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  #1   IP: 66.126.90.242
Old 07-10-2008, 12:34 PM
Kurt Kurt is offline
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Exhaust Flange and Manifold Gasket Replacement

I've been having performance issues recently manifested by loss of power/rpm in neutral and under load and slight pinging when under load. I have been racking my brain trying to figure out a solution and have done many things like new cap, rotor, plug wires, timing set, new wet exhaust. I also have a new carb on order due to a stripped out and non-functional idle mixture screw (carb threads broken). I have also noticed quick fouling of plugs. I don't think elevated exhaust back pressure due to obstruction is a problem as when motoring in neutral at 2000rpm, the water shoots 8 to 10 feet behind the boat. One thing I noticed recently is that when I was running the engine with the compartment open (companionway stairs off), my carbon monoxide detectors both had readings of at least 60 after about 10 minutes of operation - I have 2 detectors: one near the engine compartment and one all the way up in the v-berth. When the engine compartment is closed up and the blower is on the readings sit at 0. The reason this caused me concern is that when I first bought this boat 1.5 years ago, I was real paranoid about carbon monoxide fumes killing passengers sleeping in the cabin during my twice yearly 20+ hour motoring trips. So, I held one of the carbon monoxide detectors right by the exhaust flange for about 10 minutes with the engine running. The reading never got above 20. I read that anything over 30 is not good. So, I'm thinking that the only way these readings could be elevated at this point is if the flange and/or manifold gaskets are failing. I'll bet it's prudent to replace these gaskets even if this doesn't solve my performance issues. A couple questions:
1) Any thoughts on this or has anyone had carbon monoxide issues coupled with performance issues and replaced these gaskets?
2) Do you use any type of gasket sealant on these gaskets?
3) My manifold access prohibits me from using a torque wrench on the manifold nuts and I read they should be torqued to 25 lbs. Should I just make 'em tight?

Thanks for reading.
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  #2   IP: 71.2.216.33
Old 07-14-2008, 04:29 PM
GorgeSantana GorgeSantana is offline
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Back Pressure

I don't have much experience with this so take it as a possible, maybe...... When I replaced my head gasket I had most of the top of the engine off and open. It gave me a chance to pull out a bunch of gunk and clear out the passages. An amazing amount of rust chips and sediment in there. Afterwards, I flushed the engine block and water manifold.

It restarted ok but quickly started backfiring and then refused to start. When I tried to start it, smoke came out of the flame arrestor......

It was all caused by the muffler filled with debris that caused lots of back pressure. I pulled it, flushed it turned it upside down, etc. till it was clear. When I put it back on, the engine roared to life and is running well.....

Maybe you have a clogged exhaust???
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  #3   IP: 66.126.90.242
Old 07-14-2008, 05:28 PM
Kurt Kurt is offline
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Thanks for the thought, Gorge. I pulled the exhaust manifold and hot exhaust yesterday and they actually don't look bad at all - clear, no obstructions, just some carbon build up as you would expect in any exhaust. The flange gasket was totally toast so that may be why I was getting elevated carbon monoxide readings in the cabin (hopefully new gasket will solve this particularly unhealthy problem). If these items and a couple of other issues don't solve my low power problem, I'll pull the water lift muffler. That's actually the only part of the exhaust system I haven't pulled and replaced or inspected. Exhaust system overhaul - not a terrible job, but not terribly fun either!
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