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Random Quote: I'd rather be in my boat with a drink on the rocks than in the drink with my boat on the rocks!
If I am going to give my 150 merc the seafoam treatment (3/4 fuel and one bottle of seafoam), do I need to do it on the water or can I do it in the driveway with the ears on?
If you are going to soak the cylinders overnight then do it in the driveway. Remember, when you start the motor after soaking it will smoke out the neighborhood and all kind of nasty will come out of the exhaust.
You may want to make your neighbors aware of the procedure so the FD doesn't show up.
If you are just going to run seafoam through the motor in a concentrated, running it on the water may be prefferable.
__________________ USCG 100 TON MASTER
Pursuit 2870 CC
Palm Beach 161
1984 Mckee Craft 14'
Sunset on the ICW
Madeira Beach, Fl
Honeymoon Harbor
Bimini
"Many times life gives you the test, before you learn the lesson!"
I soak my cylinders about every 50 to 100 hours depending on the type of running I am doing. In the winter/spring I do alot of trolling and that tends to build up more carbon.
If you have never performed the procedure I would go with the overnight soak. It is amazing how much crud drains down through the exhaust so put a pail with under the lower unit to catch it.
You should notice a difference in the way your motor idles after the treatment.
__________________ USCG 100 TON MASTER
Pursuit 2870 CC
Palm Beach 161
1984 Mckee Craft 14'
Sunset on the ICW
Madeira Beach, Fl
Honeymoon Harbor
Bimini
"Many times life gives you the test, before you learn the lesson!"
If you are going to soak the cylinders overnight then do it in the driveway. Remember, when you start the motor after soaking it will smoke out the neighborhood and all kind of nasty will come out of the exhaust.
You may want to make your neighbors aware of the procedure so the FD doesn't show up.
Get up really early, and start it up before sunrise. There will be noise, but they will not see the smoke.
I have a Merc 200 EFI 2003 that has around 500 hours and never has had a decarb. Would it cause problems now to do this? What are the pros and cons. I don't have any problems with it now and don't want to cause any if it could cause a problem because it's never been done before.
For an outboard with alot of hours that has never been decarbed. After doing the long soak over night and running it on the muffs(And dont rev it high on the muffs) take it out on the water and do another treatment with a short soak of min 30 mins and then run it at cruise speed (4000RPM) for 5 mins. I have had better results with using the Merc Power tune then the Seafoam.. but both work..
If your location is not good to do the driveway soak, several short soaks on the water will do the trick as well..
I ran concentrate through my 150 HPDIs 15 minutes on 20 off three cycles and the smoke was visible but not outrageous. After I took it out and ran them at cruise to clean them out and one engine ran real rough for a minute while I tried to get on a plane. It eventually cleaned itself out and took off normally but I was very concerned for a minute.
You definitely want to run them after any treatment just to make sure your good to go for the next time.
A little seafoam help 
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