Good write-up — you already did a lot of the right things. A 2005 Polaris Ranger 500 is pretty simple fuel-wise, so the good news is there aren’t many mysterious sensors that “shut fuel off”. This problem is almost always mechanical: fuel delivery, vacuum, carb, or spark.
Let’s answer your two questions directly, then I’ll give you a short attack plan.
1) Is there a sensor that restricts fuel flow?
No.
On a 2005 Ranger 500:
There is no electronic fuel control, no ECU, and no sensor that shuts fuel off.
Fuel flow is controlled by only:
• Fuel pump (vacuum-operated)
• Fuel lines
• Carb float & needle
• Tank venting
• Petcock / fuel valve (if equipped)
If the float bowl was full, the pump was doing its job. The engine dies because fuel is not getting from the bowl into the engine through the jets, not because something "turned the fuel off."
2) Why won’t it run now when it ran for 30 seconds?
This is classic carb-clog behavior.
It ran on:
• Cleaner fluid
• Fuel already in the bowl
• Whatever fuel partially flowed before debris moved
Then it died because:
Most likely causes (ranked in probability):
A) Pilot jet or main jet is plugged (MOST COMMON)
When varnish breaks loose, it moves downstream and immediately blocks tiny jet openings.
Symptoms:
• Runs briefly then dies
• Won’t restart
• Bowl has fuel but engine acts starved
• Starter fluid allows momentary run
✅ Fix:
Pull carb again and:
• Remove pilot jet
• Remove main jet
• Remove emulsion tube
• Spray carb cleaner through everything
• Blow with compressed air (not optional)
• Pass thin wire through jets if needed
Tank vent is clogged → vacuum in tank
If the tank cannot breathe, fuel flow stops after a short run.
✅ Test:
Remove gas cap and try to start it.
If it runs, vent is plugged.
C) Vacuum line leaking to fuel pump
If the vacuum line is cracked, loose, or plugged, the fuel pump will stop after initial fuel.
✅ Test:
Pull vacuum line off pump and crank engine.
You should feel strong pulsing suction.
No vacuum = hose issue or intake leak.
D) Amazon carb quality issue
Low-price carbs often have:
• Wrong float height
• Faulty needle
• Leaky bowl
• Wrong jet size
• Improper gaskets
Fuel leaking out the bottom = float/needle defective.
✅ Use the OEM carb you rebuilt after cleaning it again.
E) Spark failure after warm-up
Much less common, but possible with an aging ignition coil or stator.
✅ Test:
Pull spark plug and check immediately after it dies.
Spark should be bright blue.
A very likely scenario in your case:
It ran well → debris moved → jet plugged → bowl stayed full → engine starved → now dead.
What I recommend you do next (simple order):
Step 1:
Remove gas cap and try to start it (rule out tank vent)
Step 2:
Pull your ORIGINAL carb back off and:
• Remove pilot + main jets
• Spray + air blast them thoroughly
• Make sure spray shoots cleanly out of idle port
• Reassemble
Step 3:
Check vacuum line to fuel pump:
Crank with line removed → must feel suction.
Step 4:
Ignore the Amazon carb for now.
Use your rebuilt OEM carb only.
Step 5:
Verify spark after it dies.
I