Bleed System Alternative?

**Glastron1987** · 03-19-2021, 08:20 AM

The Merc bleed system always seemed a little hokey to me, but I guess it's better than not using it.

My understanding is that for some reason fuel pools in the bottom of the intakes and the bleeds clears that out. The problem I see is that all this work is done by the carbs or EFi systems to precisely meter the air/fuel mixture, and then this is short-cut by dumping some random amount of fuel directly into the intake past that metering.

Is there a better alternative to this? ...like reshaping the intakes so the fuel does not pool, or rerouting all the bleed lines to the input side of the fuel pump?

**Smalltownbassin** · 03-19-2021, 08:29 AM

I thought is was mostly for ensuring proper lubrication?

**David - WI** · 03-19-2021, 08:54 AM

The "better" way is to inject the fuel after the reeds like a 260 rather than using carbs or Laser-style injection; so that fuel doesn't collect on the reeds and run off in huge droplets.

The fuel only drops out of suspension and pools at very low airspeeds (idle) when the reeds don't open very far; and the bleed system really just keeps you from getting a big puff of smoke when you trim the motor back down to take off after a "slow - no wake" or when you're done trolling for fish.

**InjectorService** · 03-19-2021, 03:13 PM

Maybe a little off track:

So what do the bleed lines on the Optimax do? Just for oil?

**David - WI** · 03-19-2021, 03:45 PM

Originally Posted by InjectorService

Maybe a little off track:

So what do the bleed lines on the Optimax do? Just for oil?

That's what I would think, "re-circulating" oil from the crankcase that's pooling up in the transfer port back out to the intake port?

**FUJIMO** · 03-19-2021, 09:03 PM

...this might date me but...there used to be a bleed line that went up to the top main crank bearing as well...for its lubrication...

**tnelsmn** · 03-19-2021, 10:32 PM

All of my bleed lines look like they aim at the mains. I always thought they were there for more lube to the bearings.

**tlwjkw** · 03-20-2021, 04:25 AM

Originally Posted by tnelsmn

All of my bleed lines look like they aim at the mains. I always thought they were there for more lube to the bearings.

tha ones going to tha mains (two center and bottom ta top) are not "bleed lines"..... just look like it.

**Glastron1987** · 03-20-2021, 08:20 AM

Originally Posted by InjectorService

Maybe a little off track:

So what do the bleed lines on the Optimax do? Just for oil?

Not that I have worked with one, but I thought there was no need for bleed lines on the Opti's because of the direct injection to the cylinder chamber. Any lines that look like bleed lines I think would be oil lines to the different parts of the engine that need oil.

**tlwjkw** · 03-20-2021, 08:35 AM

Originally Posted by Glastron1987

The Merc bleed system always seemed a little hokey to me, but I guess it's better than not using it.
Is there a better alternative to this? ...like reshaping the intakes so the fuel does not pool, or rerouting all the bleed lines to the input side of the fuel pump?

i would think that if there was a "better way" someone, somewhere would have come up with something between 1976 and last year of tha V6 2 stroke (other than tha opti pops)... jmo.

**David - WI** · 03-20-2021, 10:34 AM

Originally Posted by Glastron1987

Not that I have worked with one, but I thought there was no need for bleed lines on the Opti's because of the direct injection to the cylinder chamber. Any lines that look like bleed lines I think would be oil lines to the different parts of the engine that need oil.

Except that you can see the bleed lines going up front and dumping into the side of the reed plate.

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**InjectorService** · 03-20-2021, 11:28 AM

Looks like David beat me to it. But this is from the 300xs service manual. Looks like they are essentially doing the some job as typical bleed lines, only for oil instead of fuel. If I recall correctly there are check valves on them as well.

Blake

**Glastron1987** · 03-20-2021, 05:37 PM

Maybe not as hokey as I was thinking.

**25two.stroke** · 03-22-2021, 06:00 PM

Whats not being stated here clearly is theres 2 types of bleed lines: those for fuel and those for oil. Yeah the optis ONLY have oil because no fuel goes though the intake. Merc calls them bleed lines because not that much volume goes through them, but realistically they are oilier lines that go to strategic (places like bearings) to provide precise location and amount of oil - so the 2 stroke stays lubricated but doesn't burn excessive amounts of oil.

On a non direct-injection motor the line FUJIMO is referencing is a single line with no tees or interruptions that goes from the bottom of the crankcase (where oil tends to pond) to the top crank bearing that doesn't get much oil via the natural fuel induction flow. This has a check valve to ensure directional flow. This cant really be made better unless you made a passage in the crankcase and somehow had a serviceable bleeder in it (cause they get clogged).
The bleeder lines on carb motors that go from the cylinders back to the intake are scavenger lines that burn that fuel that tends to build up at low rpms as mentioned above.

The crankcase injection motors also have a set of scavenger lines but they only go from the reeds back to the intake, not to the cylinders. I've been wondering about that for a long time and ween a real oldster who developed these things to explain why in the world the crankcase injection motors still have bleed lines but they go the opposite direction as the carb and TBI motors.

**NeedOne** · 04-07-2021, 08:07 AM

Adding this Question here rather than start another thread...
200 w/ Laser EFI ... I redid the bleed lines in Tygon... watching it run @ idle, was surprised by the volume of fuel flowing in the bleed lines!
My expectation was that it scavenged a miniscule amount of extra fuel and would be mostly air, but is basically flowing fuel.
Is this normal operation?