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Catalina/Capri 25/250 Sailor's Forums

General Sailing Forum

How much smoke is normal from a two stroke engine?

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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Initially Posted - 09/17/2007 : 13:48:13

We've got a '97 Johnson Sailmaster 8hp two stroke on SL. I notice that it smokes constantly as it's running. The fuel-oil mixture is 40:1 which is correct for the engine, and it smokes less after it warms up, but never completely goes away. It's not like I'm laying down a smoke screen or anything, but it's constant light smoke, enough to notice, and enough to irritate me. I don't recall the Mercury 7.5 I have on my San Juan 21 smoking constantly like this, but admittedly I rarely ran it for more than about 10-15 minutes at a time. I only used it to get in and out of the marina whereas we use the Johnson fairly frequently to motor miles & miles out on Puget Sound.

David
C-250 Mainsheet Editor

Sirius Lepak
1997 C-250 WK TR #271 --Seattle area Port Captain --

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Sloop Smitten
Master Marine Consultant

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USA
1181 Posts

Response Posted - 09/17/2007 : 14:47:12

David,
I looked around online but could find no information on the 97 Salimaster oil/fuel ratio's. What I did find was almost all modern (90 and up) Johnson's use a 50:1 ratio after they are broke in. (25:1 during break-in) Given the way a 2 cycle engine dispenses its oil/gas mix directly into the crankcase I would think you are providing too much oil if it is smoking. I would back off to 50:1 in that case. Where did you get the 40:1 ratio from? Circa 1950 Johnson's used a 35:1 mixture so 40:1 in 1997 seems a bit out of sync. How do your plugs look?

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 09/17/2007 : 14:52:31

Is the Johnson running smoothly? Are the plugs fairly clean and properly gapped? Have you tried running it any leaner? Does the Merc run on 40:1? My last 2-stroke was a 4hp Yamaha that ran 100:1, and it made only a whisper of smoke. Obviously, the more oil in the mixture, the more smoke, and all 2-strokes make some... (Then there are the twin-200+ 2-strokes that drive everyone out of the marina when they start up!

)

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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 09/17/2007 : 15:58:14

Joe & Dave,
Thanks for the advice, I think you might be on to something. I'm pretty sure I never actually looked up the mixture ratio, I just followed what the PO told me...I think. I'll look up the proper ratio in my book next time I'm down on the boat and go from there. I'll also take a look at the plugs. I know the engine was serviced right before I bought it (I have the receipt), so the gap should be in good shape. I know what leaning the mixture means, but not sure how to do it on this particular engine. I'll look it up, maybe it is running rich as you suggest.

I never really thought all that much about the smoke till one of my friends poked fun at me for it. Then on the last two trips where we motored a long way I found myself constantly with a nose full of smoke as we motored (hence the irritated comment). I'll look into your suggestions & see what I can come up with. If I'm mixing wrong, I've got one more tankful to go, although I can do the math & add some un-mixed gas to lower the ratio.

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dmpilc
Master Marine Consultant

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USA
4593 Posts

Response Posted - 09/17/2007 : 16:31:47

Changing to 50:1 will lean the mixture. When you've got about 1 gallon left in the tank add a gallon of 50:1. Run that down to about 1 gallon and keep repeating the process. You should see a reduction in the amount of smoke.
I went to the iboats.com website. They have a forum where you can ask questions about outboard engines. I found several about oil/gas mixture. From some of the responses I saw, your motor is very likely to use a 50:1 mix. For a very brief period they tinkered with a 100:1 ratio, but ended up issuing a service bulletin to change those motor's decal to one reading 50:1. hope that helps.

Edited by - dmpilc on 09/17/2007 16:47:27

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 09/17/2007 : 17:06:26

I think the math works out to this: Run the 6.5 gallon tank down to 5 gallons (of 40:1), add 1.25 gallons of straight gas, and you have 6.25 gallons of 50:1. Somebody check that!

Your PO may be referring to the instructions for his weed-eater or something--I doubt that Johnsons specified that much oil. I'd start there, and then (if you don't see much improvement) move on to leaning out the fuel-air mixture. Your owner's manual should show you where--there might be two screws, for the idle and high-speed jets. Unfortunately, that's a job that should be done under way so you can hear the changes, which could be tricky on these boats. I generally have only done it when flushing or checking out an engine in a tank.

