Ryobi 790R trimmer Parts

Yes, you can use .095-inch trimmer line on a Ryobi 790R gas line trimmer if the cutting head is rated for that diameter; if the head is designed for thinner line, .095 can feed poorly, overload the engine, and increase vibration.

• Check the cutting head label or spool markings for the supported line diameter range.
• If the head is bump-feed, confirm the eyelets are large enough for .095 line.
• Make sure the line can unwind smoothly without binding.
• If the engine bogs down at full throttle, step down to a thinner line.
• If you are replacing worn head components, match the original style before changing line size.

Thicker line cuts heavier weeds better, but it also increases load on the clutch, drive shaft, and gearbox. If your 790R is tuned for lighter trimming, .095 can reduce RPM and make starting and acceleration feel weaker.

• Rewind the spool with even tension and avoid crossing wraps.
• Cut the ends cleanly and keep both tails equal length.
• Inspect the eyelets and spool case for grooves or melting.
• Verify the guard and string cut-off blade are intact and not chewing the line.

If you need to restore proper trimming performance, replacing worn head parts often helps more than upsizing line; see the spool case and eyelet 791-683301 and the string cut-off blade 791-682061.

Using the largest line the head supports gives better cutting without forcing the engine and driveline to work harder than necessary, which helps the trimmer run smoother and extends component life.

Last updated: February 2026

On the Ryobi 790R gas line trimmer, the priming bulb (purge bulb) is typically replaced by removing the air filter cover, disconnecting the fuel lines from the primer base, and installing the new bulb assembly in the same orientation so fuel flows correctly.

• Let the engine cool completely and work in a well-ventilated area.
• Empty the fuel tank or clamp the fuel lines to reduce spills.
• Take a quick photo of the fuel line routing before you pull anything off.
• Have needle-nose pliers, a small screwdriver, and shop towels ready.
• Replace cracked fuel lines at the same time; air leaks make priming fail.

1. Remove the air filter cover and air filter to access the carburetor/primer area.
2. Identify the two primer connections:
   • Fuel supply to primer (from carburetor).
   • Return line from primer (back to tank).
3. Mark the lines (tape or marker), then pull them off the primer nipples.
4. Remove the screws/clips holding the primer bulb base to the carburetor or housing.
5. Install the new primer bulb/base, tightening screws evenly (snug, not stripped).
6. Reconnect fuel lines to the correct ports, then reinstall the air filter and cover.
7. Prime until the bulb fills and you see fuel moving through the lines; then start the trimmer.

Correct routing is the difference between “starts” and “won’t prime.” Use this as a sanity check:

• Fuel line 791-181168 (cracked or loose lines cause hard starting and no-prime symptoms)
• Spark plug (fouled plug mimics fuel problems)
• Air filter (restricted airflow makes starting difficult)

A primer bulb does not “push fuel into the engine” as much as it purges air and pulls fuel through the carburetor circuit. If the bulb is cracked, stiff, or the lines leak, the Ryobi 790R will be hard to start, stall, or refuse to prime.

Last updated: February 2026

For a Ryobi 790R gas line trimmer, mix fresh unleaded gasoline with 2-cycle oil at a 40:1 ratio (3.2 oz of oil per 1 gallon of gas). Use oil labeled for air-cooled 2-stroke engines, then shake the fuel can well before filling.

• Start with an approved fuel container (not the trimmer tank).
• Add about half the gasoline first.
• Measure and pour in the 2-cycle oil.
• Add the remaining gasoline.
• Cap and shake for 10 to 15 seconds.
• Fill the trimmer; wipe up any spills before starting.

Use a quality 2-cycle oil intended for air-cooled outdoor power equipment. Avoid oils intended for water-cooled engines (such as many outboard motor oils) because they are formulated differently and can increase smoke, carbon buildup, and plug fouling in a trimmer.

The correct fuel mix protects the piston, cylinder, and crank bearings. Too little oil can cause rapid engine damage; too much oil can foul the spark plug, clog the muffler spark arrestor, and make the trimmer run poorly.

