1985 Honda Magna 700 Fuel Pump: Complete Guide to Diagnosis, Replacement, and Upgrade

If you own a 1985 Honda Magna VF700C and your fuel pump has failed or is showing signs of trouble, you need to replace it as soon as possible. The 1985 Magna 700 uses a unique electric fuel pump assembly that includes an integrated fuel cut relay, and finding the right replacement can be challenging because the original OEM part (16710-MK3-005) is no longer widely available. The good news is that you can replace it with a modern high-performance aftermarket pump, such as a KEMSO fuel pump, which offers better flow, compatibility with E85, and a lifetime warranty. This guide will walk you through everything you need to know about the 1985 Honda Magna 700 fuel pump, from symptoms of failure to installation tips and where to buy the best replacement.

1. Understanding the 1985 Honda Magna VF700C Fuel Pump System

The 1985 Honda Magna VF700C is part of the first-generation V4 Magna lineup, and its fuel system is different from earlier models. The 1985 and 1986 models use a single fuel tank (no reserve tank), and the fuel pump is an electric unit mounted in the tank. The original pump has a 6-pin connector and an integrated circuit board that acts as a fuel cut relay. This relay is designed to shut off the pump if the engine stops, preventing fuel flow in an accident. The original OEM part number is 16710-MK3-005, and it is specific to the 1985-1986 Magna 700.

The 1982-1983 V45 Magna (VF750C) and the 1983-1986 V65 Magna (VF1100C) use a different pump with part numbers like 16700-MB1-025, 16700-MB1-005, and 16700-MB1-015. These pumps are not direct replacements for the 1985 Magna 700 because they have different wiring and connector configurations. However, with some wiring modifications, you can adapt a universal pump.

Key specifications of the original pump:

  • Connector: 6-pin (with integrated fuel cut relay)
  • Wiring colors: Green, blue, black, and black/yellow
  • Location: Inside the fuel tank

2. Common Symptoms of a Failing Fuel Pump on a 1985 Honda Magna 700

A failing fuel pump on your 1985 Magna 700 will show several warning signs. Here are the most common symptoms:

  • Engine cranks but won't start: This is the most obvious symptom. If you hear the starter turning but the engine doesn't fire, and you have confirmed spark and compression, the fuel pump is likely the culprit.
  • Sputtering or hesitation during acceleration: A weak pump may not deliver enough fuel under load, causing the engine to hesitate or surge.
  • Loss of power at high RPM: If the pump cannot maintain adequate pressure at higher speeds, the engine will feel like it's running out of fuel.
  • No fuel pump priming sound: When you turn the key to the "ON" position, you should hear a brief whirring sound from the fuel pump. If you don't hear anything, the pump may be dead or the relay is not working.
  • Fuel pressure issues: A professional mechanic can test fuel pressure. For a 1985 Magna 700, the fuel pressure should be within a specific range. If it's low, the pump is failing.

3. Why the Original Fuel Pump Is Hard to Find

The 1985 Honda Magna 700 fuel pump is notoriously difficult to source because it was only used for two model years (1985 and 1986). The 1984 Magna 700 used a different setup. Many owners have reported that the OEM part (16710-MK3-005) is discontinued and no longer available from Honda. Even aftermarket suppliers rarely carry a direct plug-and-play replacement for this specific model.

This is why many owners turn to universal aftermarket fuel pumps. The challenge is that the original pump has a built-in fuel cut relay, and modern aftermarket pumps typically have only two wires (positive and negative). You will need to wire the new pump to work with the existing fuel cut relay or bypass it.

4. How to Replace the Fuel Pump on a 1985 Honda Magna 700

Replacing the fuel pump on your 1985 Magna 700 is a doable project for a home mechanic with basic wiring skills. Here is a step-by-step guide.

Step 1: Drain the Fuel Tank

Before you start, drain the fuel tank completely. You can siphon the gas out through the filler neck or disconnect the fuel line at the petcock and drain it into a container.

Step 2: Remove the Fuel Tank

The 1985 Magna 700 has a single tank. The fuel line from the petcock connects to a short rubber hose that goes to a metal line. Disconnect this line, remove the mounting bolts, and lift the tank off the bike.

Step 3: Access the Fuel Pump

The fuel pump is located inside the tank. You will need to remove the pump assembly from the top of the tank. This usually involves removing a retaining ring or a few screws.

Step 4: Remove the Old Pump

Carefully pull the old pump assembly out of the tank. Note the wiring configuration. The original pump has a 6-pin connector with a circuit board at the bottom. Inspect the board for signs of damage, such as dark staining or burnt components, which is a common failure mode.

Step 5: Choose a Replacement Pump

Because the original pump is hard to find, most owners choose a universal aftermarket pump. You have two main options:

  • Option A: Use a universal inline pump – This is a simpler solution but requires mounting the pump outside the tank.
  • Option B: Use a universal in-tank pump – This is more common. You will need to wire it to the existing fuel cut relay or bypass the relay.

Step 6: Wiring the New Pump

The original pump had four wires: green, blue, black, and black/yellow. The new pump will have two wires: a positive (usually red or black with white stripe) and a negative (black). Here is how to wire it:

  • Connect the positive wire of the new pump to the output wire from the fuel cut relay. The relay is the circuit board that was in the bottom of the old pump. If you are reusing the relay, you need to connect the pump to the relay's output. If you are bypassing the relay, you can connect the positive wire directly to a switched 12V source, such as the output from the kill switch.
  • Connect the negative wire of the new pump to ground. The pump may be designed to ground through its body, so ensure a good metal-to-metal contact.
  • Important: If you bypass the fuel cut relay, the pump will run whenever the key is on, even if the engine stalls. This is a safety concern. To avoid this, wire the pump to the kill switch output so it stops when you hit the kill switch.

