Question: What Are Stock Jets Size Main And Low For 1985 Harley-davidson Fxrt Keihin Butterfly Carburetor?

How do you tell what size a carb jet is?

Jets are threaded and have a small orifice through their center that varies based on the size of the jet. For example, a jet may be stamped (on its head) with the number 30. This indicates that the jet’s size is 30 mm.

How do you measure a pilot jet?

The pilot jet is sized correctly if the fuel screw setting falls between 2.5-3 turns out. The pilot jet is sized correctly if the air screw setting falls between 1-2 turns out, with 1.5 being the sweet spot.

What do carb jet numbers mean?

For Keihin Carbs the jet sizes refer to the metering orifice diameter, expressed in millimeters. A # 100 jet is 1.00mm in diiameter. A # 38 Jet is 0.38 mm in diameter. A #35 jet is 0.35mm in diameter.

Where is the main jet on a Keihin carburetor?

The main jet affects the jetting in the upper quarter of the throttle position. Coming into play at ¾ throttle on through to wide open throttle. Even though most people relate the main jet to their carburetor in general, the main jet is only responsible for the last ¼ of the jetting.

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What happens if main jet is too big?

For example, using too large of a main jet will cause more fuel to enter the combustion chamber than it can efficiently burn. This will result in a “sputter” at full throttle. It could best be described as a rapid misfire.

What happens if main jet is too small?

Be careful: most engine jams occur when the main jet is too small. A lean fuel/air mixture will cause the engine to overheat fast.

How do I know if my pilot jet is too rich?

If the pilot circuit is rich, the engine will have a rough idle or may not return to idle without “blipping” the throttle. You may also notice a distinct smell of raw fuel and some eye irritation from the exhaust.

What is the pilot jet in a carburetor?

The pilot jet handles the mixture from idle to 15 to 20 percent throttle. Air comes in through the front of the carburetor drawing fuel up through the pilot with a vacuum that is created as the air flows through the pilot circuit.

What is the pilot screw on a carburetor?

The pilot air screw and pilot jet. The air screw can be located either near the back side of the carburetor or near the front of the carburetor. If the screw is located near the back, it regulates how much air enters the circuit. If the screw is turned in, it reduces the amount of air and richens the mixture.

How do I know if I need to Rejet my carb?

A clean spark plug means you can skip the rejet. A black, sooty-looking spark plug means you’re running rich with too much fuel in your mix. If you see white residue, that means you’re running lean with too much air. In both cases, you need a rejet.

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Can you drill out carb jets?

By drilling out your stock main jet to larger sizes you will be able to narrow down what jet size your carburetor needs. You will need a numbered drill bit set. If it’s lean and you need to increase the size of your main jet, drill the jet out with the next size larger drill bit, which in this case is the #60 bit.

Does jet size affect idle?

As far as jetting goes, the jet size will not affect idle, as the jets don’t come into play until the carb transitions to the primary circuit, unless the throttle blades are open far enough to expose the transfer slot.

Are all Keihin carb jets the same?

Yes, the jets are interchangable, IF it is the same series of carb. Scroll down to the blue links and find the carb that matches your carb.

How do I identify my Keihin carburetor?

Find the serial number near the bottom of the CDK carburetor. Write the number down. Call one of the distributors listed on the keihin-us.com website and give them your serial number. Distributors keep track of serial numbers and will be able to identify your particular carburetor.

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