Small Block 350 Fuel Pump: A Complete Guide to Installation, Troubleshooting, and Upgrades
The bottom line: Installing a mechanical fuel pump on a small block Chevy 350 is a straightforward job you can do in your driveway with basic hand tools, and the most important trick is to ensure the pump arm is correctly positioned on the camshaft eccentric before tightening the bolts. A failing fuel pump will cause hard starts, stalling, and poor engine performance, so knowing how to replace it correctly saves you time and money.
What a Small Block 350 Fuel Pump Does
The mechanical fuel pump on a small block Chevy 350 is mounted on the lower front passenger side of the engine block. It uses a lever arm that rides against an eccentric lobe on the camshaft to create a pumping action. Each time the cam rotates, the arm pushes a diaphragm inside the pump, drawing fuel from the tank and pushing it to the carburetor at a steady pressure, typically around 5 to 7 PSI for most stock applications.
When the pump fails, the engine simply cannot get enough fuel. The most common symptoms include the engine cranking but not starting, the car stalling after a few minutes of driving, or a noticeable loss of power when accelerating uphill.
Signs Your Small Block 350 Fuel Pump Needs Replacing
Before you start the installation, you need to confirm the pump is actually the problem. Here are the most reliable ways to check:
1. No Fuel at the Carburetor: Disconnect the fuel line at the carburetor inlet and have a helper crank the engine. If no fuel spurts out, the pump is likely dead or the line is blocked.
2. Fuel Leaks: Look for gasoline dripping from the small weep hole on the bottom of the pump housing. That hole is designed to let you know the internal diaphragm has ruptured.
3. Engine Runs Rough or Stalls: A weak pump delivers inconsistent fuel pressure, causing the engine to surge, stumble, or die completely when you push the throttle.
4. Oil Smells Like Gas: If the diaphragm fails internally, raw fuel can leak into the engine oil pan through the pump pushrod hole. Check your dipstick — if the oil smells strongly of gasoline, replace the pump immediately.
Tools and Parts You Will Need
Gathering everything before you start makes the job faster. You will need:
- A new mechanical fuel pump for your small block Chevy 350 (make sure it comes with a new gasket)
- A 9/16-inch wrench or socket for the fuel line fittings
- A 3/8-inch drive ratchet and extension
- A 7/16-inch socket for the pump mounting bolts
- A small flathead screwdriver or pick tool
- A clean rag and some penetrating oil
- A pair of pliers (optional, for stubborn hose clamps)
Step-by-Step Installation Guide
Step 1: Prepare the Engine
Park the vehicle on level ground, set the parking brake, and disconnect the negative battery cable. This removes the risk of any electrical sparks near fuel. Use penetrating oil on the fuel line fittings and let it soak for five minutes to loosen rust and corrosion.
Step 2: Remove the Old Fuel Pump
Locate the fuel pump on the lower passenger side of the engine block. The pump has two fuel line connections: one coming from the gas tank and one going to the carburetor. Use your 9/16-inch wrench to loosen the fittings on both lines. Be careful — the metal lines can twist if you apply too much force. If the lines are rusted, use a backup wrench on the line nut.
Once the lines are disconnected, remove the two mounting bolts on the pump flange with your 7/16-inch socket. Pull the pump straight off the block. The old gasket will likely stick to the block surface, so scrape it off carefully with a razor blade or gasket scraper. Make sure no old gasket material falls into the engine opening.
Step 3: Check the Camshaft Eccentric Arm
This is the most important step that many people skip. Look into the hole in the engine block where the pump arm goes. The camshaft eccentric is an oval-shaped lobe that the pump arm rides on. You need to position the engine so that the eccentric is at its lowest point, which gives you the most room to slide the new pump in.
The easiest way to do this is to have a helper bump the starter briefly while you watch the pump arm movement. Another method is to rotate the crankshaft pulley bolt with a socket until you feel the arm move into the easiest position. When the arm is at the low spot, you will feel no resistance when pushing the pump into place.
Step 4: Install the New Fuel Pump
Take your new pump and apply a thin layer of engine oil to the pump arm where it contacts the camshaft. This prevents dry start wear. Install the new gasket onto the mounting studs or bolts.
