Honda Foreman 520 Turns Over But Doesn't Start
⚡ Quick Answer
The Honda Foreman 520 may not be starting due to fuel delivery issues or ignition failure. Start with checking the fuel system and spark plug condition to identify the specific cause.
What do you want to do?
Most Likely Cause
Skipped Timing Chain
The camshaft timing chain may have jumped a tooth on the cam sprocket due to a failing chain tensioner. Use a 14mm socket to check the manual tensioner and verify the 'T' mark alignment on the flywheel.
Start here — this is the most common reason for this symptom.
Why This Problem Happens
When your Honda Foreman 520 cranks but fails to fire, and specifically pushes the air box lid up, you are witnessing a textbook case of significant intake backfire caused by incorrect valve timing or a failure of the automatic decompression system. The physical mechanism behind this involves the intake valve being open while the piston is undergoing the combustion or power stroke. Instead of the explosion being contained in the combustion chamber to drive the piston downward, the flame front rushes past the unseated or incorrectly timed intake valve into the intake tract and air box. This sudden, violent pressure spike creates a shockwave that travels backward through the throttle body, lifting the air box lid as it attempts to vent. This condition indicates that the engine is severely out of time or suffering from catastrophic valve train failure, preventing the necessary compression build-up required for a successful start. Often, this is a precursor to more severe engine damage, such as piston-to-valve contact, if the timing chain has skipped teeth on the camshaft sprocket.
Common Symptoms
- Air box lid physically lifts during cranking
- Audible thumping or popping sound from the intake
- Engine cranks at varying speeds without catching
- Noticeable loss of compression through the intake
- Excessive fuel vapor or blow-by coming from the throttle body
Before You Buy Parts
Quick, free inspections — check these first. Most repairs don't actually need replacement parts.
Complete Resource Guide
Complete Small Engines Troubleshooting Guide
Brand Resource Hub
The Ultimate Honda Small Engine Repair & Service Hub
Repair Overview
4–8 hours
$150–$400
First Checks — Start Here
- 1Check if there is fuel in the tank.
- 2Inspect the air filter for blockages.
- 3Examine the spark plug for damage or debris.
- 4Ensure proper battery voltage for ignition.
- 5Look for any loose or damaged electrical connections.
Safety Warnings
- !Ensure the spark plug is removed so the engine does not accidentally start during manual rotation.
- !Keep hands clear of the cooling fan and belt areas while the engine is pressurized.
- !Use a torque wrench to ensure the camshaft bearing cap bolts are tightened to exact Honda specifications upon reassembly.
- !Only perform this adjustment when the engine is completely cold to ensure thermal expansion does not affect settings.
- !Be careful when removing the tensioner as the internal spring can eject if not handled correctly.
- !Always disconnect the negative battery cable before performing electrical or sensor-related inspections.
- !Assuming the problem is electrical and replacing the spark plug or ignition coil unnecessarily
Always disconnect the spark plug, work in a well-ventilated area, and consult a professional if unsure.
Most Likely Causes
Ranked by likelihood — tap each to see diagnosis details.
The camshaft timing chain may have jumped a tooth on the cam sprocket due to a failing chain tensioner. Use a 14mm socket to check the manual tensioner and verify the 'T' mark alignment on the flywheel.
Carbon buildup or a bent valve stem can cause the intake valve to remain partially open. Perform a leak-down test at top-dead-center to identify air escaping through the intake port.
🔧 Step-by-Step Fix Guide
Verify Mechanical Timing
Remove the timing inspection cover on the flywheel and the valve cover. Rotate the crankshaft to the TDC mark and verify the alignment marks on the camshaft sprocket are parallel with the cylinder head surface.
Ensure the spark plug is removed so the engine does not accidentally start during manual rotation.
Perform a Cylinder Leak-Down Test
Apply 90 PSI of air to the spark plug hole while at TDC. Listen for air rushing through the air intake box; if audible, you have confirmed an intake valve sealing issue.
Keep hands clear of the cooling fan and belt areas while the engine is pressurized.
Inspect Camshaft Decompressor
Remove the camshaft assembly and inspect the decompression pin for debris or spring failure. The pin should move freely and return under spring tension.
Use a torque wrench to ensure the camshaft bearing cap bolts are tightened to exact Honda specifications upon reassembly.
Check Valve Clearances
Use a precision feeler gauge to verify intake and exhaust clearances. If the intake valves are at zero clearance, the valve is being held open during the compression stroke.
Only perform this adjustment when the engine is completely cold to ensure thermal expansion does not affect settings.
Inspect Timing Chain Tensioner
Remove the tensioner assembly to see if it is fully extended. If the plunger is at its maximum limit, the timing chain is stretched beyond service limits and must be replaced.
Be careful when removing the tensioner as the internal spring can eject if not handled correctly.
