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78/83/90 Series Horizontal Shaft Engines
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Troubleshooting the EVAP System
There are four failure modes for the EVAP system:
• A leak in the system - will allow dirt ingestion.
• A blockage in the system (between the canister and the fuel tank) - acts a plugged vent.
• A blockage in the system (between the canister and the control panel) - The canister can not purge its
vapors.
• Charcoal canister poisoned (raw fuel in the canister) - prevents the canister from absorbing fuel vapors.
NOTE: The only failure mode that will affect the operation of the engine in a way the operator will notice is a
blockage in the system.
To test the system for a blockage:
1. Remove the fuel cap.
2. Clamp off the hose that runs from the canister to the
control panel.
See Figure 4.12.
3. Attach a vacuum pump to the vent port of the char-
coal canister. See Figure 4.12.
4. Apply a vacuum to the canister.
NOTE: When applying the vacuum, squeeze the
pump slowly. Too much vacuum can close
the roll over valve giving a false reading.
5. If the canister does not hold a vacuum, the canister
and the roll over valve are working properly.
NOTE: If the canister does hold a vacuum, test the
roll over valve to determine if the roll over
valve or the canister is at fault.
Figure 4.12
Figure 4.13
Charcoal canister
For Parts Call 606-678-9623 or 606-561-4983
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