Talk:1980 Kawasaki KZ550-C1

fuel tap

The petcock part number 51023-1030 fits several Kawasaki models, including the KZ440 (1980-1984), KZ550 (1980-1983), ZL600 Eliminator (1986-1987, 1996-1997), KZ650H1 CSR (1981), KZ750K1 LTD (1983), and KZ750M1 CSR (1982). Additionally, it is compatible with other models such as the KZ1000, KZ1100, and KZ1300. This part is also suitable for the KZ400, KZ440, KZ550, KZ750, and KZ650.

The 1980 Kawasaki KZ550 is equipped with a vacuum-operated fuel petcock with three positions: ON, RESERVE (RES), and PRIME (PRI). Unlike manual petcocks, this vacuum-operated design does not have an explicit OFF position because it relies on engine vacuum to allow fuel flow in the ON and RES positions. When the engine is off, the petcock automatically stops fuel flow in these positions, effectively acting as an OFF state. Below is a detailed explanation of each position and the OEM part number for the petcock. Petcock Positions and Their Functions

ON:

This is the normal riding position.

Fuel flows from the main fuel pickup tube in the tank to the carburetors when the engine is running, as engine vacuum actuates a spring-loaded diaphragm in the petcock to allow fuel flow by gravity. When the engine is off, the diaphragm closes, stopping fuel flow, which eliminates the need for a manual OFF position. Use this position for regular operation when the fuel tank is sufficiently full.

RESERVE (RES):

This position allows access to the lower portion of the fuel tank (typically 0.5 to 0.7 gallons) when the main fuel supply runs low. Like the ON position, it requires engine vacuum to allow fuel flow. Switch to RES when the bike starts to sputter due to low fuel in the ON position, and refuel as soon as possible (within 10-20 miles, depending on fuel consumption).

PRIME (PRI):

The PRI position bypasses the vacuum diaphragm, allowing fuel to flow by gravity without the engine running or creating vacuum. It is typically used to fill the carburetor float bowls after the bike has been sitting for a long time (e.g., more than a few hours) or if the carburetors have been drained or run dry. Caution: Leaving the petcock in PRI when the engine is off can lead to fuel leaking into the carburetors or engine, potentially causing flooding or hydrolock. It should only be used briefly to prime the system and then switched back to ON or RES for normal operation. Some owners report using PRI to start the bike if it struggles to start in ON or RES due to low fuel levels in the carburetor bowls, but this is not always necessary if the vacuum system is functioning correctly.  Why No OFF Position?

The vacuum-operated petcock on the 1980 KZ550 is designed as an "automatic fuel tap" to prevent fuel flow when the engine is not running, reducing the risk of fuel leaks or carburetor flooding if the petcock is left on. The absence of vacuum (when the engine is off) closes the diaphragm, effectively shutting off fuel flow in the ON and RES positions. This makes a dedicated OFF position unnecessary. However, if the diaphragm or vacuum hose is damaged, fuel may leak, requiring maintenance or replacement.  OEM Part Number

The OEM part number for the fuel petcock (referred to as the "Fuel Tap" or "Valve, Fuel") for the 1980 Kawasaki KZ550 (models KZ550-A1, KZ550-C1 LTD, and others) is 51023-1039. This part is compatible with several Kawasaki models from the era, including:

• KZ550 (1980–1983)
• KZ750-H LTD (1980–1983)
• KZ1000-P Police (1982–2005)
• GPz750 (1983–1985)
• This part number is referenced in aftermarket listings and can be verified through Kawasaki parts catalogs or reputable suppliers like Z1 Enterprises or Partzilla.

