Sooty Plugs

[roadnsky]

Carburetor float level?

Hmmm, that could be something for sure.
Joe did rebuild the carb a while back.
I remember something about the proper float level being important to control the emulsion wells and air mixture?

The exhaust had really decent flow out the transom.
Good water expelled when revving the engine too.

That leak makes me wonder what affect if any is happening.

[SubtoSail]

Jerry, thanks for the kind words. I definitely appreciate your thoughts and time, always nice to have someone to talk story with. It is reassuring to have a second opinion that overall, the engine seems to be in good shape and is not past her prime.

I feel a little silly regarding the throttle stop. Somehow I have either never noticed it, or never thought that it would be something useful to have and have never looked for it. Up until yesterday, my idling was with the throttle plate completely closed, confirmed by the control linkage on the carb. From there, I would adjust the mixture screw on the rear of the carb to get as good of a sound as I could. Based on Jerry's ears, that was probably down around 600 RPM or lower. We used the throttle stop to set the idle RPM, which clearly makes sense. By idle, I mean the spot where the throttle cable can no longer move. I think in an ideal world the engine would idle smoothly at an RPM above self sustaining with the throttle plate completely closed (no need for a throttle stop screw), but that just might not be a reality. Any thoughts or experience on setting the idle RPM with the screw on the throttle linkage?

Plugs are RJ-12C. The spares I have are a different brand, based on which ones are on the island when I buy them, but the current ones installed are RJ-12C.

The alternator belt is loose, so I will definitely tighten that up. I can check the voltage at the coil, if required.

The exhaust leak is between the manifold and the flange on the hot exhaust pipe. The leak is new and high on the fix list, only developed since removing the hot pipe in search of a blockage. I suspect I didn't scrape the old gasket completely off, and the new gasket isn't able to make a good seal.

Neil, I do have the test port in the exhaust flange, but I have not tested the back pressure. I have taken the sections apart to visually look for a blockage and found none. The water coming out of the transom batches normally, and when revving the engine it shoots rather surprisingly. The float though...

My memory of the carb assembly procedure is to screw in the float seat, drop in the needle, and put the float on. Then verify that the float is resting parallel when held upside down. My float seat is screwed all the way in. I have always screwed it completely in, checked the float, and decided it looked parallel. When I take the carb apart I'll take a picture of this step. Does the float seat normally go all the way in, or does it usually get backed out some to make the float parallel?

As for floats leaking, do you mean them filling with gas and no longer floating, or the float valve not seating? Either way, it requires a carb disassembly.

The plugs are sooty, which indicates a rich mixture. But we didn't see any other indications of a rich mixture, such as wetness on the plugs, blue exhaust smoke, or gas sheen around the exhaust port.

Thanks for all the helpful advice,
Joe

[ndutton]

Neil, I do have the test port in the exhaust flange, but I have not tested the back pressure. I have taken the sections apart to visually look for a blockage and found none. The water coming out of the transom batches normally, and when revving the engine it shoots rather surprisingly.

It's good information to know but with your exhaust volume report, probably not a priority right now.

The float though...

My memory of the carb assembly procedure is to screw in the float seat, drop in the needle, and put the float on. Then verify that the float is resting parallel when held upside down. My float seat is screwed all the way in. I have always screwed it completely in, checked the float, and decided it looked parallel. When I take the carb apart I'll take a picture of this step. Does the float seat normally go all the way in, or does it usually get backed out some to make the float parallel?

It sounds to me like you did it right.

As for floats leaking, do you mean them filling with gas and no longer floating, or the float valve not seating?

Yes and the former causes the latter. Remove the float, give it a shake next to your ear and listen for liquid sloshing around.

Please don't interpret my suggestions as derived from some mystical wisdom. I'm merely guessing as to what else might be causing your over rich mixture.

Newport 27, eh? What year? Unrelated, my step brother was a diving officer on a boomer.

