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1999 90 Johnson Air Silencer ... does it need to seat tightly?

H

humm9er

Member
So one of my low-speed carb jets plugged up, and i believe it was a piece of fuel hose breaking down (thanks ethanol!).

I had replaced all fuel lines from tank to motor years ago with new A1 ethanol resistant hose.

It occurred to me when this happened that my fuel hose from the side of the motor cowl to the VRO (OMS), and from the VRO to each fuel rail was still original and possiblydegrading. SOOO, I replaced those lines with new 3/8 and/or 5/16" A1 fuel hose. But the issue is the new hose is so much thicker, my air silencer still seats on the rubber carb "gaskets" but doesnt seat quite as tight as it used to.

Will this be an issue (ie will it cause engine to run lean or anything)?

Thank you!!
 
Tim, thank you -- okay so no issue. I recall reading somewhere it could run the engine lean but I dont really see how that's the case...those covers dont appear to be too sophisticated so I have a hard time seeing how they'd change the air metering too much.
 
Exactly, very good reasoning, Hummer. The problem with outboards is that at low speeds, the exhaust may "pool" around the transom and substantially corrupt the mixture anyway. Of course this scenario will create a richer mixture because of contaminated and oxygen depleted air. Once underway the mixture will stabilize. Your very welcome.
 
Okay, Chris is right. Except for OMC 100:1 outboards and "AutoBlend".......and a few other exceptions.
 
I did put it back. My question is if the air cover seats a bit less tightly against the rubber rings on the tops of the carbs, do we think that's an issue? If so, I will have to remove the new manifold fuel hoses and go back to the old style hoses, which may be deteriorating.
 
Perhaps there is a misunderstanding here. If the intake air has a minimal entrance at the carb throat seal, it should not make any difference. If the silencer is completely removed, it may allow too much air and then lean the mixture. For performance sake, as a general rule......the more air and fuel can enter a combustion engine, the more power can be generated. Hense turbo and supercharging, ram air, blowers, etc. (See Chris's motor in avatar) The fuel then has to be enrichened correspondingly to ensure against engine damage from an overly lean mixture.
 
Fuel injected now.

2nd.jpg
 
Johnson/Evinrude airboxes are designed for each carb/motor set-up. The late 80's-early 90's V-6 had a restrictive airbox, removing it resulted in idle issues and lean on top end scorched pistons. Your 60 degree 90 motor has a less restrictive box but needs to be seated as snug as possible. Here is a lil reading info..


[h=1]Your Airbox, Friend or Foe?[/h]
Separate the Fact from the Fiction
By Lonn Peterson/Thunder Products Inc​
There is a very common belief that getting rid of all the restriction from the air box is about the best thing you can do. Wow! Just think of all the horsepower, and it’s practically free. Isn’t it strange then, that all the manufacturers build model after model, year after year with those restrictive air boxes? Don’t they read the same magazines we do? If they did, they would certainly learn about all of the ways to get rid of all that nasty old restriction, right?
Maybe not. Let’s look at the physics of how fuel enters your intake system. The atmospheric pressure exerts force on the fuel in your float bowl, forcing it through your jetting circuits, into the air stream passing through your carburetor. In order for this process to work, the internal pressure in your carburetor must be lower than atmospheric. Pretty simple. If you have removed your air box, cut a number of holes in it or are running without a lid, you may be in for a surprise. Your internal pressure is now nearly the same as atmospheric, making fuel delivery difficult.
Engineers call the difference in pressure a pressure drop differential. A particular amount of restriction (some call it vacuum) provided by your air box keeps the internal pressure lower than atmospheric, insuring consistent fuel delivery over a wide range of temperatures and altitude. Without an acceptable pressure drop differential, the engine will be fussy about changes in jetting to maintain performance.
Another aspect that affects pressure drop is air speed (velocity). Simply put, the higher the air velocity in the carburetor, the lower the internal pressure. When you attempt to operate with a wide open air box or with the lid off, the air velocity is actually slower (yes slower) due to the enlargement of the intake opening. You now have plenty of air; however you also have poor air velocity. Velocity is needed to atomize the fuel and produce quick throttle response. This slower air speed promotes higher internal pressures, closer to atmospheric, hindering fuel delivery.

​
 
humm9er said:
I did put it back. My question is if the air cover seats a bit less tightly against the rubber rings on the tops of the carbs, do we think that's an issue? If so, I will have to remove the new manifold fuel hoses and go back to the old style hoses, which may be deteriorating.
Click to expand...

Could you make a tighter seal by using two sealing rings for each carb intake.

Just an idea . Apologies if it's a dumb one.
 
faztbullet said:
Johnson/Evinrude airboxes are designed for each carb/motor set-up. The late 80's-early 90's V-6 had a restrictive airbox, removing it resulted in idle issues and lean on top end scorched pistons. Your 60 degree 90 motor has a less restrictive box but needs to be seated as snug as possible. Here is a lil reading info..


Your Airbox, Friend or Foe?


Separate the Fact from the Fiction
By Lonn Peterson/Thunder Products Inc​
There is a very common belief that getting rid of all the restriction from the air box is about the best thing you can do. Wow! Just think of all the horsepower, and it’s practically free. Isn’t it strange then, that all the manufacturers build model after model, year after year with those restrictive air boxes? Don’t they read the same magazines we do? If they did, they would certainly learn about all of the ways to get rid of all that nasty old restriction, right?
Maybe not. Let’s look at the physics of how fuel enters your intake system. The atmospheric pressure exerts force on the fuel in your float bowl, forcing it through your jetting circuits, into the air stream passing through your carburetor. In order for this process to work, the internal pressure in your carburetor must be lower than atmospheric. Pretty simple. If you have removed your air box, cut a number of holes in it or are running without a lid, you may be in for a surprise. Your internal pressure is now nearly the same as atmospheric, making fuel delivery difficult.
Engineers call the difference in pressure a pressure drop differential. A particular amount of restriction (some call it vacuum) provided by your air box keeps the internal pressure lower than atmospheric, insuring consistent fuel delivery over a wide range of temperatures and altitude. Without an acceptable pressure drop differential, the engine will be fussy about changes in jetting to maintain performance.
Another aspect that affects pressure drop is air speed (velocity). Simply put, the higher the air velocity in the carburetor, the lower the internal pressure. When you attempt to operate with a wide open air box or with the lid off, the air velocity is actually slower (yes slower) due to the enlargement of the intake opening. You now have plenty of air; however you also have poor air velocity. Velocity is needed to atomize the fuel and produce quick throttle response. This slower air speed promotes higher internal pressures, closer to atmospheric, hindering fuel delivery.

​
Click to expand...

Good read. In short your engine will run lean, lean is bad, lean equals heat, heat equals melted parts.



Advising someone to modify their factory engine now makes you the manufacturer and responsible for the outcome.
 
One bad engine Chris. Does that mod void any warranty? Got a tunnel ram on my 429 scj.....in a 1967 Ford wagon. I messed up the warranty too. Supposed to have a 428, but that 429 produces way more punch. Just thinking about it gives me a woody! This summer she's coming out again gonna give them cops some "old school" music. Tired of listening to Harleys.
 
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