MTD 790 series User Manual

Problem Cause Remedy
Engine fails to start PTO/Blade engaged. 1.
Spark plug wire disconnected.2.
Fuel tank empty, or stale fuel. 3.
Choke not activated.4.
Faulty spark plug.5.
Blocked fuel line.6.
Engine flooded.7.
Parking brake not engaged8.
Throttle control lever not in correct starting 9.
position.
Place knob (or lever) in disengaged (OFF) 1.
position.
Connect wire to spark plug. 2.
Fill tank with clean, fresh (less than 30 days 3.
old) gas.
Place the throttle control in CHOKE position.4.
Clean, adjust gap or replace plug. 5.
Clean fuel line and replace fuel filter. 6.
Crank engine with throttle in FAST position.7.
Engage parking brake. 8.
Place throttle lever to FAST position. 9.
Engine runs erratic Unit running with CHOKE activated. 1.
Spark plug wires loose. 2.
Blocked fuel line or stale fuel. 3.
Vent in gas cap plugged. 4.
Water or dirt in fuel system. 5.
Dirty air cleaner. 6.
Move the throttle contol out of the CHOKE 1.
position.
Connect and tighten spark plug wire. 2.
Clean fuel line; fill tank with clean, fresh 3.
gasoline and replace fuel filter, is so equipped.
Clear vent or replace cap if damaged. 4.
Drain fuel tank. Refill with clean, fresh 5.
gasoline.
Replace air cleaner paper element or clean 6.
foam precleaner, is so equipped.
Engine overheats Engine oil level low. 1.
Air flow restricted. 2.
Fill crankcase with proper amount and 1.
weight of oil.
Clean grass clippings and debris from around 2.
the engine’s cooling fins and blower housing.
Engine hesitates at high
RPM
Spark plug gap too close. 1. Remove spark plug and reset the gap. 1.
Engine Idles rough Spark plug fouled, faulty or gap too wide. 1.
Dirty air cleaner. 2.
Replace spark plug. Set plug gap. 1.
Replace air cleaner element and/or clean 2.
pre-cleaner, if so equipped.
Excessive vibration Cutting blade loose or unbalanced. 1.
Damaged or bent cutting blade. 2.
Tighten blade and spindle. Balance blade.1.
Replace blade. 2.
Mower will not mulch grass Engine speed too low. 1.
Wet grass. 2.
Excessively high grass. 3.
Dull blade. 4.
Place throttle in FAST (rabbit) position.1.
Do not mulch when grass is wet. 2.
Mow once at a high cutting height, then 3.
mow again at desired height or make a
narrower cutting swath.
Sharpen or replace blade. 4.
Uneven cut Deck not leveled properly. 1.
Dull blade. 2.
Uneven tire pressure. 3.
Perform side-to-side deck adjustment. 1.
Sharpen or replace blade. 2.
Check tire pressure in all four tires. 3.
Troubleshooting
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MTD 790 series Specifications

General

Engine Displacement	190 cc
Drive System	Rear-wheel drive
Deck Material	Steel
Starter Type	Recoil
Mulching Capability	Yes
Bagging Capability	Yes
Side Discharge Capability	Yes
Wheel Size	8 inches (rear)