John Deere 318 Fuel Pump: Everything You Need to Know for a Reliable Repair
If you own a John Deere 318 garden tractor, the most common issue you will face is a failing fuel pump. The fuel pump is a critical component that delivers gasoline from the tank to the carburetor, and when it stops working, your engine will not start or will run poorly. The good news is that replacing or rebuilding the fuel pump on a John Deere 318 is a straightforward job that you can do yourself with basic tools. In this guide, I will walk you through the symptoms of a bad pump, how to test it, which replacement parts to buy, and step-by-step installation instructions. By the end, you will be able to fix your tractor quickly and save money on mechanic fees.
Understanding the John Deere 318 Fuel System
The John Deere 318 was built from 1984 to 1992 and came with either the Onan P218G or the Kawasaki FD590V engine. Both engines use a mechanical fuel pump that is operated by a pushrod from the camshaft. The pump has three ports: an inlet from the fuel tank, an outlet to the carburetor, and a vent line that opens to the atmosphere. The pump works by creating vacuum pressure to pull fuel and then pushing it to the carburetor under positive pressure.
This mechanical design is simple and reliable, but over time the rubber diaphragm inside the pump can crack, harden, or develop a leak. When that happens, you will notice specific problems. The pump is located on the side of the engine block, usually near the oil filter or behind the shroud. It is held by two bolts and connected by rubber hoses and often a metal line.
Because the pump is mechanical, there is no electrical failure to worry about, but the pushrod can also wear out. The pushrod is a small metal rod that transfers motion from the camshaft to the pump. If your pushrod is worn, the pump will not get full travel and will not pump enough fuel. So when troubleshooting a fuel delivery problem, always check the pump and the pushrod together.
Common Symptoms of a Bad Fuel Pump
A failing fuel pump on a John Deere 318 will show clear warning signs. Do not ignore these symptoms, as running the tractor with a bad pump can cause engine damage from lean fuel mixture.
1. Engine cranks but will not start. This is the most obvious sign. If you have spark and compression, but the engine gets no fuel, the pump is likely dead. You can test this by disconnecting the fuel line from the carburetor and cranking the engine. If no fuel squirts out, the pump is bad.
2. Engine runs rough or stalls under load. A weak pump may supply enough fuel at idle but not enough when you engage the mower deck or drive up a hill. The engine will sputter, hesitate, or stall when you push the throttle.
3. Hard starting after sitting. A fuel pump with a small leak can lose prime overnight. You will need to crank the engine for a long time before it starts, and sometimes you have to pour fuel into the carburetor to get it going.
4. Fuel leaks from the pump. The diaphragm can crack and allow gasoline to seep out of the vent port. You may see drips on the side of the engine or smell fuel strongly. This is a fire hazard and must be fixed immediately.
5. Oil smells like gasoline. If the diaphragm tears completely, fuel can be pumped directly into the engine crankcase through a passage. Your oil level will rise and the oil will smell like gas. This can cause serious engine wear.
6. No fuel in the carburetor bowl. You can look through the carburetor drain vent or remove the bowl to confirm. If it is dry despite the tank being full, the pump is not delivering fuel.
I have owned John Deere 318 tractors for many years and I have replaced fuel pumps on them multiple times. The symptoms are always the same. In every case, the tractor sat for a period of time and the rubber diaphragm dried out. Do not assume the carburetor is dirty first. Always test the fuel pump because it is a simple check.
Testing the John Deere 318 Fuel Pump
Before buying a new pump, you need to verify that the old one is actually bad. Testing takes five minutes and requires only a piece of hose and a container.
Step 1: Check for fuel flow at the carburetor
Disconnect the fuel line at the carburetor. Put the end of the hose into a clean can. Crank the engine for ten seconds. You should see a strong, pulsing stream of fuel. If you see a weak drip or nothing, the pump is suspect.
Step 2: Check for vacuum at the pump inlet
Disconnect the fuel line from the tank that goes to the pump inlet. Place a finger over the inlet port or use a vacuum gauge if you have one. Crank the engine. You should feel strong suction. If there is no suction, the pump is not working. If there is suction but no fuel comes out the outlet, the pump might be blocked internally.
Step 3: Check for pressure at the pump outlet
Reconnect the tank line. Disconnect the outlet line at the pump. You can use a fuel pressure gauge designed for small engines. With the engine cranking, you should see about 2 to 4 psi. Most mechanical pumps on these tractors push fuel rather than pull it, so pressure is important.
