Stock Opti cowl vacuum

[TheRubberDuck]

Hello all. I replaced my 250 Pro XS cowl with a CDR Alien cowl. I was looking at the stock plenum that came off the motor under the stock cowl. I noticed it had what looked like a vacuum port that went to the 2,4,6 cylinder head.

The CDR cowl doesn't have this and there is just a 3/4" barb fitting sticking up on that head. What is that? Do I need to address it? Thank yall

[JOE54]

there are no vacum ports on the heads , either one , would like to see a pic of this fitting please

[lpugh]

I think he is referring to the air compressor intake fitting

[JOE54]

god i hope so LEON

[TheRubberDuck]

Hope this works, I circled it. If not, I'll have to wait till I get home.

[lpugh]

did you put the yellow cap on there, must be kept open as that is the air intake for compressor.
Recommend you run the stock cowl as it connects to that port and will help avoid foreign objects getting sucked in the compressor.

In fact, the AM cowl may provide different flow rate to motor upsetting correct air fuel ratios.
I would not want it on my motor unless i also had software in the computer that was mapped for using that cowl.

[TheRubberDuck]

I did not block it off

[lpugh]

Motor should not run with that capped off!
start and stall maybe>
Is this a new compressor or powerhead?
Is there a hole in the yellow cap to allow air flow.
need to know the rest of the story here!

[TheRubberDuck]

To clarify...... That is not my motor. It's a photo off the web.

I DID NOT cap anything off. The motor runs fine. I just noticed that the stock plenum that mounts on the motor had a "channel" that went from that nipple to the same area as the throttle body.

I thought it was some kind of vacuum. Air pump feed makes sense.

I agree it doesn't need to sit "open" so to speak. It should have a hose about the same length as that "channel" up by the throttle body just to keep the air clean and not injest water in a washover situation.

I think that covers it. LOL

[TheRubberDuck]

I've had that cowl on since May with no issues. I was just cleaning some stuff up in the shop and picked that stock plenum up and went.....hey, is that a vacuum port? I will have to take a pic of it in the morning when I get home.

[TheRubberDuck]

But now you got me questioning the air/fuel ratios. I saw that there are gauges for that. I need to know where to get that I suppose.

[lpugh]

But now you got me questioning the air/fuel ratios. I saw that there are gauges for that. I need to know where to get that I suppose.

No such thing as gauges for AFR, you are seeing air/fuel pressure gauges. To test AFR requires a exhaust gas analyzer. Very difficult to do on outboard motors due to water in the exhaust system which would destroy the gas analyzer, manufactures have equipment to do this on a dyno while sampling the exhaust gases. With that information they can adjust AFR and timing curves for optimum setting in the software.
Anything that changes air flow requires changing the computer programing.
Got to very careful with any mods on these motors.

[TheRubberDuck]

I agree with what you are saying Leon, and I certainly appreciate your input. Y'all will have to forgive me. While I am a gearhead, I'm all new to this engine/performance world. But I'm learning!!! Thanks again to all!

[JOE54]

that flywheel cover helps to maintain normal debri /belt material that will be lost under normal use from being ingested into engine and air compressor intake you are referring to and route clean air to compressor , QUESTION: is the front piece of this 2 part cover removed also ???

[EuropeanAM]

that flywheel cover helps to maintain normal debri /belt material that will be lost under normal use from being ingested into engine and air compressor intake you are referring to and route clean air to compressor , QUESTION: is the front piece of this 2 part cover removed also ???

STRONGLY recommend the flywheel cover remain in place. As stated, the fitting you described is part of the Flywheel Cover (NOT part of a cowling). It helps to direct where the air compressor is getting it's air from, and also aids in helping to prevent water being ingested as easily in the event of a more "aggressive backwash".

[TheRubberDuck]

I have both pieces removed because they won't fit under the CDR plenum. Instead of leaving it open like it is now, I will route a hose from the air pump nipple to the throttle body area like the flywheel cover had it with the open end pointing down. That should keep water and debris out of it.

Honestly I would love to put the stock piece back on over the throttle body just for the sound alone. The CDR cowl is cool, but it sounds terrible.

[JOE54]

STRONGLY recommend the flywheel cover remain in place. As stated, the fitting you described is part of the Flywheel Cover (NOT part of a cowling). It helps to direct where the air compressor is getting it's air from, and also aids in helping to prevent water being ingested as easily in the event of a more "aggressive backwash".

^^^^^^ STRONGLY +2 , well lets get er dun then thats very a simple problem to rectumfy

[TheRubberDuck]

Gentlemen I finally got around to redirecting the compressor intake. It took several renditions to get it to clear the CDR plenum. I had to cut down and re-tap the 90* male to female just to be able to thread it in. But I think we have a winner!

[lpugh]

No sir you do not as you have reduced the air flow to the compressor, system air and fuel pressures may be reduced under high load conditions. I know these motors very well and I keep it as delivered from Mercury. May get away with, may not!

[TheRubberDuck]

I was about to disagree on the restriction….. BUT, again you got me thinking. The stock fitting threads that go into the 90 may be protruding into the air path. So I will go back in and correct that. After that, no restrictions as everything will be the same size as the stock fitting internally. And the hose itself is a better/smoother path than the flywheel cover path.