Unburned fuel/oil recycling mod

[outboardnut]

Is there a way of recirculating the the unburned fuel into the "system" with out collecting into a container?

[chris-p]

Yes.

I have done a few Big Twins, that installed a fuel pump on for others.

I kept the original motor male fitting though from the pressure system. The recycle line, I plumbed into the old AIR line, then plumbed that into a fitting on top of the tank. Looks original, most would not even be able to tell what was going on there.

Only advice with that, is to try to run the tank close to out, then fill fresh with new mix. If you top it up all the time, your overall mix could get away from you.

[mr-asa]

quote WetWillie:

I am hesitant to start a thread on this topic because I am by no means an authority on this mod.

To my mind, you already have started a thread on this. Please, please don’t let that be a barrier to your posting. Post a disclaimer at the top and let anyone who reads it know that you aren’t an expert, and the experts will chime in. None of us will get upset that you might not know everything, and if we don’t share information with each other freely then the forum will wither and membership will die off.

[wetwillie]

Well, if you’re going to put it that way 🙂 I’ll take a shot at it.
1st the disclaimer and some background: As stated earlier, I have done this mod on 2 Evinrudes, a ’56 Big Twin 30 and a ’66 Ski Twin 33. I did it because there was so much unburned oil bubbling up in the exhaust at idle that I thought my lower unit had a leak. I drained the lower unit and determined the lower unit seals were fine. I figured, correctly, that the oil was coming from the exhaust cavity. It was draining into the cavity from the crankcase.
To perform the mod, you must remove a small cover located to the lower right of the carb, close to the bottom of the crankcase. I placed a screwdriver pointing to the cover in the pic I took.

I drilled and tapped that cover in the lower corner of it, looking at the underside first to determine the best location. I then screwed in a barbed fitting which I sealed in place with JB Weld. FWIW, the cover on the ’56 Big Twin is identical to the cover on the ’66 Ski Twin. The only difference is the amount of available space for the fitting. I had to angle it on the ’66 vs straight out on the ’56 which has more space available.

There is a spacer, of sorts under the cover which also has to be removed in order to access the drain hole located underneath. I plugged that hole with silicone. Plugging it forces the unburned fuel/oil to drain out through the barbed fitting. I reinstalled the spacer and the cover before connecting a hose to the barbed end and running it to a container that I purchased at a "Dollar" type store.

I was surprised at just how much unburned fuel/oil mix collects into the jug, especially at low RPM. I was especially happy that there were no longer any globules of oil bubbling up in the exhaust.
Let the comments begin. 🙂

[vintin]

I’ve seen separators for sale on eBay for later motors that direct the vapors back to the carb and the liquid collected is pumped back into the carb fuel line. No capture tank needed. This is quite an expensive set up.

I’ve posted about my set up before on my 1957 35hp RD. I use a separator and route the vapor back to the air box via the carb fogging opening and collected liquid gravity drains back to a Moeller 15 gallon main fuel tank. I’ve got a fuel pump on this motor. The separator is an air compressor water separator.

After crankcase pressure pushes the liquid out via the crankcase drain reed valve assembly there is a surprising volume of fuel/air mix that also ends up being discharged. I’ve captured this fuel/air mix and am burning it. Surprisingly the inside of the air box stays clean which was a concern of mine.

My earlier system collected liquid in a one gallon tank with vapor going to the air box via a second connection to the tank. It got old emptying the one gallon tank.

[Author]

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