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TOPIC: Crazy historic V4 fuel wasting exposed!!!!

Crazy historic V4 fuel wasting exposed!!!! 7 years 1 month ago #43007

  • jepstr67
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I've been trying to purchase an Evinrude Playmate all summer. The fellow who has it is a perfectionist who won't let me take it until is in A1 shape. It has been sitting in his boat museum for 10 or more years, so it needed some TLC.

In the process of restoring the the DU motor (which runs like a Swiss watch now :) ) A gasket got folded over and caused an unexplained fuel leak. Further examination shows that it is an elaborately cast passage in the block from the carburetor directly to the exhaust! Try as we might, we can't figure why on Earth they would have designed it that way. The mechanics looked at an outboard V4 and discovered it was made the same way.

Any ideas as to why there is this fuel overflow directly into the exhaust? Even more important, if it serves no purpose as an "after burner" could that fuel be captured and returned to the fuel tank? I gave it a quick look, and it does seem like it would be possible to tap the passage and rout the excess fuel into ta pipe rather than into the exhaust.

This is going to bother me EVERY time I fill with gas now, so let the discussion begin!

Todd
1965 Evinrude Playmate and many Larsons.

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Re:Crazy historic V4 fuel wasting exposed!!!! 7 years 1 month ago #43036

I have no idea why or even exactly what gasket and passage you are refering to. I have never had to disect my DU.

But, trust me it will be a fuel pig regardless of fuel leakage or not. I have 155 HP V6 powered boats & they both get better mileage with less noise, lots less noise.

Jim

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Re:Crazy historic V4 fuel wasting exposed!!!! 7 years 1 month ago #43041

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I was actually looking for more useful comments related directly to the DU or V4 outboard, but that is good to know that a V6 gets better fuel economy.

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Re:Crazy historic V4 fuel wasting exposed!!!! 7 years 1 month ago #43065

OK, for starters if that unit is still original 1965 vintage, then the drive will have 4 bolts on the top cap. The unit was assembled with matched parts and does NOT use shims.

The intermediate has a grease fitting up where the oil fill plug is located on later units. Remove the screw plug next to it prior to greasing the drive or you may push the grease seal out.

If that is an oil injected engine, expect distributor drive belt issues. The non oil injected engines have much better drive belt life.

The carbs (2 each) have indiviual metering circuits for each cylinder but feed off common fuel bowls. If Cyl 1 & 2 (or 3 & 4) are flooding, the carb bowl is most likely flooding.

The ignition system uses two sets of points. Cyl 1 & 3 share one set and 2 & 4 share the other.

So, bottom line is a problem paired with cyl 1 & 2 (or 3 & 4) is most likely fuel. Problems paired with cyl 1 & 3 (or 2 & 4) is most likely ignition.

There is a filter element in the fuel pump. If it plugs, the boat will most likely plane out then loose power. I doubt you will find them new. I successfully cleaned one once. Better solution is to remove the filter element & replace it with a water seperating spin on filter assembly between the tank & the pump.

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Re:Crazy historic V4 fuel wasting exposed!!!! 7 years 1 month ago #43108

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This fuel gushing into the exhaust system would be related to the common fuel bowl. As I said both mechanics, who have been working on old Evinrudes since the 1960's and myself can't figure out what purpose this passage serves. I wanted to get a few photos but I did not have my camera when I stopped at their shop. I will be able to get some better visual aids and photos to explain the odd design in a few weeks. The question still remains, what purpose does it serve to have a port from the float bowl to the exhaust chamber? It can't be an overflow. Why? The floats would cap off fuel from coming in before that were necessary. It can't be a vent because there would be back pressure on it when the motor is running. unless.... it is a vent.....(thinking out loud) Where the theory was that before the motor was running it would act as a vent, but then exhaust pressure would keep fuel from passing into the exhaust once the motor was running.

Good to know the oil injection is problematic with belts. I have one I thought about installing just for the novelty of it. I think I'll get a second engine block and make a display of how it works rather than using it on the boat. I don't want to toast my motor for lack of oil.

Time will tell.

Todd

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Re:Crazy historic V4 fuel wasting exposed!!!! 7 years 1 month ago #43110

OK, the carbs are down low, way low as in under the engine. Regardless of 2 stroke or 4 stroke, they are an inboard and fuel leaks need to be anticipated.

If the float stuck, needle leaked or for what ever reason the float bowl flooded, that fuel needs to go somewhere other than in the bilge. My guess is that it is a vent/overflow. Just imagine that electric fuel pump pumping 12 gallons of fuel into the bilge.

Assuming the needle/seat and float are working correctly, the fuel would never reach a level to flow into the exhaust.

BTW, on a conevntional 4 stroke I/O, the carb bowl vent would overflow directly into the venturi and flood the engine until it quit. Raw fuel would not pump after it quit because it used a mechanical fuel pump. Later GM based I/Os without the provisions for a fuel pump used an electric fuel pump that relied on oil pressure to actuate a switch that completed the circuit to operate the pump. Engine dies & the pump is shut off.

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Re:Crazy historic V4 fuel wasting exposed!!!! 7 years 1 month ago #43114

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Good point. If it does overflow, that would be one of the only ways to keep it out of the boat. When the passage in the power head gets into the rear casting, it takes a vertical bend and the exit port is about 3" higher than the carburetor bowl. Perhaps when it is assembled correctly, without the gasket folded and leaking, there is very little fuel transfer to the exhaust area. That theory only works for the DU, not the outboard.

I'm more than a little curious what would happen if I put a typical marine Rochester 2G carb on a DU motor...?

My automotive teacher in college said "the worst thing about carburetors is they are right on top where people can fool with them." Not so with boats.

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Re:Crazy historic V4 fuel wasting exposed!!!! 7 years 1 month ago #43164

jepstr67 wrote:

I'm more than a little curious what would happen if I put a typical marine Rochester 2G carb on a DU motor...?


You would need to fabricate some type of manifold to adapt the carb to the intake manifold assy. Then the linkage would also need to be fabricated. Remember, your throttle linkage also turns the distributor at a calibrated rate to syncronize the timing to the throttle.

Personally, I see very little reason to adapt anything. The engineers did what they did for a reason. Cost, safety & reliability all were factors they considered at the time.

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Re:Crazy historic V4 fuel wasting exposed!!!! 7 years 1 month ago #43192

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Some people ask why, others ask why not.

Fortunately there are still a few who ask why not.

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Re:Crazy historic V4 fuel wasting exposed!!!! 7 years 1 month ago #44895

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Just as a follow up, with the correct gasket in place, it plugs the fuel wasting holes.

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