What Size Jets To Use In My Cv 40 Carburetor On My Harley Davidson?

How do I know what size jet carb I need?

Consult your manual first to find the stock size. Also pay attention to the numbers on the side of your old jets, which you’ll be able to see in the steps to come. A larger jet number means a bigger hole and more fuel. A smaller jet number has smaller holes and should be used if your engine needs to run more lean.

How do you know if your main jet is too big?

Typical Lean Conditions: (A too-large main jet also mimics this symptom.) – The engine runs hot, knocks, pings and overheats. – The engine surges or hunts when cruising at part-throttle. – Popping or spitting through the carb occurs when the throttle is opened.

Does main jet size affect idle?

The main jet does not effect the jetting for starting and idling. It plays no part on low RPM or mid RPM jetting either.

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What are the different jets in a carburetor?

Main Jet – this controls the fuel when you open up the throttle (between 50 and 100 percent power) Jet Needle – this controls the fuel when you open and close the throttle (between 20 and 80 percent power) Needle Jet – this is what the jet needle pops in and out of (between 15 to 60 percent of throttle.

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 you adjust air fuel mixture screws?

Turn the screw clockwise until the engine starts to sound rough.

  1. Tightening the screw weakens the air and fuel mixture and decreases the amount of fuel flowing to the engine.
  2. Tightening the screw is also called making the fuel mixture leaner, which lowers the RPMs at which the engine idles.

What does raising the needle jet do?

Raising the needle by lowering the chip position at the top of the needle will richen the mixture. Lowering the needle will lean the mixture. WIDE OPEN THROTTLE: Changing the MAIN JET affects this range. Select the size which offers the best wide open throttle.

How do you know if your pilot jet is clogged?

You should see a straight stream of fuel sprayed inside the bore or air horn. If you notice a weak stream, either the economizer and/or idle jet is partially clogged. Keep in mind that this might also be an indication of problems with the carburetor accelerator pump. Accelerate your vehicle to about 45 to 50 mph.

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What does changing the pilot jet do?

Changing the main jet size will adjust the top end of the operating range from half to full throttle. Adjusting the needle jet size, jet needle, and needle clip position will affect the mid range operation. This leaves the pilot jet size and the pilot screw for the idle and low throttle conditions.

Does needle clip affect idle?

The needle position has no affect on idle, it basically affects mixture around the 1/2 throttle range. If you need to change the WOT mixture you need to change the main jet, then change the needle to suit half throttle needs.

What jet controls idle?

The pilot jet, also called idle or slow jet, controls the amount of fuel at idle and throttle positions up to ΒΌ open.

Does pilot jet control idle?

Pilot jet controls just off idle to about mid throttle. Too rich a jet and you will load up the engine with fuel at low rpm.

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.

How do you clean carburetor jets without taking them apart?

To clean a motorcycle carburetor without removing it, you’ll need to remove the bowls at the bottom of the carburetor. Once the bowls are removed, spray some carburetor cleaner up inside, wait a few minutes, then spray again to ensure coverage. Then replace the bowls and start the motorcycle to assess how it runs.

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