Step 4: Test the pushrod
Remove the pump from the engine (two bolts). Pull out the pushrod. It should be straight and at least 3 inches long. Measure it with a caliper or ruler. The factory specification is about 3.050 inches for the Onan engine. If it is shorter than 2.9 inches, it is worn. A worn pushrod will not move the pump enough to pump fuel.
Step 5: Check for leaks
Attach a short hose to the pump's vent port. Try to blow into it. If air passes through freely, the diaphragm is torn. You can also submerge the pump in water while plugging the inlet and outlet and applying air pressure. Any bubbles indicate a leak.
If you confirm the pump is bad, do not try to repair it. The diaphragm is not sold separately. Replace the whole pump. If the pushrod is worn, replace it too. They are available as a set for the John Deere 318.
Choosing the Right Replacement Fuel Pump
Not all fuel pumps are the same. You must get the exact pump designed for your engine. The John Deere 318 uses two basic pump types depending on the engine.
For Onan P218G engine (most common)
The correct pump is John Deere part number AM107134 for the earlier version or AM107135 for a later version. These are mechanical pulse pumps. They are identical in function but have slightly different inlet port angles. You can also use an aftermarket pump like the Stens 120-950 or Oregon 18-035. These are good quality and cost less than the OEM parts.
For Kawasaki FD590V engine
The pump part is John Deere AM118785 or Kawasaki 49065-0725. This pump is also mechanical but the pushrod is different. The mounting bolt pattern is the same as the Onan pump, but the outlet line is on the opposite side.
Important details
Always check the nipple size. The original pumps have 1/4 inch barbed nipples for rubber hose. Some aftermarket pumps use a metal outlet that is 5/16 inch. You may need to change your hose size. Buy a pump that matches your existing hose setup.
Avoid universal pumps designed for different brands. They may not have the correct pushrod depth. The wrong pump will not make enough pressure.
Gaskets and seals
The pump mounts to the engine block with a thin paper or rubber gasket. Most new pumps come with a gasket. If not, buy a tube of gasket sealer or a sheet of gasket material and cut your own. A dry mount will cause oil leaks.
Tools and Materials for the Replacement
You will need basic tools. Gather these before you start.
Tools:
- Socket set with 3/8 inch and 9/16 inch sockets
- Combination wrenches: 1/2 inch, 9/16 inch
- Screwdrivers: flathead and Phillips
- Pliers for hose clamps
- A small pick or awl to remove old gasket
- Mirror and flashlight to see the pushrod
Materials:
- New fuel pump with gasket
- New pushrod if worn
- New fuel line hose: 1/4 inch ID, about 2 feet
- New hose clamps, spring type or screw type
- Container to catch fuel spill
- Clean rags
- Carburetor cleaner spray
You may also need a new fuel filter. The John Deere 318 has a small inline filter near the tank or the pump. If it is clogged, the new pump will still fail to supply fuel. Replace it while you are at it.
Step-by-Step Installation Guide
This process works for both Onan and Kawasaki engines. Safety first: work in a well-ventilated area, disconnect the spark plug wire, and keep a fire extinguisher nearby because you will be handling gasoline.
Step 1: Drain the fuel tank or pinch the line
To avoid a huge spill, either drain the tank into a clean can or pinch the fuel line with a pair of vise grips taped to protect the hose. I prefer to use a shutoff valve installed on the tank outlet, but if you do not have one, just pinch the line.
Step 2: Remove the air cleaner assembly
Take off the cover and the air filter to give yourself more room. You do not need to remove the carburetor, but you should be able to see the fuel line connections.
Step 3: Disconnect the fuel lines at the pump
Identify the three hoses on the pump. The inlet is from the tank, the outlet goes to the carburetor, and the vent has a short piece of hose that may just have open end or a small filter. Use pliers to loosen the clamps and pull each hose off. Be ready for a small amount of fuel to drip.
Step 4: Remove the two mounting bolts
Use a 9/16 inch socket and a ratchet. The bolts are usually located at the top and bottom of the pump. On some engines, there is a third bolt hidden under hoses. If the bolts are rusted, spray penetrating oil and wait a few minutes.