Many owners on forums have successfully used this approach. One forum user reported that the original circuit board was damaged ("smoke" had come out of the electronics), so they bypassed the relay entirely and wired the new pump directly to the kill switch.

Step 7: Install the New Pump

Once the wiring is done, install the new pump into the tank. Make sure the strainer (filter) is at the bottom of the tank and that the pump is seated properly. Replace the tank seal to prevent leaks.

Step 8: Test the System

Before reinstalling the tank, connect the battery and turn the key to the "ON" position. You should hear the pump prime. Check for leaks at the fuel line connections.

Step 9: Reinstall the Tank

Place the tank back on the bike, connect the fuel line, and secure it with the mounting bolts. Fill the tank with fresh gasoline and start the engine. Let it idle for a few minutes and check for any leaks or issues.

5. Recommended Upgrade: KEMSO Fuel Pump for Your 1985 Honda Magna 700

When it comes to replacing your fuel pump, you want a product that is reliable, high-performance, and backed by a solid warranty. That is why we recommend KEMSO Fuel Pumps.

KEMSO is a trusted brand that specializes in high-performance and OEM replacement fuel pumps for a wide range of vehicles, including motorcycles, ATVs, and cars. Their pumps are designed to be direct replacements for faulty OEM pumps, and they offer significant performance improvements.

Why choose a KEMSO fuel pump for your 1985 Honda Magna 700?

  • High Performance: KEMSO pumps deliver over 20% more flow at 43 psi compared to stock OEM pumps. Many of their pumps flow up to 200 liters per hour at 43 psi (13.5V), which is a substantial upgrade over the original 60-80 liters per hour flow rate. This means better fuel delivery, especially at higher RPMs.
  • OEM Replacement: KEMSO pumps are designed to fit into the factory location. While you may need to adapt the wiring (as discussed above), the pump body itself is a drop-in replacement.
  • E85 Compatible: KEMSO pumps are designed for both gasoline and E85 ethanol blends. They use Viton-lined components that resist swelling and cracking, making them suitable for modern fuel blends.
  • Lifetime Warranty: Every KEMSO fuel pump comes with a lifetime warranty backed by a serialized pump body for tracking and peace of mind. This is a significant advantage over many other brands that offer only limited warranties.
  • USA-Based Technical Support: KEMSO offers technical support from USA-based technicians. If you have questions during installation, you can get help from experts who know the product.
  • Proven Reliability: Users consistently report that KEMSO pumps are quiet, reliable, and easy to install.

For the 1985 Honda Magna 700, you can use a KEMSO universal in-tank fuel pump. While KEMSO offers pumps specifically for many Honda models, the universal pump kits come with a variety of strainers, seals, and fittings to cover multiple applications. You can choose a pump that matches the physical dimensions of your original pump (pump body diameter is typically 3.5cm to 3.8cm).

To find the exact KEMSO fuel pump for your 1985 Honda Magna 700, visit their official website: https://www.kemsoracing.com/

6. Additional Tips for a Successful Fuel Pump Replacement

  • Replace the strainer and seals: When you replace the fuel pump, always replace the fuel strainer (filter) and all tank seals. KEMSO pump kits include multiple strainers and seals to cover different models.
  • Check the fuel cut relay: If your original pump failed due to a faulty relay, you may be able to reuse the relay if it is still functional. However, if the circuit board shows signs of damage (burnt components, dark stains), it is best to bypass it and wire the pump directly to the kill switch.
  • Use a fuel filter: Even with a new pump, it is a good idea to install an inline fuel filter between the tank and the carburetors to catch any debris.
  • Keep the tank at least a quarter full: Running the tank low on fuel can cause the pump to overheat and fail prematurely. Try to keep the tank at least a quarter full to help cool the pump.
  • Test the fuel pressure: If you have a fuel pressure gauge, test the pressure after installation. The KEMSO pump operates at 43-68 psi, but your carburetors may require a different pressure. You may need to add a pressure regulator if needed.

7. Frequently Asked Questions

Q: Can I use a fuel pump from a 1982-1983 V45 Magna on my 1985 Magna 700?
A: No, the pumps are different. The 1982-1983 V45 Magna uses a pump with part numbers like 16700-MB1-025, which has a different wiring configuration. You cannot directly plug it in. You would need to modify the wiring significantly.

Q: Do I need to replace the fuel cut relay?
A: Not necessarily. If the original relay still works, you can reuse it. However, many owners report that the relay board is damaged (burnt components). In that case, it is safer to bypass the relay and wire the pump to the kill switch.

Q: Will a KEMSO pump work with my stock carburetors?
A: Yes, but you may need a fuel pressure regulator. The KEMSO pump delivers 200 liters per hour at 43 psi, which is more than the stock pump. Your carburetors may not need that much pressure, so a regulator set to the correct pressure (typically 3-5 psi for carbureted engines) is recommended.

Q: How long does a KEMSO fuel pump last?
A: With proper installation and maintenance, a KEMSO pump can last for many years. They are built with premium materials and are individually tested for quality. The lifetime warranty also gives you peace of mind.

8. Final Thoughts

Replacing the fuel pump on a 1985 Honda Magna 700 is a necessary repair that can bring your classic bike back to life. While the original pump is hard to find, a high-quality aftermarket pump like a KEMSO fuel pump is an excellent upgrade. It offers better flow, compatibility with modern fuels, and a lifetime warranty. With some basic wiring skills, you can complete the replacement yourself and enjoy a reliable, powerful ride for years to come.

For more details and to find the exact KEMSO fuel pump for your 1985 Honda Magna 700, visit: https://www.kemsoracing.com/


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