Case 350 Crawler with Roosa Master Pump Refuses to Start

[MikePhua]

Quick answer
A 1973 Case 350 crawler with a 188 diesel engine may fail to start due to air intrusion, fuel starvation, or internal sticking in the Roosa Master injection pump. Even with fuel at the injectors, the metering valve, transfer pump regulator, and return line integrity must be verified to restore proper injection pressure and timing.
Case 350 crawler background and fuel system design
The Case 350 crawler was introduced in the early 1970s as a compact dozer and loader platform for utility and light construction work. Powered by a 188 cubic inch four-cylinder diesel engine, it featured:

• A gravity-fed fuel system
  
• Dual fuel filters
  
• A Roosa Master DB-series injection pump
  
• Mechanical injectors with return lines
  

The Roosa Master pump includes a metering valve (MV), transfer pump, and internal fuel cavity. It relies on clean, bubble-free fuel and precise internal pressure regulation to deliver timed injection pulses to each cylinder.
Failure symptoms and initial observations
After years of reliable operation, the machine failed to restart following a cold-weather shutdown. The return line at injector #1 had loosened, causing fuel spray and engine stall. Despite replacing filters, bleeding lines, and confirming fuel at injectors, the engine refused to fire.
Key symptoms:

• Fuel dribbles at injector lines but no ignition
  
• Engine cranks fast with good compression
  
• Fuel cavity inside pump not full during inspection
  
• Bubbles observed during cranking
  
• Metering valve rotates freely
  
• Transfer pump regulator contains steel plug and spring
  

These signs suggest partial fuel delivery but insufficient pressure or timing to trigger injection.
Roosa Master pump diagnostics and internal checks
The Roosa Master DB-series pump requires:

• 2600 PSI injection pressure to open nozzles
  
• Free movement of the metering valve to modulate fuel quantity
  
• Proper operation of the transfer pump regulator to maintain internal pressure
  
• Clear return lines to prevent backpressure
  

Recommendations:

• Loosen injector lines at the injectors and crank until clear fuel spurts without bubbles
  
• Inspect the transfer pump regulator for debris or damaged seals
  
• Confirm the stop lever is fully in the run position
  
• Check the fuel bowl and shutoff valve under the tank for blockages
  
• Ensure the fuel tank is at least 90% full to support gravity feed
  

One technician noted that a dry pump cavity and persistent bubbles indicate air intrusion or suction restriction. Even if air blows through the lines, debris may still block fuel flow.
Force priming and bleeding strategy
To force prime the system:

• Pressurize the fuel tank gently with compressed air (5–10 PSI max)
  
• Disconnect the inlet line at the pump and observe fuel flow
  
• Manually fill the pump cavity through the return fitting
  
• Crank with injector lines loose until fuel flows cleanly
  
• Avoid excessive starting fluid—use only minimal amounts during cranking
  

If the pump cavity remains dry or bubbles persist, consider removing the top cover and inspecting the metering valve shaft and internal seals.
Common pitfalls and overlooked issues

• Vacuum leaks: Cracked rubber lines or hardened grommets can suck air without visible leaks
  
• Fuel filter seal errors: Double gaskets or twisted seals can block flow
  
• Transfer pump piston binding: Internal corrosion may prevent pressure buildup
  
• Incorrect regulator adjustment: Tampering with the spring preload can disrupt fuel delivery
  

One rebuilder warned that adjusting the transfer pump regulator without proper tools can cause catastrophic overpressure or failure.
Conclusion
A Case 350 crawler that cranks but won’t start despite fuel at injectors likely suffers from internal pump issues, air intrusion, or fuel starvation. The Roosa Master DB-series pump must be fully primed, bubble-free, and internally functional to deliver injection pressure. With careful bleeding, cavity inspection, and regulator checks, the engine can be revived without replacing major components.