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1976 4 HP Evinrude

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professor229

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Hi.... I have owned a 4 HP Evinrude for my 12 foot Lund for five years now. I haven't used it all that much because I also use a 6 HP motor on the boat more often, but this year I have used the 4 quite often and it has gotten quirky on me.... Now, I always use new gas, know how to adjust the high speed needle, and take care of my motors. I was a golf course supt. for over 30 years so I know a lot about small engines BUT not boat motor engines other than the basics... and this one is quirky enough to where the answer might be obvious to a member of this forum... here's hoping someone will recognize the problem....

First, when I am done with all small engines, I shut off the fuel lines and have done that for over 30 years.... with a shut off valve. On the Evinrude boat motors I simply disconnect the fuel line at the motor, and let the remainder of the fuel in the internal fuel line and carb get used up so the engine then dies..... a seemingly minor fact but it does enter in on this .... please bear with me....

The problem... The motor starts on the second pull almost all the time.... with a little cloud of blue smoke.... then we are off across the lake... and almost immediately the symptoms appear.... there is the typical goofiness for about five seconds as the motor warms up a bit but then we can go full throttle with it... and it will run fine for about a two second count.... then it will hesitate/bog down for a split second, recover, and run fine for another two seconds perfectly and then hesitate for a split second and bog down a bit... and then repeat.. over and over... constantly. Yes, I have the cap off the tank to make sure there is no pressure in the tank.... and gas can be sucked into the motor....

Now, here is where it gets goofy..... As the engine does this two seconds fine/ split second hesitating across the lake, I near my destination so I disconnect the fuel line at the motor...... so I can run the internal gas line out of gas as well as the carb.... The motor will run on this "internal" gas for about 20-30 seconds before there is no gas left... The first few seconds after disconnecting the gas line.... the motor runs flawlessly with no hesitation what so ever... and I mean perfectly until the gas is gone...... I suspect it has something to do with whatever the motor part is called that sucks the gas???? and maybe there is more "air " because the gas line is disconnected?

I am a pro with golf course equipment motors.... but boat motors? Not so much.... so I need to ask why it runs so well when I disconnect the gas line....

Any help? Any/ all suggestions welcome and appreciated....

Thanks... Dennis
 
Hey... one of the first interventions I tried and yes, both spark plugs fire fine. I did contact an "expert" who rebuilds these as well as posting on this forum and he got back to me with his best guess.... and it makes sense... As he stated

"Given your description my first guess is a carb issue and probably a bad float.
This can be common with the older motors especially if they have a wood float.
In particular the wood floats tend to deteriorate over time and eventually absorb fuel
which prevents the float from floating (rising) high enough to push the needle to close
off the fuel flow. Motor will start but bog out as the carb floods. When you disconnect the
fuel hose the fuel pump will soon stop pushing additional fuel and stop flooding the carb.
Once the flooding stops the motor will run until it empties the carb, probably runs for 1-2 minutes,
eventually surges just before it quits. "
 
First, the engine has a fixed high speed jet (No knob). So if you are thinking you are adjusting a high speed jet (as you mentioned), you are adjusting the low speed jet, which you may have set too lean as you come off of full throttle it begins to backfire and spit.
 
I see an adjustable high speed mixture needle.----But do a complete evaluation of this 45 year old motor.---Good luck with it.
 
racerone said:
I see an adjustable high speed mixture needle.----But do a complete evaluation of this 45 year old motor.---Good luck with it.
Click to expand...
Yes, it has both a high and low speed needle..... and adjustment.... I have adjusted the high speed wide open several times and this is a no brainer for adjusting..... have done it 100s of times... but it doesn't matter where you adjust it... and you can get it to drop off and then back it out but the symptoms are there no matter what you do.... This motor runs good enough to finish out this summer but I have so many other projects now that this will wait until it gets colder..... winter... whatever... I just bought a vintage Alumacraft boat to restore this morning.... and have a choice of starting that today, or mowing the lawn... guess which one is going to get done?
 
I am 99% sure that the electrical components of this motor are fine. I have tested that part of it as one of the first interventions. The one telling variable that is undeniable is when you disconnect the gas line to let the motor run out of gas which has been part of my regimen over the years and for that 30 seconds before the internal gas line and float bowl run dry, the problem disappears and the engine runs flawlessly until if finally runs out of fuel. It has to be something fuel related. I contemplated that there might be a problem with my three gallon tank or the hose connection etc..... but I use this tank on my 6 HP Evinrude as well and it runs perfect with it. So you can eliminate the gas tank and line as the problem. I need to spend some quality time with google today and find a video showing how to replace that float. I have never had a float bowl off a marine carb but cannot imagine that it is that difficult other than the fact that you are working in a confined space. Then there is the question of finding a replacement float and the proper setting. I think this is where I should start.
 
There is a quality factory carburetor kit.-----Covers many years and motors from 1.5 HP to 20 HP.-----All the same and simple.
 
Gave up.... took it to the best OMC mechanic in MN yesterday morning and got a call in the afternoon... he said the carb needed rebuilding (kit) as the needle was struggling as well as the float... his procedure is then to run it in a tank for 15 minutes to make sure... it didn't make it to the 15 minute deadline and stopped running... did a fuel pump test and it failed... new fuel pump installed and it ran the 15 minute trial perfectly..... I will pick ip up today, $160 lighter but honestly, he earned his money.... Just an FYI....
 
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