Power Loss Issues on the Bobcat 773 Skid Steer

[MikePhua]

Background on the Bobcat 773
The Bobcat 773 is a popular compact skid-steer loader manufactured by Bobcat Company, known for its robust build and commonly-used in landscaping, construction, and material handling. With a hydrostatic drive and approximately 16.7 gpm (63 L/min) hydraulic flow and system pressure around 3,000 psi, it delivers good balance between power and compactness.  Over its production years, the 773 has earned a reputation for reliability — but also has some recurring power-related issues according to user reports.

Symptoms of the Power Problem

• The engine bogs down significantly when digging into a pile (“scoop into a pile”) and will almost stall when turning in place, even with an empty bucket.
  
• The prime‑bulb in the fuel supply line remains firm (not flat), but fuel doesn’t visibly return from the injection-pump return line, even under high idle.
  
• Soot buildup is found around the muffler and air-box area, suggesting possible combustion or airflow issues.
  
• In some cases, poor performance persists even after replacing fuel lift pump, fuel filter, and air filters.
  

Potential Causes and Expert Analysis
Based on mechanic insights and community knowledge, several possible underlying causes emerge:

1. Fuel Supply / Bleeder Valve Problems
   • The bleeder valve on the injection pump return line has a spring-and-ball check. If it's faulty, it can fail to maintain adequate pressure inside the injection pump, especially after bleeding.
     
   • A weak diaphragm-type lift pump may struggle to sustain the required pressure, particularly under load, leading to starvation when the bleeder valve is not retaining pressure.
     
   • Some experienced users suggest replacing the bleeder valve because when it fails, the pump can't maintain pressure, leading to power loss under heavy demand.
     
2. Fuel Pickup Tube Damage
   • A common failure point is the fuel pickup tube inside the fuel tank. If the tube cracks or breaks off near its top, it may draw air instead of fuel under load — a situation that mimics fuel starvation.
     
   • Because many 773s are older, the original pickup and its check-valve can deteriorate or rot, so inspecting and replacing this tube may restore reliable fuel flow.
     
3. Weak or Worn Injection Pump / Injectors
   • If basic fuel system components check out, the problem may lie in the injection pump itself (or injectors). Over time, internal wear (pistons, delivery valves) can reduce performance under high load.
     
   • Some mechanics recommend having an injection shop bench‑test or rebuild the pump if all external diagnostics fail.
     
4. Hydrostatic / Mechanical Load Issues
   • Heavy mechanical or hydraulic load (e.g., digging, turning) may exceed the machine’s ability to maintain engine speed if fuel delivery or timing is compromised.
     
   • Although not always explicitly stated by the original poster, other users note that weak drive motors, drive chain, or hydrostatic system issues can also feel like low engine power.
     
5. Chaincase / Final Drive Maintenance
   • Low oil, water contamination, or degraded lubrication in the chain case (final drive) can increase mechanical load and drag, reducing overall machine performance.
     
   • A service manager recommended draining and checking the chain‑case oil for signs of contamination and topping it off properly.
     

Troubleshooting Steps & Recommended Fixes
Here’s a structured approach based on community advice and expert experience:

• Verify Bleeder Valve Function
  Open the bleeder on the injection pump return, pump the primer bulb about 10‑12 times, then close the valve. Confirm it holds pressure and restricts backflow.
  
• Inspect and Replace Fuel Pickup Tube
  Remove the fuel tank (or access internally) to check the condition of the pickup tube. Replace it if it's broken, cracked, or its check valve is faulty.
  
• Check for Air in the Fuel System
  Disconnect the return line, submerge it in fuel, run the lift pump, and observe for bubble-free flow under low and high idle.
  
• Test or Rebuild Injection Pump
  If the bleeder valve and fuel lines are good, have the pump tested for internal wear. A rebuild or replacement may be necessary if performance issues persist.
  
• Inspect Chaincase Oil
  With the machine on a slope, remove the chaincase fill or level plug, check oil condition, and refill or replace if contaminated.
  
• Evaluate Engine and Air Systems
  Given soot around the muffler / air box, inspect for clogged air filters, excessive back pressure, or inefficient combustion. Replace or clean as needed.
  

Real-World Example
One 773 owner cleaned out the chaincase oil and discovered metal shavings, which indicated internal wear and added drag. After replacing the oil and ensuring proper levels, they saw a noticeable improvement in responsiveness and power under load.  Another user replaced the bleeder valve on their injection pump — restoring fuel pressure behavior and eliminating the engine bogging during hard turns.

Preventive Maintenance Tips

• Change the fuel filter on schedule — for many 773s, this is every 500 hours or per manufacturer recommendation.
  
• Inspect the chaincase oil regularly, especially on older machines, for contamination or low levels.
  
• Bleed the fuel system properly after filter changes or fuel line work.
  
• Monitor primer bulb condition; if it becomes too soft or damaged, it may not maintain the needed pressure to the pump.
  
• Keep the air intake clean and free of soot deposits or restricted airflow.
  

Conclusion
The power problems on a Bobcat 773 described here are most likely related to fuel delivery or pressure maintenance, rather than a simple mechanical or engine fault. Key suspects include a faulty bleeder valve on the injection pump, a deteriorated fuel-pickup tube, or internal wear in the injection pump. Mechanical drag from a poorly maintained chaincase can also contribute. Systematic diagnosis — starting from the fuel tank, through the pick-up, up to the injection pump, and finally checking the final drive — is critical. With careful troubleshooting and targeted repairs, these power issues can often be resolved without a full engine or major hydraulic rebuild.