excessive gas coming out of exhaust port

[paawe123]

I just picked up a 1958 10 HP Johnson QD-19. There seems to be a significant amount of un-burned gas that is coming out of the exhaust port. While running at a slow/idle speed there will be a sheen on the water from port to starboard at the transom (approximately 5.5 feet) and the sheen will go back several feet behind the boat. I know it is un-burned fuel and I know that the older 2-cycle engines will not consume all the gas but the amount of un-burned fuel seems to be excessive. Prior to the QD-19 I had a CD-14 (57 5.5 HP Johnson) and that engine would put out some raw gas but the volume was not a point of concern. The QD-19 will also release significant amounts of the un-burned fuel after shutting the motor off. What are the causes of excessive fuel discharge from the exhaust port?

[fisherman6]

Do you know when the last time this engine was tuned up was? There will be a certain amount of unburned fuel mix expelled, but what you describe certainly sounds excessive. What spark plugs are in the engine? Is is possible it is only running on one cylinder at low speed? That is one possible cause of excessive amounts of fuel to be exhausted.
-Ben

OldJohnnyRude on YouTube

[paawe123]

Thanks for your response. I was told it was recently tuned and it does run nicely at both faster and slower speeds. Off the top of my head I do not know what plugs are in it but the guy I bought the motor from works on these old outboards as a hobby and post videos of the outboards on youtube under outboardfun. I am thinking something has happened after I picked it up because I would have noticed the mount of fuel that I am seeing in the video of the motor,as posted by outboardfun, I bought.

[fisherman6]

I have never bought a motor from outboard fun but I ame.familiar with his videos and know someone who bought one of his motors. It was in excellent condition when received and I have every reason to believe he does excellent work. I’m not sure what may have happened to his motor in transit but anything is possible. If he said he tuned it recently I would believe it. He tends to have quite nice very well-running motors.

Is it possible you are idling the engine before it is up to full operating temperature? That would also be a possible cause. If it is running on both cylinders, it seems rich. Have you tried making any carb adjustments? Do you know how to adjust the mixture screws properly? The needles certainly could have gotten moved in transit. Just looking for possibilities of what may be going on.
-Ben

OldJohnnyRude on YouTube

[david-bartlett]

That motor does not have a thermostat, and when running slow it will not get hot enough to "burn" all the fuel that goes through the motor. Running fast is better, but these motors are not real efficient.

If you are feeling guilty about the environment, remember that you are helping to keep junk out of the landfill by running an older motor.

[sydinnj]

Actually if I remember right it is the oil that leaves the colored sheen not the gas, if so is it too heavy on the oil, beside the above reasons

[The Boat House]

What your seeing is mostly oil not fuel.
Today’s oil doesn’t burn like the oil from
the past did. A lot less smoke and the carbon
deposits are almost non existent in the
Pennzoil synthetic oil I have been using
but I suspect today’s conventional oil performs
much the same. How much residual oil you
have is relative to the type and amount of oil
you run. How does what your running compare
to what the seller uses in type and amount?

[paawe123]

Thanks for your responses. Gives me some ideas to try and tweak a few things to reduce the un-burned fuel. As to the Outboard fun guy; yes I believe he does very good work w/ these motors and that is one of the reasons why I purchased this motor from him.

[fleetwin]

Unfortunately, what you are seeing is considered fairly normal for these engines. There is a crankcase drain that discharges puddled fuel/oil out the exhaust, and the engine does not have a thermostat so it tends to run cold at lower speeds. You should be using the champion J6C plugs gapped at .030". Please do not cut back on the oil mix in an effort to reduce this emission, in fact I would use 16:1 on this engine due to its lack of wrist pin needle bearings.
All that being said, it surely is possible that there is a slight fuel leak at the connector or somewhere under the hood causing the sheen you are seeing. You might try running the engine with the cover removed after cleaning the engine pan with degreaser, to check for leaks.

[raglover]

Agree with all that has been said, probably normal. One thing to check, is he low speed needle too far open, making it really rich?

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