 Additional Notes

Maintenance: The vacuum petcock’s diaphragm and O-rings can degrade over time, especially with modern ethanol-blended fuels (E10). This can cause leaks or failure to shut off fuel properly. Cleaning or rebuilding with a repair kit (available from Z1 Enterprises or K&L Supply) can restore functionality. Common issues include clogged strainers, cracked vacuum hoses, or a stuck diaphragm.   Vacuum Hose: Ensure the vacuum hose connected to the petcock (typically from the #3 carburetor) is in good condition, free of cracks, kinks, or leaks, as it is critical for proper operation in ON and RES positions.  Aftermarket Replacements: Some aftermarket petcocks are available (e.g., from Amazon or eBay), but compatibility issues have been reported, such as incorrect bolt spacing or levers hitting the tank. Always verify the bolt-hole spacing (typically 34mm or 44mm center-to-center) and ensure the petcock has the correct number of fuel outlets (the KZ550 typically has one fuel outlet and one vacuum port).  Manual Petcock Option: Some owners prefer replacing the vacuum petcock with a manual one (e.g., Yamaha Raptor petcock) for simplicity, but this requires manually turning the fuel off when parking to prevent leaks. Manual petcocks are not OEM for the KZ550 and may require tank modifications.  Recommendations

Normal Operation: Use the ON position for regular riding. Switch to RES when fuel runs low, and avoid leaving the petcock in PRI unless priming the carburetors. Storage: Since the ON and RES positions stop fuel flow when the engine is off, the bike can be safely parked in either position. Avoid PRI for long-term parking to prevent fuel leakage. Troubleshooting: If the bike only runs in PRI or struggles to start in ON/RES, check for:

Low fuel in the tank (ON position may not work if fuel is below the main pickup tube).

• A clogged petcock strainer or diaphragm.
• A cracked or disconnected vacuum hose.
• A faulty diaphragm in the petcock (rebuild or replace).

  Sourcing the OEM Part: Check with suppliers like Partzilla, Z1 Enterprises, or eBay for the OEM petcock (part number 51023-1039). Prices for new OEM petcocks typically range from $80–$150, though used or aftermarket options may be cheaper but less reliable.  If your 1980 Kawasaki KZ550 only runs properly in the PRIME (PRI) position when the engine is warm and fails to run in the ON or RESERVE (RES) positions, this points to an issue with the vacuum-operated fuel petcock or its related components. The PRI position bypasses the vacuum diaphragm, allowing fuel to flow by gravity, so the fact that the bike runs in PRI but struggles in ON/RES suggests a problem with the vacuum system or petcock functionality. Below are the likely causes, diagnostic steps, and solutions.

Likely Causes

Faulty Petcock Diaphragm:

The vacuum petcock relies on a spring-loaded diaphragm to open and allow fuel flow when engine vacuum is present (in ON or RES). If the diaphragm is torn, cracked, or hardened (common with age or ethanol fuel exposure), it may not open properly, restricting fuel flow when warm. Heat can exacerbate diaphragm issues, as it may cause the rubber to expand or stick, reducing fuel flow in ON/RES.

Vacuum Leak or Faulty Vacuum Hose:

The petcock requires vacuum from the #3 carburetor (typically) to actuate the diaphragm. A cracked, loose, or clogged vacuum hose can prevent sufficient vacuum from reaching the petcock, causing fuel flow to stop or become insufficient in ON/RES.

Heat may worsen a marginal vacuum leak, as hoses can become softer or less sealed when warm.

Clogged Petcock Strainer or Internal Passages:

The petcock has an internal strainer (filter) above the fuel pickup tubes for ON and RES positions. If these are clogged with debris, rust, or sediment, fuel flow may be restricted, especially when the engine demands more fuel (e.g., when warm or under load).

The PRI position bypasses these strainers, which explains why the bike runs in PRI.

Carburetor Issues Mimicking Petcock Problems:

If the carburetors have partially clogged jets or float valves, they may not draw fuel effectively in ON/RES, but the higher fuel pressure in PRI (gravity-fed) may overcome the restriction, allowing the bike to run.

Vacuum leaks at the carburetor boots or improper float levels can also cause fuel delivery issues that appear when warm.

Low Fuel Level or Tank Venting Issue:

If the fuel level is low, the ON position may not provide enough fuel, especially if the main pickup tube is partially blocked or the tank is not venting properly (e.g., clogged fuel cap vent). A clogged tank vent can create a vacuum in the tank, reducing fuel flow in ON/RES but less so in PRI due to higher flow pressure.

