How much should '60's motors smoke?

Joined
Jul 10, 2003
Messages
9
I've fired up a few '60's outboards lately and they seem to smoke badly. Don't know whether the motors are bad or just standard for an age where pollution control meant that oil and car companies were trying to control Ralph Nader. <br /><br />I suspect part of my problem is that I'm running them in small tanks on test so that there is huge cavitation and a relatively tiny amount of water in which to disperse the exhaust. A moving boat would be dispersing the same amount of smoke into a vastly larger volume of water while moving through it, which might spread it out a lot more and make it less obvious.<br /><br />Anybody got any simple tests for working out how much is too much smoke on a tank, or any other, test?<br /><br />I'm wondering what is the normal amount, and type (colour,density etc) of smoke to expect?
 

JasonJ

Rear Admiral
Joined
Aug 20, 2001
Messages
4,163
Re: How much should '60's motors smoke?

If you are running the proper mix ratio, there is nothing that can be done about it. I have a 1970 125 horse Merc, and it smokes like crazy out of the water, but there is little smoke when it is in the water.
 

paulgp6022

Petty Officer 1st Class
Joined
Jul 27, 2002
Messages
288
Re: How much should '60's motors smoke?

Funny this should come up. I was running my '03 Merc 75 with less than 10 hours on it in a tub of water so it was quieter than the muffs. There is this exharst relief port of sorts right below the cowl. Well let me tell you, the smoke that was billowing out of it was like a smoke cloud from hell. I thought my new motor was screwed up.<br /><br />I then took the tub away and put the muffs on the intake like I usually do, and viola, no more smoke from the relief port. I think the small area in the tub was causing some sort of negative exhaust pressure and shooting it back up the hub and through that relief port. Needless to say I wont be running it in the tub anymore!
 
Joined
Jul 10, 2003
Messages
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Re: How much should '60's motors smoke?

Bump.<br /><br />In light of JasonJ and SS Minnow's replies, does anyone know if the smoke on a tank test is going to be a lot worse than at sea, or just idling at the dock? If so, why?<br /><br />The problem that worried me was dense white smoke turning brownish as throttle opened in a tank. We're only talking maybe a third throttle at best. First on the 1967 60hp V4 Evinrude, then on the 1964 7.5hp twin Mc Culloch. <br /><br />It's not water in the cyls. <br /><br />I was thinking it's unburnt fuel coming out the exhaust, but SS Minnow's reply suggests it might be recirculating exhaust smoke getting denser as the throttle opens. It obviously can't be sucked back in the intake manifold as there's not enough smoke up there, but maybe if it was being sucked in the water intake and spewed back into the exhaust housing and coming out the exhaust again it would make sense. <br /><br />Anybody know for sure? Or just got an opinion?
 

Lark40

Senior Chief Petty Officer
Joined
Oct 29, 2001
Messages
793
Re: How much should '60's motors smoke?

My 1960 Lark smokes up the tank and the docks alike. That's because pre-1964 Johnson/Evinrudes used a 24:1 gas/oil mixture. <br /><br />Also, I just bought a 2004 Johnson 30 hp (old technology 2 stroke) and ran 25:1 mix for the break-in period and it also smoked up the docks.<br /><br />My new engine gets almost three times the mileage of the old one. Part of that is probably due to improvement in burning more of the gas instead of passing it out the exhaust.<br /><br />The smoke is just intrinsic to the "classic" technology. That's why these carbed two-stroke engines can't be sold after 2005.
 

Bco128

Petty Officer 1st Class
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Jul 6, 2003
Messages
220
Re: How much should '60's motors smoke?

i asked my uncle about this and here is his reply. " If the smoke is so thick you can't see through it....then thats just about right"
 
Joined
Jul 10, 2003
Messages
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Re: How much should '60's motors smoke?

Don't know anything about motor bikes, but why don't big capacity motor bikes from the same era smoke up as much?<br /><br />Or lawn mowers. Even allowing that my big Evinrude is about 7 to 14 times the capacity of 160cc down to 80cc mowers of the era, you'd still die of smoke poisoning before mowing half your lawn if they put out as much smoke per cc/ci.<br /><br />Is there any difference between two stroke oils that explains any of it?
 

alcan

Commander
Joined
Dec 14, 2001
Messages
2,505
Re: How much should '60's motors smoke?

Hi Tinker<br />First of all it's hard to say how much smoke you have or have not sitting here. Any two-stroke motor smokes, and should. Smoke is a good thing. Most outboard motors exhaust out the lower leg, under water. When the boat is under way there is a vacuume formed under water behind the lower unit. This helps suck exhaust from the motor and muffles the noise. When the boat is not moving,(at the dock or test tank) the water is basicly plugging off the exhaust pipe (like stuffing a potato in your car exhaust). This is why an exhaust relief port is provided (an opening above the water line and out the bottom.Agian when the boat it moving the vacuume created sucks most of the gas past the relief port . When testing in a tank there is no where for the exhast to go. And since most folks use trash cans or barrels there is not enough water for to create this vacuume affect, if there was it still wouldn't matter, your not going anywhere and neither is the smoke. Shops use tanks that are equipt with fans that draw off most of the exhaust and pipe it outside. If you are working on/adjusting and motor and have no breeze, set up a small fan so your work area is more comfortable. This is also a prudent idea when tuning air cooled motor cycles 2 or 4 stroke (helps cool the motor). Now you can have too much smoke. More often than not this is due more to an over rich air/fuel mixture (carb out of adjustment) rather than too much oil. Of course more oil more smoke. Lets say the your motor is supose to run 50:1. I you doubled the oil to 25:1 you would not notice twice as much smoke. This assumes the motor is properly adjusted in the first place. Do not adjust a motor so lean it dosen't smoke a little. Smoke is your freind. When you start an outboard cold, you choke/prime it. This procedure draws a super rich fuel mix into the engine. The engine has no fuel in it, it is how ever full of air. When all this air and super rich fuel get all mixed up in there and lit off, your going to have more smoke for a few miniutes, it doesn't matter how new or old your 2-motor is. Smoke is part of motor language. It is one way your motor has to talk to you. Get to know you engines and talk back to them once in a while. Be nice to them.
 
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