HI All ! I'm a virgin with some Questions...

WATERTIMES

Seaman
Joined
Jun 13, 2008
Messages
67
I just purchased a {I'm guessing}1975 Johnson 4H.P outboard last evening.I need to know exactly what I've got model#4w75a serial#c19963.
I had the man show me it run,runs very good except when at slow idle speed it will hiccup and then die out,other than that it runs very well.I'd like to know
if this {now that I purchased it} is a reliable motor?The man used it on his 15ft.fiberglass rowboat and said it was not enough to power him with other people on his boat, but did well with him alone,lifting his bow the whole time.
He said for what I have it would be way better for.I'm using it on a 1978 starcraft jonboat 14ft.aluminum.He had wanted $200.00 for it which I felt was pretty cheap,but after getting to his house was a long,long maze of nothing but miles and miles. I got him down to $100.00 with the tank.The motor looks very well kept,runs good other than the hiccup in slow speed.Did I get a great deal or did I get a fair deal? I need info from someone on how to use the rich/lean knobs on the front of the motor I need to understand how they work.If anyone can help I would appreciate it greatly,before I go burning up the motor. I'll have more questions later on as I go. Thank you all!!
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,226
Re: HI All ! I'm a virgin with some Questions...

The hiccup at idle is called a "lean sneeze", and is caused by the fuel/air ratio being too lean--that is not enough gas for the amount of air. It is simple to fix. Just give the slow speed knob a tweak toward the left (rich). That is what it is there for.

There is no mystery about those knobs, and they won't blow up or bite. To oversimplify, they act like water faucets, controlling gasoline instead of water. Opening them toward the left increases the flow, closing them decreases the flow. The fuel/air ratio has to be within a certain narrow range for any engine to run.

So, what to do? They are already close or you wouldn't be able to get it started and keep running. To fine tune them, run the motor on a boat, in the water, at full throttle and turn the lower (high speed) knob slowly to the right till the motor starts to falter, then turn it back to the left till it regains power. To far left will make it "four-cycle" or fire every every other stroke and again lose power.

Then slow down to idle and do the same with the upper (slow speed) knob. You already know what that one needs...turn it toward rich because it is lean sneezing.

After they are correctly adjusted, you can pull the knobs off and reinstall them at mid-scale without disturbing the adjustment so you know where they should be in the future. Then, more or less forget them.
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: HI All ! I'm a virgin with some Questions...

exactly. it will get you to the fishing hole, just not fast. welcome to iboats.
 

WATERTIMES

Seaman
Joined
Jun 13, 2008
Messages
67
Re: HI All ! I'm a virgin with some Questions...

Thank you guys for the help in understanding how the knobs work,it doesn't seem too complicated.Do you know what year motor that is by the model & serial #'s I gave? Also is it a good reliable motor to own? How about the deal I got for that type & make of motor? Thank you again!
 

WATERTIMES

Seaman
Joined
Jun 13, 2008
Messages
67
Re: HI All ! I'm a virgin with some Questions...

I forgot to ask ...what would be the proper fuel mix for this type of motor? The man I had gotten it from said he was using 16oz to a gallon of gas?.Guidence very helpful!
 

tashasdaddy

Honorary Moderator Emeritus
Joined
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