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Old 06-23-2010, 03:28 PM   #1
Lt. JG
Join Date: Apr 2009
Location: Loch Lomond Scotland
Posts: 31
Default Intake Air Control Muffler sucked into Mag 350 MPI

Was out last night and noticed a rather loud sucking noise from engine, headed out of marina and tried to get onto plane struggled to get above 3500rpm

On removing the flame arrestor and cover i noticed the little muffler for the air control valve is missing and i suspect this is what is causing the sucking sound but i have a few questions

1) If this has come loose and been sucked down into the air manifolds where will this muffler end up?????

2) Depending where it ends up what will it do, block something, get incinerated and fired out exhaust??????

3) Is it the muffler being missing that caused the lack of power to get onto the plane or the fact the muffler is missing and stuck somewhere???

Oh and to throw the cat among the pigeons this sucking noicse has actually been about for 2 or 3 trips now and i have managed to get onto the plane and go up the revs ok, also the other night i actually go onto the plane and was up at 4100rpm before i reduced throttle and came of plane its when i tried to get her back on that lack of power appeared

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Old 06-23-2010, 04:17 PM   #2

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it sounds like it's moving around in the intake manifold somewhere...if it's been dropped off it's mounting then you need to find it before it does some damage...and will cause some serious damage to a piston and/or it won't shoot out the exhaust unless it's in pieces....


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Old 06-24-2010, 10:00 AM   #3
Lt. JG
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Location: Loch Lomond Scotland
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Hi SP Cheers for response although not sure we are talking about same part here

This is a little piece approx 3/4" square bit of sponge, i'd call it a filter American websites sites call it a muffler, its a $1.50 piece of soft material so not going to do any damage to pistons or valves.

The air valve which is near the air intake chamber has a hose from it onto the intake chamber (I'm calling the intake chamber the part that the flame arrestor mounts onto), when you remove the flame arrestor and look at the big butterfly valve north of this is where this little bit of sponge sits

Actually just attached photo of this showing white/black muffler in place
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Old 06-24-2010, 10:14 AM   #4
Lt. JG
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Old 06-24-2010, 01:43 PM   #5

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The photo is a little too close so I'm not quite certain what I'm looking at. My boat has a 350 MAG MPI as well but I've not had the flame arrestor off so I'm unfamiliar with the set up.

Regardless, if the muffler did come loose and was ingested by the engine it would have been drawn into one of the intake manifold runners. Given it's size I think it unlikely that it could have gotten past the intake valve (which, on this engine, opens less than 1/2 inch). It is very possible, though, that the muffler is caught between the intake valve and the valve seat, preventing the intake valve from closing, thereby resulting in a mis-fire in that cylinder. If you notice the engine running badly, or hear a miss, you'll know where the muffler ended up. This is bad because it could burn a valve.

If you are convinced the muffler is in the engine you'd better take steps to find it. Remove the throttle body from the intake manifold and use a borescope to look in each intale manifold runner.

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