This was my first year with my newly acquired 1968 Commander, 35' twin 327f.

The engines start and run fantastic. I get a lot of fumes when under way. We have tried having the hatch in the front open when under way. We have tried the hatch and cabin windows open. We have tried having nothing open.

I had the boat pulled for the season this past week (sad day) and cleaned the boat out for winter storage. The clothing stored in the boat since the launch in July smell of exhaust fumes so strong you would not want to wear them.

My guess is the engines are running rich but I though maybe everyone has this issue.

Opinions please.

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I also own a 1968 35 and experienced this same problem.
In my first summer (2017) .
I had read about Tims great idea about the tennis balls in the aft drains.I ofcourse went and got some tennis balls right away and tried them out.
Unfortunately they did not seem to make a difference

After last season I began a pretty sizeable overhaul of my boats engine compartment.
After I removed the engines, the remainder of the tired old exhaust system when I found the root of my exhaust problem with 100% certainty.

So from the engines our boats have collectors which take the dual exhaust from the engines into a single pipe.(in my case with the 427s the collector takes the engines two 3.5" outlets into one 4.5"pipe) From there, there's a 90° (4.5") elbow that direct the exhaust towards the silencers. Just fown stream of this elbow there is a straight section of copper pipe. However this pipe is a 4" od as is the silencer and the tips on the transom.
I can only assume this was done because Chris Craft likely had tons of 4" silencers and it was less expensive to reduce the size of their exhaust than to cast 4.5"
Silencers.

Anyway, this reduction in the exhaust happens on the upstream side of the straight coper pipe which is between the gas tanks and the hull sides. There is a steel doughnut that was brazed to the copper pipe to allow a 4.5" id hose to connect to it.
Well 49 years of use had taken its toll on the steel week link.
It had rusted thru and caused my exhaust leak.

At slower speeds I belive the water passing over the hole in the reducer auctually somewhat kept the exhaust gasses from leaking out but at cruise when water was rushing thru the reducer it alowed gasses to escape into the bilge.

Additionally my cast ironsilencers also had small holes that developed in their bottoms.
Furthermore two of the short boses that connected pipe to pipe had drird up and were also contributing to my exhaust leaks.

Please excuse the typos in my above response. For some reason the edit feature is not alowing me to save corrections. 

Anyway heres a few photos of the exhaust issues I found

Attachments:

An update to what I changed and found this year.

Earlier this season I noticed one of my engines would not easily get to over 3700 RPMs while under load. It is not often that I push them that hard. 

So although the engines both started within seconds of turning the key and would idle thru no-wake zones "all-day", one engine was still not operating as it was capable.  I installed new spark plugs and the issue was resolved, AND the fumes were greatly reduced.  

I also used the tennis ball suggestion and I run the bilge exhaust fan for a long time (at least 15 minutes) after shutting the engines off.  All of these things have helped.

Thanks for all the input.

Steve

is this a salt water or fresh water boat?



Jeremy Goldstein said:

I also own a 1968 35 and experienced this same problem.
In my first summer (2017) .
I had read about Tims great idea about the tennis balls in the aft drains.I ofcourse went and got some tennis balls right away and tried them out.
Unfortunately they did not seem to make a difference

After last season I began a pretty sizeable overhaul of my boats engine compartment.
After I removed the engines, the remainder of the tired old exhaust system when I found the root of my exhaust problem with 100% certainty.

So from the engines our boats have collectors which take the dual exhaust from the engines into a single pipe.(in my case with the 427s the collector takes the engines two 3.5" outlets into one 4.5"pipe) From there, there's a 90° (4.5") elbow that direct the exhaust towards the silencers. Just fown stream of this elbow there is a straight section of copper pipe. However this pipe is a 4" od as is the silencer and the tips on the transom.
I can only assume this was done because Chris Craft likely had tons of 4" silencers and it was less expensive to reduce the size of their exhaust than to cast 4.5"
Silencers.

Anyway, this reduction in the exhaust happens on the upstream side of the straight coper pipe which is between the gas tanks and the hull sides. There is a steel doughnut that was brazed to the copper pipe to allow a 4.5" id hose to connect to it.
Well 49 years of use had taken its toll on the steel week link.
It had rusted thru and caused my exhaust leak.

At slower speeds I belive the water passing over the hole in the reducer auctually somewhat kept the exhaust gasses from leaking out but at cruise when water was rushing thru the reducer it alowed gasses to escape into the bilge.

Additionally my cast ironsilencers also had small holes that developed in their bottoms.
Furthermore two of the short boses that connected pipe to pipe had drird up and were also contributing to my exhaust leaks.

Freah

glenn woudenberg said:

is this a salt water or fresh water boat?



Jeremy Goldstein said:

I also own a 1968 35 and experienced this same problem.
In my first summer (2017) .
I had read about Tims great idea about the tennis balls in the aft drains.I ofcourse went and got some tennis balls right away and tried them out.
Unfortunately they did not seem to make a difference

After last season I began a pretty sizeable overhaul of my boats engine compartment.
After I removed the engines, the remainder of the tired old exhaust system when I found the root of my exhaust problem with 100% certainty.

So from the engines our boats have collectors which take the dual exhaust from the engines into a single pipe.(in my case with the 427s the collector takes the engines two 3.5" outlets into one 4.5"pipe) From there, there's a 90° (4.5") elbow that direct the exhaust towards the silencers. Just fown stream of this elbow there is a straight section of copper pipe. However this pipe is a 4" od as is the silencer and the tips on the transom.
I can only assume this was done because Chris Craft likely had tons of 4" silencers and it was less expensive to reduce the size of their exhaust than to cast 4.5"
Silencers.

Anyway, this reduction in the exhaust happens on the upstream side of the straight coper pipe which is between the gas tanks and the hull sides. There is a steel doughnut that was brazed to the copper pipe to allow a 4.5" id hose to connect to it.
Well 49 years of use had taken its toll on the steel week link.
It had rusted thru and caused my exhaust leak.

At slower speeds I belive the water passing over the hole in the reducer auctually somewhat kept the exhaust gasses from leaking out but at cruise when water was rushing thru the reducer it alowed gasses to escape into the bilge.

Additionally my cast ironsilencers also had small holes that developed in their bottoms.
Furthermore two of the short boses that connected pipe to pipe had drird up and were also contributing to my exhaust leaks.

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