Step 5: Pull the pump straight out
Gently wiggle the pump off the block. The pushrod may stay in the engine bore. If it does not fall out, use a magnet or a piece of stiff wire to extract it. Do not rotate the engine while the pump is off unless you close the pushrod bore with a finger. The pushrod can fall into the crankcase and cause damage.
Step 6: Inspect the pushrod and the bore
Look for wear on the pushrod tip. Compare it to the new rod. Also check the bore for scoring. If the bore is rough, you may need to use emery cloth to smooth it. A new pushrod is cheap, so always replace it if you are uncertain.
Step 7: Clean the mounting surface
Use a scraper or a razor blade to remove old gasket material. Be careful not to scratch the aluminum block. Wipe with a clean rag. Apply a thin film of grease to the new gasket to hold it in place.
Step 8: Install the new pushrod and pump
Insert the new pushrod into the engine block. Make sure it goes all the way in and that the chamfered end faces the pump. Place the new pump with gasket onto the two bolts. Tighten the bolts alternately to avoid tilting. The torque specification is about 15 foot-pounds, but if you do not have a torque wrench, tighten firmly by hand.
Step 9: Reconnect the fuel lines
Attach the inlet hose from the tank to the pump port marked with an arrow pointing in. Attach the outlet hose to the arrow pointing out. Attach the vent hose. Use new clamps and tighten them enough to prevent leaks.
Step 10: Install the fuel filter if you have one
Replace the filter with new one. Make sure the arrow points toward the pump or the carburetor, depending on which filter you are using. Many aftermarket filters have a directional arrow.
Step 11: Reconnect the spark plug wire and air cleaner
Double-check all hoses and clamps. Turn the fuel valve on if you have one.
Step 12: Prime the system
Crank the engine a few times without starting to let the fuel pump fill the line. Expect to crank for about 15 seconds on a dry system. Once you see fuel at the carburetor, start the engine. It may run rough for a few seconds while the carburetor bowl fills.
Common Mistakes to Avoid
New pump still does not work? Check these pitfalls.
1. Installed the wrong pump. If the pushrod does not match the pump arm, the pump will not actuate. Double-check part numbers.
2. Forgot to remove the old gasket. A double gasket can prevent the pump from seating correctly and cause an oil leak.
3. Pinched the fuel line. If the hose is kinked or blocked, the pump cannot pull fuel. Route hoses cleanly.
4. Clogged fuel filter. A filter that looks clean can still have internal blockage. Replace it yearly.
5. Air leak in the inlet. If the inlet hose is cracked or the clamp is loose, the pump will pull air instead of fuel. Check for bubbles in the line.
6. Worn pushrod. Even with a new pump, a worn pushrod will limit pump stroke. Always measure it.
7. Engine oil too high. If fuel leaked into the crankcase, you will see oil overfilled. Change the oil and filter. Running with gas diluted oil will damage bearings.
Maintenance Tips for the Fuel Pump
Once you have a working pump, you can extend its life.
1. Use ethanol-free gasoline whenever possible. Ethanol attracts moisture and degrades rubber diaphragms. If you must use ethanol gas, add a fuel stabilizer.
2. Run the carburetor dry before storing the tractor. Turn off the fuel valve and run the engine until it stalls. This prevents fuel from sitting in the pump and evaporating.
3. Replace the fuel lines every two years. Rubber hoses harden and crack internally. A broken hose can send debris into the new pump.
4. Check the pushrod when you change oil. Every 100 hours, pull the pump and look at the pushrod. If it shows wear, replace it.
5. Keep the engine cooling fins clean. Overheating can accelerate rubber wear on the pump diaphragm.
Final Thoughts
The John Deere 318 fuel pump is a simple part that you can replace in about an hour on your own. The cost is around $20 to $50 for a quality aftermarket pump, and the tools needed are common. The key is to diagnose the problem correctly by testing the pump and pushrod before you buy parts. With a new pump, your 318 will run smoothly and reliably for many more years. I recommend buying a spare pump and pushrod to keep on the shelf. They are inexpensive and when the pump fails, you will have it ready. Do not ignore the warning signs of a bad pump; fix it quickly to avoid engine damage and keep your tractor operational.
Remember to always work safely with gasoline and protect your tractor from fire hazards. If you have any questions about this repair, consult the John Deere 318 service manual or forums. Many experienced owners share their tips online. Happy troubleshooting and enjoy your John Deere.