Fuel issues often show up as hard starting, surging, or stalling. Check these common items:

• Old fuel (drain and replace with a fresh 40:1 mix)
• Cracked or soft fuel lines (replace the fuel line 791-181086)
• Dirty carburetor passages (a rebuild may be needed)
• Restricted muffler/spark arrestor screen

Last updated: February 2026

To replace trimmer line on a Ryobi 790R gas line trimmer, we remove the spool, wind the correct diameter line in the proper direction, then feed the ends through the eyelets and reinstall the spool so it advances smoothly during use.

• Shut the engine off and let the muffler and gearbox cool completely.
• Disconnect the spark plug wire to prevent accidental starting.
• Clean grass and debris from the cutting head so the spool seats correctly.
• Use the line diameter recommended for your cutting head; most bump-feed heads use line in the 0.080 to 0.095 inch range.

1. Remove the spool: Press the two tabs on the spool cap (or unscrew the cap, depending on the head) and lift the spool out.
2. Remove old line: Pull out any remaining line and clear tangles.
3. Cut new line: Cut two equal lengths (commonly 10 to 15 feet each) unless your spool is designed for a single longer length.
4. Wind the line: Hook the line into the spool’s anchor slot and wind tightly in the direction of the arrow on the spool.
5. Feed through eyelets: Push each line end through the eyelets in the spool housing.
6. Reinstall and test: Seat the spool, reinstall the cap, then pull both ends evenly so the line moves freely.

• Line wound the wrong direction
• Line wound too loose or crossed over itself
• Wrong line diameter (too thick binds, too thin slips)
• Worn cutting head components; replace the head if needed using bolens line trimmer cutting head 791-147498

Correctly loaded trimmer line reduces jams, improves cutting performance, and prevents premature wear on the cutting head, drive shaft, and gearbox.

Last updated: February 2026

For the Ryobi 790R gas line trimmer, .095 trimmer line is the better all-around choice for most yards because it lasts longer and cuts thicker weeds with fewer breaks. .080 line is best for lighter grass trimming and edging when you want more control and easier feeding.

• Pick .095 if you regularly hit fence lines, curbs, thick weeds, or you want fewer reloads.
• Pick .080 if you mainly edge sidewalks and trim light grass, and you prefer a smoother feel.
• If the head struggles to feed thicker line, step down to .080 for more consistent feeding.
• If you are breaking line constantly, step up to .095 and slow your sweep speed slightly.
• Keep the line length correct; overlong line increases drag and breakage.

If line breaks too fast or the cut looks uneven, these wear items often make a difference:

• Bolens line trimmer string cut-off blade 791-682061 (trims line to the correct length)
• Bolens line trimmer cutting head 791-147498 (holds and feeds the line)
• Craftsman line trimmer spool case and eyelet 791-683301 (eyelet wear can increase friction and snapping)

Line diameter changes engine load, cutting speed, and how often the line snaps. Thicker line (.095) reduces downtime in tough growth; thinner line (.080) improves control for detail work and can feed more smoothly.

Last updated: February 2026

On the Ryobi 790R gas line trimmer, line breaks repeatedly when the cutting line is the wrong diameter, is fed too long, is installed incorrectly in the head, or is being cut by a damaged eyelet or cutter. Fixing the feed setup and removing sharp contact points stops most breakage.

• Use the correct line diameter for your cutting head (too thin snaps; too thick binds and breaks).
• Keep the line length reasonable; don’t run extra-long tails.
• Rewind the spool tightly and evenly; loose wraps snag and shear.
• Clean grass and grit out of the spool housing; debris overheats and frays line.
• Inspect the string cut-off blade for nicks or a bent edge.
• Check the head eyelets for grooves or sharp edges.

A trimmer line that breaks constantly usually means the line is being pinched, overheated, or cut by a sharp surface. Correct line size and a smooth line path protect the cutting head, reduce vibration, and improve fuel efficiency.

If the engine surges or stalls, the head can “grab” and shock-load the line. Check for cracked or loose fuel tubing and replace it if needed using the fuel line 791-181168.

Last updated: February 2026