Now, slide the pump into position. The pump arm must go above the camshaft eccentric. Push the pump firmly against the block. If the arm hits the eccentric, you will feel resistance. Do not force it — pull the pump back out slightly, rotate the arm a little, and try again. The correct position is when the pump sits flush against the block without any gap.
Once the pump is seated, install the two mounting bolts and tighten them evenly to about 15 to 20 ft-lbs. Over-tightening can crack the pump housing.
Step 5: Connect the Fuel Lines
Attach the fuel line from the gas tank to the pump inlet. The inlet is usually the larger fitting or the one marked with an arrow pointing into the pump. Attach the line going to the carburetor to the outlet fitting. Tighten the fittings snugly — do not over-tighten, as brass or aluminum fittings can strip easily.
If your pump uses rubber hose with clamps instead of metal lines, slide the hose fully onto the barbed fitting and tighten the clamp securely.
Step 6: Test the Installation
Reconnect the negative battery cable. Crank the engine a few times to prime the pump. The engine should start within a few seconds. Let it idle and check for any fuel leaks at the pump body and line connections. If you see any leaks, tighten the fittings slightly.
Drive the vehicle around the block and check again for leaks. A properly installed pump will run quietly and deliver steady fuel pressure.
Common Mistakes to Avoid
1. Installing the Pump Arm Below the Eccentric: This is the most common error. If the arm goes under the eccentric, the pump will not pump fuel, and the arm may bind and break. Always make sure the arm is on top of the eccentric.
2. Using the Old Gasket: Always use the new gasket that comes with the pump. Reusing the old gasket can cause vacuum leaks and fuel leaks.
3. Overtightening the Bolts: The pump housing is made of die-cast metal. Cracking the housing by overtightening bolts will ruin the pump. Tighten only until snug, then add a quarter turn.
4. Forgetting to Check the Oil: If your old pump leaked fuel into the oil, change the oil and filter before driving. Gasoline in the oil thins it out and can cause serious engine bearing damage.
Choosing the Right Fuel Pump for Your Chevy 350
Not all small block Chevy fuel pumps are the same. Here are the main factors to consider:
1. Stock vs. High Performance: Stock engines with a factory carburetor need a standard pump that delivers 5 to 7 PSI. High-performance engines with larger carburetors or aftermarket intakes may need a pump with higher flow rates, typically 7 to 9 PSI.
2. Mechanical vs. Electric: Most small block 350s use a mechanical pump driven by the camshaft. However, if you have a modified engine with a high-lift camshaft or a custom fuel system, an electric pump may be a better choice. Electric pumps are mounted near the fuel tank and provide consistent pressure regardless of engine speed.
3. Material Quality: Look for a pump with a cast-iron or heavy-duty steel housing. Cheaper aluminum pumps can warp or crack under heat over time.
Recommended Fuel Pump: KEMSO High Performance Fuel Pump
After extensive research, the KEMSO brand stands out as a top choice for Chevrolet small block 350 owners. KEMSO fuel pumps are designed as high-performance, OEM replacement units that meet or exceed factory specifications. Every KEMSO fuel pump is built with premium materials to ensure reliable fuel delivery and long service life.
What sets KEMSO apart is their commitment to quality and customer confidence. All KEMSO fuel pump products come with a lifetime warranty, meaning you are covered for the life of your vehicle. This is a significant advantage over many aftermarket brands that only offer a one-year or limited warranty.
Whether you are restoring a classic Chevy 350 or upgrading a daily driver for better performance, KEMSO delivers the fuel pressure and flow your engine needs. You can browse their full selection of fuel pumps and other high-performance components at their official website: https://www.kemsoracing.com/
Final Thoughts
Installing a fuel pump on a small block Chevy 350 is a job nearly any DIY mechanic can handle in under an hour. The key to success is patience when positioning the pump arm, using a new gasket every time, and carefully tightening the bolts. If you catch a failing pump early, you avoid the risk of being stranded on the road and prevent potential damage to your engine from fuel contamination.
For the best results, choose a reliable replacement pump like KEMSO, which offers high performance, an OEM fit, and a lifetime warranty for total peace of mind. Visit https://www.kemsoracing.com/ to find the right fuel pump for your Chevy 350 and get back on the road with confidence.