Diagnostic Steps

Check the Vacuum Hose:

Locate the vacuum hose running from the petcock to the #3 carburetor (usually a small-diameter hose connected to a nipple on the carb). Inspect for cracks, splits, kinks, or loose connections. Replace if damaged (use fuel-rated hose, typically 3mm or 1/8" ID). Disconnect the hose at the carburetor and apply suction (with a vacuum pump or carefully by mouth) to test if it holds vacuum. If it leaks, replace it. Ensure the vacuum port on the carburetor is not clogged.

Test the Petcock Operation:

Disconnect the fuel line from the petcock and place it in a container to catch fuel. With the petcock in ON or RES, apply suction to the vacuum port (via a vacuum pump or spare hose). Fuel should flow freely when vacuum is applied and stop when vacuum is released. If no fuel flows or flow is weak, the diaphragm or internal passages may be faulty or clogged. In PRI, fuel should flow without vacuum. If it doesn’t, the petcock’s main outlet or strainer is likely clogged.

Inspect the Petcock Strainer:

Drain the fuel tank (or ensure it’s low) and remove the petcock (two bolts, typically 34mm or 44mm spacing). Check the strainers (small filters above the ON and RES pickup tubes). Clean with carb cleaner or compressed air if clogged, or replace the petcock if damaged. Look for rust or sediment in the tank, which could be the source of clogs.

Check Tank Venting:

Open the fuel cap and see if the issue persists. If the bike runs better with the cap open, the fuel cap vent is clogged and needs cleaning or replacement. Common fix: Drill a small hole in the cap (if allowed) or clean the vent mechanism.

Inspect Carburetors:

Check for vacuum leaks at the carburetor boots (spray carb cleaner around the boots while idling; if RPM changes, there’s a leak). Verify float levels are correct (consult the KZ550 service manual, typically 22–24mm for float height). Clean jets and passages with carb cleaner or an ultrasonic cleaner, as partial clogs can cause fuel starvation that’s masked by PRI’s higher flow.

Replicate the Issue:

Run the bike until warm and the issue occurs. Switch to PRI to confirm it resolves the problem. If PRI works consistently, focus on the vacuum system or petcock. If PRI only partially helps, carburetor issues may also be involved.

Solutions

Rebuild or Replace the Petcock:

Rebuild: Purchase a petcock rebuild kit (e.g., from Z1 Enterprises or K&L Supply, ~$20–$30). These include a new diaphragm, O-rings, and gaskets. Disassemble the petcock, clean all parts, and replace worn components.

Replace: If the petcock is too damaged, replace it with an OEM unit (part number 51023-1039, ~$80–$150 from Partzilla or Z1 Enterprises). Ensure compatibility (check bolt spacing and outlet configuration). Manual Petcock Option: Some owners install a manual petcock (e.g., Yamaha Raptor petcock, ~$20) for simplicity, but this requires manually turning off fuel when parked and may need tank modifications.

Replace Vacuum Hose:

Use fuel-rated vacuum hose (3mm or 1/8" ID) to replace any damaged sections. Ensure a tight fit on both the petcock and carburetor.

Clean Fuel Tank and Petcock:

If rust or debris is present, clean the tank with a rust remover (e.g., Evapo-Rust) or vinegar and flush thoroughly. Clean the petcock strainers and passages with carb cleaner or compressed air.

Service Carburetors:

If carb issues are suspected, remove and clean the carburetors, focusing on jets, float valves, and passages. Set float levels per the manual. Replace any cracked carb boots or gaskets.

Fix Tank Venting:

Clean or replace the fuel cap if the vent is clogged. Test by riding with the cap slightly loose (for diagnostic purposes only).

Immediate Workaround

While diagnosing, you can use the PRI position to keep the bike running, but do not leave it in PRI when parked, as it can cause fuel to flood the carburetors or leak into the engine, potentially causing hydrolock or oil contamination. Switch to ON or RES when stopping, and address the issue promptly.

Recommendations

Start with the vacuum hose and petcock tests, as these are the most likely culprits given the symptoms (runs in PRI but not ON/RES). If the petcock is original (45 years old), consider replacing or rebuilding it, as rubber components degrade over time. Check for tank rust, as it’s a common issue in older bikes and can clog the petcock repeatedly. If you’re not comfortable disassembling the petcock or carburetors, consult a mechanic familiar with vintage Kawasaki bikes.