1973 outboard rough at all speeds

[jl_photo]

1973 40

starts easily every time. usually don't need choke

a little smoky may be rich.

runs rough at all speeds.

what oil mix ratio does this motor use?

thanks

 

[bassboy1]

Re: 1973 outboard rough at all speeds

50:1. That is a half a quart of oil for 6 gallons of gas.

 

[jtexas]

Re: 1973 outboard rough at all speeds

back to basics:
Compression test.
Spark test.
Inspect fuel lines, replace any that show signs of aging.
Make sure fuel is fresh and clean.
Fuel line holds pressure?
Fuel tank vent clear?
Time since last carb rebuild?
Completed any maintenance recently?

 

[jl_photo]

Re: 1973 outboard rough at all speeds

back to basics:



Compression test. 150#


Spark test. good on lower ok on upper


Inspect fuel lines, replace any that show signs of aging. fuel lines ok


Make sure fuel is fresh and clean. fuel ok


Fuel line holds pressure? yes

Fuel tank vent clear? yes


Time since last carb rebuild? probably a long time. I cleaned the bowl, jet idle jet and needle & seat. looked ok


Completed any maintenance recently? just bought the motor history unknown

is it likely to be timing or carb?

I think its running rich, i accidentally ran it out of gas. when I checked the plugs they were wet. I need to get some more gas and run it and turn it off normally and re-check the plugs.

 

[jtexas]

Re: 1973 outboard rough at all speeds

that's 150 on both cyl? outstanding!

spark "ok" on #1 - does it jump a 7/16" gap with a strong blue spark? If not, swap the coils, see if the problem follows the coil. if so, replace the coil, if not could be powerpack but I'd troubleshoot the fuel system before spending that much:

checking the condition of the spark plugs after running - good idea.

in the "Engine FAQ" section of iboats is a thread called "carb needle adjustments" or something like that - its about adjusting your mixture screws - see if that helps.

try pumping the primer bulb while its running rough - if that makes it smooth out, rebuild the fuel pump.

you could try spraying some fuel premix into the carb throats while its running (sorry, is that one carb or two on that motor?) - if it smooths out, that would pretty much indicate a carb rebuild is in order - soak 'em overnight, blow out the passages, etc.

you might've already did this - with the unknown history, might want to put in a water pump kit - impeller ought to be done every couple years or so as preventive measure.

 

[lexkyboater]

Re: 1973 outboard rough at all speeds

Another thing, after adjusting idle speed mixture, if that doesn't fix the problem, is to try is to turn the rich/lean mixture in toward lean as you're running to see if that clears it up. My 71 Johnson 9.5 HP was running like it was bogging or you might say rough, and when I turned the idle mixture knob in at WOT, it took off! This was after I adjusted the idle speed mixture according to Joe Reeves' suggestion. My main jet may be a little rich or someone could have reamed it out (honest, it wasn't me). Also, it sounds rich, but you might want to try pulling the choke as you take off to make sure that makes it run worse, to verify a rich mix. If you're compression's good and you're smoking a lot, that does sound like a rich mixture, but just make sure.

Keep in mind that that idle speed mixture affects how it runs at both idle and WOT. Only the high speed jet affects how it runs at higher speeds/throttle openings, which is why you always want to get it idling right first before trouble-shooting other areas of the throttle openings. See attached carb range pic I modified from a dirt bike site.

 

[jl_photo]

Re: 1973 outboard rough at all speeds

my johnson dealer helped me discover that I had "cleaned off " a small gasket between the main jet and the bottom of the bowl. I had thought is was just crud.

carb kit in hand. I will install it in the morning.

thanks for your help.

 

[spy1309]

Re: 1973 outboard rough at all speeds

On my original Johnson 6 gal gas tank whitch came with the 1960 40hp Johnson says to mix one third of a pint per gallon in a 50:1 ratio.
Now 3 thirds is one pint per 3 gal of gas , 6 gal 2 pints, 2 pints = one quart so how come he has to use half a quart of oil per 6 gallons.
Did Johnson the manufacurer of the engine lacked the math skills?Or mislead the customers?

 

[jtexas]

Re: 1973 outboard rough at all speeds

On my original Johnson 6 gal gas tank whitch came with the 1960 40hp Johnson says to mix one third of a pint per gallon in a 50:1 ratio.
Now 3 thirds is one pint per 3 gal of gas , 6 gal 2 pints, 2 pints = one quart so how come he has to use half a quart of oil per 6 gallons.
Did Johnson the manufacurer of the engine lacked the math skills?Or mislead the customers?

early-60's OMC was recommending 25:1

 

[spy1309]

Re: 1973 outboard rough at all speeds

Well the writing on the original 1960 tank clearly states 50:1 ratio, one third of a pint per gallon nowhere to be found 25:1 on the tank.
So no matter what year the formula remains the same 50:1 for 6 gallons = 1 quart = 2 pints

 

[jtexas]

Re: 1973 outboard rough at all speeds

Well the writing on the original 1960 tank clearly states 50:1 ratio, one third of a pint per gallon nowhere to be found 25:1 on the tank.
So no matter what year the formula remains the same 50:1 for 6 gallons = 1 quart = 2 pints

sorry, must have misread you before;
1 gallon = 128 oz.
128 ? 50 = 2.56 oz, about 1/3 cup (8 ? 3 = 2.67).
therefore, 50:1 is 1/3 cup per gallon, 1 cup per three gallons, 2 cups (1 pint) per six gallons.

1/3 pint per gallon is 25:1.

"one third of a pint per gallon in a 50:1 ratio" - clearly, Johnson lacked math skills.

 

[spy1309]

Re: 1973 outboard rough at all speeds

LOL so I am running double the oil quantity I should no wonder I smoke like crazy lol.
Well more oil is better than less oil but this 1960 engine of mine runned all his life 1 quart per 6 gal, even the original owner told me that is the amount he mixed, so far the engine lasted 47 years pretty decent I l say.
Next tank will be half a quart per 6 gal hope I will not be sorry.

 

[jtexas]

Re: 1973 outboard rough at all speeds

I'm not saying 50:1 is right for your engine..........I'm just saying 50:1 is one pint per six gallons.........can't account for the discrepancy in the writing on the tank..........absent any reliable advice to the contrary, I would have supposed 25:1 is mo better in your case.........hope I haven't added to your confusion - doesn't seem like I helped ya much -