here from iboats. Also, get a can or aerosol carb cleaner too. After you've rebuilt your carb, the rpms should go up as you turn the needle in and should drop as you twist the needle out. You only need very sloght adjustments in the needle to make a difference. make a 1/8 turn then wait 10 sec or so for the motor to respond then adjust again until desired rpm range and idle are set. Here's a couple links on how to clean and rebuild a carb. Good luck.

http://www.outboard-boat-motor-repa...hnson 5.5 HP 1954-1964 Carburetor Tune-UP.htm
http://www.sschapterpsa.com/ramblings/johnson_QD.htm
http://forums.iboats.com/showthread.php?t=167352
http://www.youtube.com/user/PistonPumper -------------- start around episode 19.

These links aren't specific to your motor per se, but all these old Johnson carbs are basically the same. Great little motor you got there. Well worth the effort to get and keep her running. Good luck. Keep us posted.