Edited by - Dave Bristle on 09/17/2007 17:16:45

Steve Siefken
1st Mate

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USA
81 Posts

Response Posted - 09/17/2007 : 18:32:29

David,

I am running a Johnson Sailmaster too. It is a 1996 9.9 HP 2-stroke. I have the manual for the engine on the boat but I am pretty sure it calls for a 40:1 mixture. If it is different that that I will let you know.

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Stu Jackson C34
Admiral

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844 Posts

Response Posted - 09/17/2007 : 19:04:40

Some of the Johnson and Evinrude engines of that era have an external adjustment for the idle and high speed jets. Or, that may be another adjustment, and I would really like to know what it's for

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dmpilc
Master Marine Consultant

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Response Posted - 09/17/2007 : 20:47:00

Dave B., I appreciate the math calculation and agree that your approach would give David (we've got a lot of Davids on this forum don't we, so call me David P.)an immediate shift to 50:1. I know little about ourboards, so I suggested a method that would gradually shift him from 40:1 to 50:1 thinking it might be better for the engine. Maybe that's not necessary.
David P.

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ClamBeach
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3072 Posts

Response Posted - 09/17/2007 : 22:00:59

I think 40:1 versus 50:1 probably isn't going to make a huge difference in the smoke level (Provided the current mix is an accurate 40:1). Could also be clogged ports, weak compression, a rich mixture, etc.

I've found that the brand/type of oil can make quite a difference too. Clean burning synthetics leave a lot less carbon residue and produce less smoke.

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GaryB
Master Marine Consultant

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4303 Posts

Response Posted - 09/17/2007 : 22:55:50

When I was a kid back in the early 70's we had a 100HP Evinrude on our power boat and it was 50:1. I believe that in the late 60's early 70's Federal Laws were changed requiring the mix go to 50:1 to reduce pollution. Of course things could have changed again although I doubt it. Check your manual is the safest thing to do.

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BruceL
1st Mate

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USA
30 Posts

Response Posted - 09/18/2007 : 00:16:16

Dave
I have the same motor and run it at 50:1
I too notice that sometimes there is an excessive amount of smoke when the motor is cold or when it is cold outside.
I just thought that it was because of where the motor vents remember it's not through the prop like on the merc.

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Chris Z
Captain

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452 Posts

Response Posted - 09/18/2007 : 02:31:46

Boy, I sure do miss my old 2 stroke

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DaveR
Master Marine Consultant

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USA
2015 Posts

Response Posted - 09/18/2007 : 07:53:51

I've got a '74 Johnson 50 on my 14' trihull that uses a 50:1 also.
Chris Z; What's so awful about your 4 stroke?

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 09/18/2007 : 08:11:19

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by DaveR
 Chris Z; What's so awful about your 4 stroke?<hr height="1" noshade id="quote"></blockquote id="quote">Some people don't feel like they're around boats unless they smell that half-burned, atomized oil and smoke, and see that lovely rainbow slick on the water.

Edited by - Dave Bristle on 09/18/2007 08:13:09

Chris Z
Captain

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452 Posts

Response Posted - 09/18/2007 : 08:22:23

Dave, I love my love my 4 stroke on my fishing boat and C25. Just a little pun on 2 strokes. I swore off 2 strokes after buying my 9.9 4 stroke for my fishing boat. Cut my gas usage by half, no loud engine, more torque/power, and no smell, when trolling for walleyes on calm days. Another good note, I switched from a six gallon tank to a three. Cut out more weight.

I was told by the dealer that mine might cut fuel usage near half, well it has been more than half.

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tinob
Master Marine Consultant

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USA
1883 Posts

Response Posted - 09/18/2007 : 13:59:01

SMOKIN DAVID,

My last Johnson 2 stroke was a 1993 9.9 hp and the mixture when first set up was for 100:1. Soon after that the dealer sent a notice to increase the oil/gas ratio to 50:1, it has been that way since.
I'd advise that you don't go messing with carburetor fuel mixing screws. Fuel air mixtures are for the experienced to do. The expression, "SCREWED-UP" is perhaps where inexperienced carburetor adjusters held court. I've never adjusted the carb on my old Johnson, sailmaster in the 12 years I ran it. Wasn't needed.

Val on Calista # 3936, Patchogue, N.Y.

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