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  #26   IP:
Old 10-16-2021, 10:37 PM
Dave Neptune Dave Neptune is offline
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The emulsion well is in the middle of the float bowl. The fuel from the main jet feeds fuel into it and air is fed into it via vacuum and metered by the main air (corrector) jet. The chamber has a sealing surface that must be sealed by the bowl gasket. This seal is a must for good carb performance. This feature will not leak fuel into the throat though. Look to the float and or setting for that.

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  #27   IP:
Old 10-16-2021, 10:59 PM
TimBSmith TimBSmith is offline
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Emulsion tube...and well...

This is the emulsion tube in our gravity fed system. In our system it is called the main nozzle.

Clogged emulsion tube

The fuel air mixing happens in the emulsion well into which our tube inserts and in the venturi.

An important seal is on top of the emulsion tube/nozzle (a little round gasket) and between the top and bottom of the carb. What our diagram shows as Bowl Cover Gasket. I actually put mine on inverted first attempt. Check your emulsion tube carefully because that was where my great blockages were.


From my the nozzle/emulsion tube functions...
Emulsion Immersion. You'll see references here to emulsion circuits, an important-sounding term that describes mixing fuel with air. Think of it as blowing bubbles in the fuel. All carburetors mix air with fuel in the venturi just before it enters the engine. But carburetors also mix air with fuel farther upstream inside the carburetor in the main well to make the liquid fuel easier to manage.

Last lastly really. I also remember reading and being told here to make sure the main jet gasket is seated carefully and that the main passage plug gasket is seated carefully or there can be pooling in throat from fuel pressure leak. Others can clarify. I am still learning and don't want to range to far out of my depth.
Tim Smith
Pearson 30
1974, Number 572
Boston, MA USA

Last edited by TimBSmith; 10-16-2021 at 11:10 PM. Reason: clarity.
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  #28   IP:
Old 10-17-2021, 12:24 PM
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ndutton ndutton is offline
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Maybe I missed something but reading through this thread the only issue that's been found and resolved so far is fuel pressure. Coil input voltage is still suspect as is carburetor integrity, spark and fuel quality. The burnt smell that started this off could be attributed to the fuel pump damage but with replacement of the fuel pump that's been handled. Distributor timing is low on the list because it has not been disturbed since the engine was running properly. Firing order has been mentioned more than once and is so easy to check it should have been done long before now.

So where are we?
  1. Coil input voltage @ 9 volts. Has this been resolved? What is the current input voltage?
  2. Spark quality at the time of shut down. Can you describe the spark at the plugs immediately following shutdown? Snapping blue spark or wimpy yellow? Any spark at all?
  3. Carburetor issues. We seem to be on this path now with float level concerns and gasket seal. The Moyer Marine carburetor video comes to mind.
  4. Fuel system air leaks. You reported good fuel pressure so this is also low on the list.
  5. Fuel quality. Having good fuel pressure with watered down fuel won't help. Have you tried running off an auxiliary (outboard style) fuel tank with clean, fresh fuel?
  6. Have you tried running with the fuel fill cap open?
As can be seen, we haven't even determined yet if the problem is spark or fuel related and we are how many posts into the thread, 28? Until we do all we have is guessing.
1977 Catalina 30
San Pedro, California
prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few others

Last edited by ndutton; 10-17-2021 at 12:27 PM.
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