Examine Throttle Body for Obstructions
Inspect the butterfly valve and intake boot for physical damage or debris that might be causing a reversion. A torn intake boot can create an air leak that confuses the fuel injection map.
Always disconnect the negative battery cable before performing electrical or sensor-related inspections.
What To Test Next
If fuel delivery checks out, the next thing to inspect is spark — remove the spark plug, ground its threads to the engine block, and crank the engine to look for a visible blue spark.
Component Reference
Carburetor & Fuel Intake
The carburetor mixes air and fuel for combustion. A clogged jet or stuck float is the #1 cause of small engine starting and surging problems.
Spark Plug & Ignition System
The spark plug ignites the air-fuel mixture. A fouled plug, wrong gap, or failing ignition coil will prevent the engine from firing.
Air Filter & Intake
A clogged air filter starves the engine of air, causing rich running, power loss, and hard starting. Inspect and clean or replace it each season.
Fuel System
Stale fuel is the most common cause of seasonal starting failures. Fuel breaks down in 30 days, leaving varnish that clogs carburetor jets and fuel filters.
Photos for educational reference. Actual parts may vary by make and model.
Common Mistakes to Avoid
Assuming the problem is electrical and replacing the spark plug or ignition coil unnecessarily
Adjusting valves while the engine is still warm, leading to incorrect specs
Ignoring the timing chain tensioner health when timing appears only slightly off
Attempting to force-start the engine repeatedly, which can damage the piston crown
If This Didn't Fix It
Still having trouble? These are the next things to check:
Get the Exact Parts for Your Machine
Tell us your equipment's year, make, and model — we'll search for parts that actually fit, not generic ones.
Finding parts for
honda foreman 520 turns over but
Required Gear
Matched to your honda foreman 520 turns over but — click to find the exact fit on Amazon.
Timing Chain Kit
If the chain has stretched or skipped teeth causing the valve timing issue, a new chain is required to restore proper engine synchronization.
Intake Valve
Since the air box lid is being pushed up, it indicates a backfire through the intake, which often suggests the intake valve is bent or stuck in the open position.
Valve Cover Gasket
Accessing and checking the valve clearances and timing chain requires removing the valve cover, which necessitates a fresh gasket to prevent oil leaks upon reassembly.
Camshaft Decompression Assembly
The failure of the internal decompression mechanism is a known issue on these engines that can cause timing erraticity and starting failure, requiring full replacement of the unit.
Cylinder Head Gasket
If the leak-down test confirms a damaged intake valve or piston crown resulting from timing failure, the head must be removed, requiring a new gasket for a proper seal.
Affiliate Disclosure: Lil Engine may earn commissions from qualifying purchases.
Pro Tips from the Community
Real-world fixes from Reddit, YouTube & forums.
"Check for a broken timing chain or belt; if the flywheel is spinning while pushing the air box up, that could indicate a serious internal issue."
YouTube comments"Inspect the valves for clearance; a sticking valve can cause compression issues and prevent starting."
TractorByNet Forum"Remove and clean the spark plug; if it’s flooded, it can prevent the engine from igniting properly, and fuel might be pushing back through the air intake."
Reddit r/lawncare"Check the fuel lines for blockage; an obstruction can stop fuel from reaching the engine, leading to a no-start scenario."
DoItYourself.com"Make sure the kill switch isn’t stuck; a non-responsive switch can prevent the engine from firing up entirely."
LawnSite.com ForumPrevent This From Coming Back
Strict adherence to oil change intervals using JASO-MA certified oil to prevent timing chain wear
Regularly cleaning the air filter to prevent fine dust from causing valve stem carbon buildup
Periodically verifying valve clearances every 1,000 miles to catch drift before it becomes a failure
Monitoring for the 'timing chain rattle' sound during idle and addressing it immediately
Prevent This From Happening Again
While you're fixing it, stock up on the maintenance essentials that keep your small engines running right.
Spark Plug
The cheapest, fastest fix for most small engine starting problems.
Get on AmazonCarburetor Cleaner
Cleaning the carb is the #1 fix for surging and stalling engines.
Get on AmazonFuel Stabilizer
Prevents the stale fuel problems that cause most seasonal no-starts.
Get on AmazonAffiliate Disclosure: Lil Engine may earn commissions from qualifying purchases.
Frequently Asked Questions
No, bad fuel causes poor performance but will not generate enough pressure to lift the air box lid. This symptom is strictly mechanical in nature.
Video Help
Helpful videos showing these repairs in action.
Share Your Repair
Real-world fixes help everyone. Share what worked and your repair becomes part of Lil Engine's community database.
Related Problems
More Small Engines GuidesRelated Maintenance Articles
Related Symptoms
Carburetor / Fuel Issues
Related Searches
Honda small engine Guides
Did this help?
Your feedback helps improve guides for everyone.