[JOHN COOKSON]

Just Curious

My memory of the carb assembly procedure is to screw in the float seat, drop in the needle, and put the float on. Then verify that the float is resting parallel when held upside down. My float seat is screwed all the way in. I have always screwed it completely in, checked the float, and decided it looked parallel. When I take the carb apart I'll take a picture of this step. Does the float seat normally go all the way in, or does it usually get backed out some to make the float parallel?
Joe

What float drop measurement did you use?

TRUE GRIT

[thatch]

Just to clarify one thing, the float seat is screwed in all the way and the float adjustment is made by bending the brass hinge between the pin and the actual float.
Tom

[roadnsky]

Hey Joe-
I found this procedure that I saved from an old Dave Neptune post...

"Hold the top half of the carb upside down with no gasket and the float installed, check the height with a scale (good ruler).
The factory setting is 1 5/32" to the bottom of the float, which is on top and resting against the needle which is resting on the seat.

Two things of import here...
1-Be sure the bottom of the float is parallel with the body (this controls the closing position of the float accurately) of the carb, or as close as possible.
2-When tweaking the tabs use a pair of needle nose or duckbill pliers.
DO NOT PUSH, PULL OR BEND the tabs by holding the float itself. Only hold the brass tabs.
Now you can bend the larger portion that attaches to the float for the parallel adjustment and the little tab that rests on the seat for the height.
This can be a bit frustrating so go slow and easy.
I suggest that if anything, you set the float a bit HIGH @ 1 3/16~1 5/32.
These adjustments are important to control the emulsion wells that mix air into the fuel to break it up!
The factory adjustment specs are 1 5/32 +/_ 1/32" which is why you need it to be as parallel as possible.
I run mine at 1 7/32 and like the way it performs."


Leaving Paradise and going home today.
Always a melancholy feeling...

[JOHN COOKSON]

When setting the float drop, rather than use a ruler, try taping couple of drill bits together to use as a spacer.

TRUE GRIT

[capnward]

How does performance improve with a higher float setting? Does it accelerate quicker? Run smoother? Does it change the richness of the mixture?

[JOHN COOKSON]

How does performance improve with a higher float setting? Does it accelerate quicker? Run smoother? Does it change the richness of the mixture?

The carburetor supplies fuel mixed with the correct amount of air to the engine at all times and at all RPMs.

The float, needle valve, and seat allow the correct amount of fuel into the carburetor to accomplish this function. As fuel demands increase (RPMs increase) more fuel is allowed to enter the carburetor. There is a dynamic balance between fuel demands by the engine and the amount of fuel that enters the carburetor.

Let's start with a correctly adjusted carburetor with no fuel in it. The floats are hanging down to their max by gravity and the needle valve is open to the max. As fuel enters the carburetor the floats are lifted and the needle valve starts to close. Finally, as more fuel enters the carburetor, the floats rise even more and the needle valve is pushed all the way into it's seat closing it and allowing no more fuel to enter the carburetor.

Work these three abnormal situations through and determine how the amount fuel allowed to enter the carburetor will affect engine performance.
1. What will happen if the floats are hanging further down into the fuel bowls more than they should for correct engine operation? (to much"float drop" )
2. What will happen if the float drop is to little?
3. What will happen if there is fuel inside the floats?

TRUE GRIT

[ndutton]

Consider a straw in a soft drink cup analogy as a parallel to how your carb works.

Vacuum (more appropriately low pressure) is created in the carb bore when the piston (suction from your mouth in this analogy) drops down the cylinder drawing in a fresh intake charge. As the air is pulled through the narrower venturi and across the top of the fuel nozzle (straw), fuel (soda) is drawn up through the nozzle (straw) and enters into the airstream where it is atomized (mixed) with the air before it enters the combustion chamber. The fuel level in the bowl (level of soda in your soft drink cup) is predetermined by the float height.

Think about the difference in soda quantity with the exact same suction between a full cup of soda and a 1/4 cup and you'll see the effect float level has on mixture.

[capnward]

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.

[tac]

Don’s Explanation

https://moyermarine.com/techtip001/

[Dave Neptune]

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.

Dave Neptune

[ndutton]

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.

[capnward]

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?