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  #26   IP:
Old 03-15-2017, 03:59 PM
macgyro macgyro is offline
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Similar symptoms, no exhaust blockage

Hi guys,

I know this thread has been inactive for a while, but the symptoms described were exactly what I was experiencing at the end of last season. My RPM wouldn't go above 1800 RPM and it sounded like the engine was flooding/bogging down. It started funny, sometimes with no choke, sometimes it wouldn't run without choke, but never ran quite right.

I tried different twists of the mixture control jet screw thing on the aft end of the carb, different choke settings, etc. Then I pulled the plugs, and the forward 3 were black and sooty with the aft-most slightly white.

I found this thread and, the next day, removed my exhaust hoses to try to find the blockage. All of the hoses were fine, so I blew into the muffler and launched a fountain of glycol all over the cockpit of the boat. Then I removed the dry exhaust section from the manifold. No blockages anywhere, including the thru-hull on the transom (Ericson 32).

Could the exhaust blockage be in the manifold?

Part 2:
Early last season, the engine started to overheat (200 degrees) and I installed the cooling bypass line with the shutoff valve and used it with the bypass valve mostly closed. Then, the engine ran too cool and would rarely get up to temperature but was still running fine (up to about 2200 RPM on my tach. I don't think the tach is set right) I was nervous about running for a long time with the valve completely open in case I forgot to monitor the temperature and it climbed again. I got a new thermostat this winter, so I'm hoping to keep the valve open and it will work.

That was a long story, but since I ran the engine for most of the season too cool, I'm wondering if that could have fouled the plugs enough alone to cause my symptoms without excessive exhaust backpressure?

If anyone's still out there, do you have any ideas?


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  #27   IP:
Old 03-16-2017, 11:07 AM
Dave Neptune Dave Neptune is online now
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Dean, I suggest a new thread. It sounds like one of two things or possibly both. First the idle screw will only affect the idle circuit and it sounds like the carb is running way rich to cause sooty plugs. A good look at the carb is in order and a thorough cleaning.
Second is timing. Timing can be way off if the points (if still equipped with them) and the cam are worn down a likely senarior due to the age of the motor. Check the "dwell" not the gap in these old engines!!!! Be sure you have a good "blue" spark and set the timing or just try a bit of "advance" to see if it helps.
The right fuel mix (carb)~good blue spark~and the spark being delivered at the right time (timing) equals a good running engine!!
Other notes connected to the above. Make sure the centrifugal advance is working inside the distributor~ a fresh cap and rotor~fresh plugs~plug wires in good shape. Also do a visual to be sure the choke is fully opening and closing.
I don't see how the manifold itself could create a blockage inside.

Dave Neptune
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  #28   IP:
Old 11-24-2020, 09:40 AM
wakemutant wakemutant is offline
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How does one inspect the various pipes in the exhaust line to ensure no obstructions? I have a good old stand pipe muffler with the coolling water ejection BRAIDED LINE (8 PLY) SEA STORM - MZBL8YW-XXX at the top of the standing system as is common. Should I just start yanking things apart? What should I be looking for?

Last edited by wakemutant; 12-04-2020 at 04:47 AM.
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  #29   IP:
Old 11-24-2020, 10:04 AM
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ndutton ndutton is offline
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Originally Posted by wakemutant View Post
How does one inspect the various pipes in the exhaust line to ensure no obstructions?
Exhaust back pressure gauge.
1977 Catalina 30
San Pedro, California
prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few others
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