Priming, Choking, and Enriching
By: John Ratliff, AKA "Rat"

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Priming is a word that can mean several different things. Priming really means injecting fuel into the intake system. Now, for the engine to actually run you must have the fuel bowl full. How do you get the fuel bowls full? You prime them. That's where the word gets confused. You are not priming the engine in this case, only priming the fuel bowl in order to fill it up. The factory supplies a rubber squeeze bulb to do this, but some find the rubber squeeze bulb eventually malfunctions, so they don't use it.

That's where the Facet fuel pump comes in. When you turn on the Facet it pushes fuel into the float bowls to fill them up. It will also keep them full in flight if the Mikuni were to stop pumping. So, you have to "prime" the float bowls to fill them up, but to start a cold engine you need extra fuel going into the intake system. Either the primer or enricher circuit will do that for you.

The enricher circuit has a small pipe that goes down into the fuel in the float bowl. Normally the enricher is closed. There is a strong spring that holds the enricher piston down over that pipe so nothing can flow up it into the carb. When you activate the enricher you lift that spring-loaded plunger, allowing fuel to be pulled directly into the intake. It doesn't have anything to do with carb jets; it's a separate circuit that will pull fuel up into the carb throat thru the enricher pipe as the engine is turned over by rope start or electric start. It is important to note that the throttle must be closed in order for the engine to form a vacuum strong enough to pull the fuel through the enricher circuit.

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Why it's not a “choke”. The enricher circuit on the Bing carb is pretty clever but by definition it's not a “choke”. A choke device is normally located at the very outer portion of the carb intake. Sometimes it is a butterfly valve that is rotated to close off (or choke) the intake system, sometimes just a flat slide is used to move down over the intake system. The flat slide type is common on small engines such as chain saws, for instance. In either case, the choke closes off most of the intake system. So when the engine is turned over to start it, the choke valve blocks the suction from the intake and that causes extra "rich" fuel to be pulled up through the normal main jet. It is enriching the fuel mixture that way, but is called a choke. Since Bing doesn't use an actual choke, they call their circuit an enricher. Some may call it a choke though not technically correct, probably because Bing labeled the enricher levers “choke”. No matter if you call it an enricher or choke, on the Bing 54 that we use, it has the same effect.

There is no primer included with the kit to prime the carbs, but there is a spot on the carb where a primer can be connected. There is a small fitting on the side of the carb with a rubber cap over it that's the primer port. If you were to squirt some fuel into that port it would go directly into the intake and be ready to be pulled into the engine as you start it. Sometimes, especially in cold weather, the enricher isn't delivering enough extra fuel into the carb throat for the engine to start easily. The rubber cap is removed, a piece of fuel line is attached there, and fuel is injected directly into the carb. If you inject too much fuel that way, you will flood the engine and it won't start anyway. Either not enough fuel, or too much fuel, and the engine will not start and run.

If you want even more fuel in the intake, prior to turning the engine over, you need to squirt a shot of "prime" directly into the intake. Bing has given us that option by providing the rubber-capped primer port.

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The mechanical primer is really just a small hand operated fuel pump, mini-sized. A fuel line from the tank goes to the intake side of the primer pump and a fuel line from that pump goes to the primer port on the side of the carb. You pull-push the primer pump and it causes fuel to be pulled from the tank and then squirted directly into the carb throat. Depending on where you install this pump, you may have raw fuel lines running all the way up to the front of the cockpit. Not a great idea, even on Cessna, which normally has a pull-push primer pump on the dash. The pump may eventually start to leak when being used and raw gas can then drip into the cockpit.


The same thing can be accomplished with the use of a primer solenoid. A fuel line goes from a T-fitting in the fuel line, after the Facet pump directly to the primer solenoid, which is normally closed to the primer port. You turn on the Facet pump, which pressurizes the fuel line, then activate an electric switch, which momentarily opens the primer solenoid allowing fuel to squirt into the primer port. The difference here is that all the plumbing for this is back at the fuel tank, with no fuel lines running up front like a mechanical pump requires.

If the enricher circuit is working correctly, the float bowl is full, and the carb slide is all the way down, you should be able to start the engine without any additional raw gas "prime" being shot into the intake. In cold conditions a shot of prime would be helpful, but in most cases the Bing will function just fine with only the standard enricher circuit used for starting the engine.

Lastly, since the Bing enricher circuit outlet is located behind the front face of the carb slide, it works best for starting if the carb slide is down as far as it can go. Simply put, more suction is developed to pull fuel thru the enricher passage that way. The engine idle speed is set by how far up the carb slide is positioned. With a very fast idle the carb slide is raised up more than with a slow idle. In that case the enricher circuit may still work, but not as aggressively.

We suggest you add one more manual to your library. There is a very nice one that has a lot of information about your Bing carb. Just go to Bing International L.L.C., use their 1-800-309-2464 number, and order one for only $8.95 postpaid.

More information on fuel systems and how to install the components can be found on our Fuel Systems page.