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  #26   IP: 207.118.20.35
Old 08-16-2019, 01:22 AM
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Bear with me here..

OK, I understand that when the floats are adjusted to be higher above the float valve when the top of the carb is held upside down, that means they will hang deeper into the fuel chamber. (More "float drop") This means that more fuel will enter the fuel chamber before the floats close the float valve. Because the fuel chamber is fuller, the suction from the pistons will draw more gas through the nozzle at the bottom of the venturi tube, making the mixture richer. Have I got that right?
I can't say I've ever really noticed that you get more liquid to flow thru a straw in a full cup than in a 1/4 full one, with the same suction. Next time I have a straw I will experiment.
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  #27   IP: 174.242.66.173
Old 08-16-2019, 08:54 AM
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Don’s Explanation

https://moyermarine.com/techtip001/
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capnward (08-16-2019)
  #28   IP: 97.93.70.7
Old 08-16-2019, 10:03 AM
Dave Neptune Dave Neptune is offline
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Capnward, the correct float level is what the carb needs to meter properly. A "factory" carb is metered for a particular engine and this same carb can be metered different for an engine of more or less displacement and cam timing.
My job at the dyno shop was massaging carbs for modified engines. When metering orifices and emulsion wells are fed from varying fuel levels they will operate much differently. The carb we use on the A-4 is actually for a much larger engine making far more horsepower so the carb needs to be massaged as it has been to work on our A-4's. This is why a direct drive is just over half throttle and the manifold is at near zero which means it can't draw any more as that is all the 65 inches can suck and the carb is to big! If any of you have worked on a VW 40 horse just remember how small the carb was that fed it. The VW carb was at its limits at 40 HP and about 1/3 the size of our Zenith's.

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capnward (08-16-2019)
  #29   IP: 24.152.132.140
Old 08-16-2019, 10:16 AM
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Quote:
Originally Posted by capnward View Post
OK, I understand that when the floats are adjusted to be higher above the float valve when the top of the carb is held upside down, that means they will hang deeper into the fuel chamber. (More "float drop") This means that more fuel will enter the fuel chamber before the floats close the float valve
Exactly the opposite. The float setting is where you want the valve to close. Higher when upside down means lower when right side up. We set the floats upside down to ensure the valve is closed at the setting.
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Last edited by ndutton; 08-16-2019 at 10:27 AM.
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capnward (08-16-2019)
  #30   IP: 207.118.20.35
Old 08-16-2019, 10:49 AM
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Thanks Dave, it's nice to hear from the carb massager himself.
Thanks Neil, yes I just realized that myself and was about to post my correction. More float drop creates less fuel, and more air in the fuel chamber. So am I right in assuming this leans the mixture? And has the effect of reducing the size of the too-big carb? So what would be the advantages of that? Better mileage?
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  #31   IP: 71.38.107.125
Old 08-16-2019, 10:56 AM
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Originally Posted by capnward View Post
So what would be the advantages of that? Better mileage?
Yes
AND, possibly in Joe's case, less sooty plugs and a more normal setting (1.5) on the idle mixture valve
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  #32   IP: 24.152.132.140
Old 08-16-2019, 11:45 AM
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I am not advocating any change to the float setting beyond the instruction found in the MMI manual. My entire input in this thread has been to examine what might be WRONG to cause sooty plugs and an idle mixture screw setting of 2½ turns off the seat (typically 1¼~1½ turns).

While we are discussing the float setting in detail, don't forget the possibility of a leaky float affecting it's buoyancy in the carb bowl.
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  #33   IP: 71.38.107.125
Old 08-17-2019, 07:45 PM
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Hey Joe-
Can you take a voltage reading at the coil (engine running) the next time you're at the boat please?
I'd like to verify that you don't have a low voltage issue caused by your loose alternator belt.
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  #34   IP: 71.38.107.125
Old 08-17-2019, 07:49 PM
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Quote:
Originally Posted by roadnsky View Post
A few questions I have...
Would that Exhaust Leak be causing the sooty plugs?
Could that loose belt cause the ALT to put out low voltage resulting in rich running? Sooty plugs?


Thoughts?
Bumping my earlier questions to the smart guys again...
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  #35   IP: 76.173.181.116
Old Yesterday, 01:16 AM
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Some updates from my afternoon at the boat today:

Unfortunately, I didn't have time to get into the carb, so that will have to wait until next time, hopefully Thursday.

I replaced the sending line to the tachometer, and it seems to be tracking well, plus or minus about 100 RPM is my guess. I'm currently idling at about 900RPM, which might be a little fast. Using the throttle adjustment screw, not the mixture screw, I dialed it down to about 700-800, it continued to run, neutral reverse and forward. 900 sounds a lot stronger and more confident to me, so I decided to leave it there. Lower just gave me that uneasy feeling.

I did notice what I would describe as surging when at idle. It may be completely in my head, or it may be real. It sounds as if the engine is revving ever so slightly, less than 100RPM, up and down, not really in a predictable pattern. My theory on what could be causing this, other than my own paranoia, is something in the carb. Could be an obstruction somewhere, or it could be completely normal. If it's normal, my guess is that it is the engines response to the float level in the carb changing. Level drops as the motor runs, then revs slightly as the float opens and the fuel pump pumps more fuel in. Have I identified a problem here, or just learned something that is common knowledge?

The exhaust leak continues. I was able to sand the old gasket chunks off the flange, but the new gasket has deformed, likely due to the exhaust gas pushing around it, and doesn't make a good seat. Hopefully a new gasket will solve this problem.

Coil is new from MMI, and measures 4.2 ohms with nothing connected to it. Voltage at the positive post with the engine running was 14.2V, no change with change in RPM, which sounds correct to me. That yields 3.38 amps to the EI, which I believe I have read on other threads is normal, but any additional advice on that is definitely appreciated.

As for the loose alternator belt, it looks like the alternator is set as far up on the arm as possible. That means that either the belt is stretched and past its prime, or too big. I did find a presumably unused one on the boat, 25", but the cardboard it was wrapped in looks pretty old, so no harm in getting a new one. Unfortunately, I don't know which alternator I have, as there are no markings on it. I've included some pictures in the hopes someone has some experience with it. It looks pretty hefty, certainly larger than the starter.

Down to the plugs. I took updated pictures of the change I've noticed. The picture is somehow upside down, so they are one to four, right to left. They are RJ12-C, and have been in for 9 hours. I see whitening on the insulator around the center electrode, on one half of the plug. I see it on all four plugs, but more so on the more forward ones. I also notice what looks to me to be some cleaning action on the ground electrodes of 1-3, but that could be wishful thinking. I don't really know what either of these mean, if anything. Could this be an indication that whatever the soot causing condition was has cleared, and the plugs are on their way to cleaning up?

In summary:
1. Idle RPM thoughts
2. Surging
3. Any possible effects on engine performance of the exhaust leak
4. Coil voltage at 14.2V
5. Alternator assistance
6. Plug assessment

As always, thanks for your time and help!
Joe

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