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Blow By

Keeping your powerboat under power is a lot easier with good advice. Post your power systems questions here.

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tparsons56
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Joined: Tue Jan 25, 2011 8:02 am

Blow By

Post by tparsons56 » Fri Jul 03, 2020 9:39 am

I have noticed an increase in exhaust fumes in the front cockpit of my 1941 19’ Custom with M engine. I have tightened down the manifold bolts to 30#’s as per the specs. and tightened down the connection to the exhaust pipe. The smell is minimal at idle and increases with speed. Any ideas?

Greg Wallace
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Location: Indian Lake, Ohio

Re: Blow By

Post by Greg Wallace » Sun Jul 05, 2020 11:15 am

May not be exhaust, but perhaps oil fumes venting from crankcase.
Greg Wallace 23 Custom 22166 former Chris-Craft dealer Russells Point, Oh.

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matthew.smith
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Location: Reedville VA
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Re: Blow By

Post by matthew.smith » Tue Jul 07, 2020 5:13 am

Its sadly normal. I had a 19 barrel back with a M and did the same. Its annoying and can overwhelm you. Its what Greg said. Does it on my W and K as well. I have been thinking of putting in a blower. The smell is finding its way out, right under your nose
Woody Boater
1948 CC 25' Sportsman - WECATCHEM
1937 CC 16' Special Racer - Stinky
1968 Rice 40 - Trawler - Sweet Pea

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maritimeclassics
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Re: Blow By

Post by maritimeclassics » Tue Jul 07, 2020 7:42 am

You may want to check your crank case breather tube that comes off of the valve cover plate to the top of the carburetor. It should be right over the carb spark arrestor so when it sucks its taking the crank case fumes and runs them back through the engine. Also to boat should have good ventilation from the down spouts, one up front where the bow light is and it is supposed to move the air from the front to the back under the floor boards. Then exiting the boat out the rear vents. You would be surprised how many boats we see that the down spouts are missing or the owner has so much stuff packed in front of the kick board that the air can not move properly through the boat. Hope this helps.
Family member of Chris Craft founder
Owner of Maritime Classics
http://www.maritimeclassics.com
Ph# 231-486-6148

Restoration Projects:
1936 25' Gar Wood Custom
1947 Ventnor Hydroplane
1957 17' Deluxe Runabout
1948 25' Chris Craft Sportsman Twin
1959 19' Sliver Arrow Hull #75
1929 26' Chris Craft Custom Runabout
1937 25' Chris Craft Custom Runabout

tparsons56
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Joined: Tue Jan 25, 2011 8:02 am

Re: Blow By

Post by tparsons56 » Tue Jul 07, 2020 8:42 am

Thanks Mike - great suggestions. I am especially curious about the down spouts near the bow light as the fumes do seem to be coming from stern to bow from under the floor boards.

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