I was told by a mechanic to go ahead and trim the gasket the ics is what controls the idle speed and the only change if any should be top end mph

Was under the hatch last night and checked out the gasket. Went ahead and trimmed it. True it wont effect idle. It might change throttle position a bit a cruse speeds. Noticed fuel looked like it puddled up behind it in the elbow. This might cause some of the soot. I dont think removing it will cause a top end leanout. Be careful if you cut it in place it is a paper gasket with a metal /foil core. I can think of several reasons why the gasket is like that one is just to eliminate intake air noise at the cost of a very small amount of performance.

I'm still waiting for my mechanic to call me back. He hasn't heard from the Merc rep yet. Big surprise.

He thought it might be there to prevent gas that puddles in the elbow from getting to the flame arrester. I guess it might leak out. Why is gas puddling there in the first place with a multi-port fuel injection?

I will probably trim it too, and just keep an eye out for any gas drips from the flame arrestor.

Sorry my bad puddle was from fogging engine. I need some more sleep to many projects. Any way it dosent really cover much of the opeaning. But it would cause turbulance and a bit of air flow reversal possibly. I would like to get that elbow on my flow bench and see if filling in that area were the puddle formed would increase flow.

Im waiting to the first day I take the boat out this year, Ill make a wot run trim the gasket and make another and see if there is any change in mph

Any one run there boat yet?

Still waiting for it to warm up.

Got the boat in the water this week end. Only changes were to the throttle body gasket (trimmed it out) and changing to Redline oil in the out drive. Looked to be a lot less soot on the transom. Performance seems to be up. Some of the soot maybe from fogging oil burining off. No full throttle runs yet had it up to an easy 60 for a few. Mid range seems a bit better dont expect to see top end gains with the rpm limiter and not changeing the prop

I trimmed the gasket and ran it last weekend but the water was too rough to do top speed runs.

A loud whistling sound is present now when the throttle blade starts to open and when running between 2200 and about 3200 RPM. Any of you guys that trimmed your gaskets get that now? I wonder if that's why Mercruiser has the gasket shaped that way. I have to decide if it bothers me too much. I'll get a new one and put it in again if it starts annoying the crap out of me.

Yes I got the whistle too. Some manifolds I have designed "fingers"were incorperated in the design to reduce harmonics but the boat seems more responsive in mid range. Also have added a Jacobs omni with restrike not enough testing yet but it seems to have helped alot too.