Unburned fuel

[mikeg]

What did OMC do to eliminate unburned fuel from running down the leg
of the RD’s and what year ? I’ve had onlookers making mention of the
rainbow from my motors, while complementing my old boat. I am
planning on adding a fuel recovery to eliminate any chance of complaints.

[wiscoboater]

You might try going up 1 heat range in plug and making sure your points, coils and plug wires are in top shape. Another thing to try is FrankR’s timing tools to be sure your spark timing is optimized. Franks tools are top notch and will really get you dialed in. With the hugely oil rich mixtures needed in the RD series of motors I do not think you will ever eliminate the "floating rainbow" completely. If it’s an environmental concern, look into some of the biodegradable 2 stroke oils offered.

[Casey Lynn]

Also check your gearcase oil to make sure it is not leaking water in and gear oil out. That can definitely leave a rainbow….

[frankr]

1st, you have to realize that all two-stroke engines emit SOME oil out the exhaust. If they did not, there would be no lubrication in the piston/rings/cylinders in the exhaust port area. But it is a matter of how much emissions bother people. I think your real question is when did they stop putting crankcase drains in OMC motors. It wasn’t an across the board swoop. More of a phase-in as technologies developed. But I’d say the efforts began in the late 1960’s. The 1968 55hp looper would be a good example.

I agree, if you are concerned, use 100% Synthetic outboard oil, then point out to critics where it says bio-degradable on the jug. Won’t do any good, but might shut them up long enough to make a hasty departure.

[hugh]

I went to the Synthetic in all my smaller motors 50 and down as I do go to a lot of pretty highland lakes. My 85 hp will just have to make do on the cheaper stuff though. My wall rack has a drip pan under all the outboards as it seems they will drip oil for months after being ran 😆 2 Strokes, gotta luve um.

[crosbyman]

XD-100 biodegradable.. no smoke no smell

Joining AOMCI has priviledges 🙂

[r-c]

OMC came out in 1970 or 71 with a crankcase recycle system across the line. They simply took the puddling of fuel (at idle) in the bottom of the crankcase and routed it back to the intake covers to be re-burned. The 40hp (built like a 50’s "Big Twin") did this. It had to help as my 58 35hp makes more of a rain bow than the 73 40hp I use on my user boat.

[vintin]

I recover mine in a one gallon tank. 57 35hp Johnson. I’ve often wondered about the composition of what is recovered. I pour in into the main tank and it looks to be oil rich.

[bill-mcnamara]

I have several RD’s on the go now, and also cringe at the rainbow as admirers check out the wooden boats at the docks.
I’ll be adding twin ’56 Javelins to the fleet on the latest project this Summer, so this is a good chance to finally get around to equipping them with fuel recovery systems .Shouldn’t be too difficult to plumb two collection tubes into a single collection bottle.

Having two "hydrocarbon donors" doing their thing at the same time, would certainly detract from the love-in.
I do remember several descriptions and guidelines of "how to do" from the previous board, which I’ll have to try and find.

Re: synthetic/biodegradable oils, I’m sure that Frank’s comments are spot on, better to try and catch the ooze at source.
I’ve been using OMC oil, but open to suggestions…..

[david-bartlett]

I find I get a lot less rainbow if I run the motor pretty hard, as opposed to lots of slow speed, idling, trolling etc.

Th RD size motors are very inefficient for that type of use. Not real efficient at speed either, but lots of fun! Synthetic oil will help, but will not eliminate the rainbow.

I have realized that you cannot please everyone, so now I spend more time doing what makes me smile.

[Author]

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