Craftsman 316791940 trimmer Parts

On the Craftsman gas line trimmer model 316791940, you replace the trimmer line by removing the old line, reinstalling the line glide plate, then feeding a new length of line through the correct holes in the cutting head. Follow the hole and arrow guidance shown in the 316791940 owner's manual.

Quick steps (Hassle-Free cutting head)

• Shut the engine off and let the cutting head stop completely.
• Remove the old line and remove the line glide plate from the cutting head.
• Clean the cutting head so the line feeds smoothly.
• Reinstall the line glide plate and align its arrow correctly:
  • A: for medium (red) or large (black) line
  • B: for smaller-than-medium line
• Insert both ends of the new line through the proper holes in the side of the cutting head.
• Confirm the line length is controlled by the string cut-off blade (do not alter that blade).

Important safety and fit notes

• Do not remove or alter the line cutting blade assembly; excessive line length can overheat the clutch and damage the unit.
• Do not remove the cutting head from the trimmer just to replace line (this model is designed for line replacement with the head installed).
• Use the line size intended for the job (grass vs. heavier weeds) and match the glide plate arrow position to the line diameter.

Arrow position guide

What you are installing	Glide plate arrow position	Why
Medium (red) or large (black) line	A	Keeps feed path aligned for thicker line
Smaller-than-medium line	B	Prevents binding and poor feeding

Why it matters

Correct glide plate alignment and using the proper holes prevents line binding, reduces vibration, and protects the clutch from overheating. It also helps the head feed consistently so trimming and edging stay smooth.

Last updated: February 2026

When a Craftsman gas line trimmer model 316791940 dies as you squeeze the throttle, the engine is usually running too rich or starving for air or fuel under load. The fastest fixes are cleaning or replacing the air filter, checking the spark plug, and confirming fresh fuel and correct starting settings per the 316791940 owner's manual.

Quick checks that fix most “dies when I give gas” problems

• Inspect the air filter; if it is dirty or oil-soaked, replace it with the correct engine air filter 753-05254.
• Check the spark plug condition and gap; replace a fouled plug with the correct spark plug 794-00082.
• Use fresh fuel (old fuel causes bogging and stalling when accelerating).
• Make sure the primer bulb and cold-start lever are used correctly for starting, then moved to the run position.
• Verify the throttle trigger moves freely and returns smoothly.
• Look for debris packed around the cutting head and shield; heavy drag can pull RPM down.

What to look for (symptom-to-cause guide)

What you notice	Most likely cause	What we recommend
Starts, idles, then dies when throttled	Clogged air filter or fouled spark plug	Replace engine air filter 753-05254 and/or spark plug 794-00082
Dies only after warming up	Restricted airflow, dirty plug, or exhaust restriction	Check filter and plug first; inspect muffler area for carbon buildup
Bogging plus fuel smell	Running rich (too much fuel)	Replace air filter; verify choke is fully off in run
Stalls when line head contacts grass	Excess load or debris around head/shield	Clear debris; trim in lighter passes

Why it matters

A trimmer that stalls on acceleration is usually not getting the right air-fuel mix at higher RPM. A clogged air filter can make the engine run overly rich, foul the spark plug, and cause stalling when you “give it gas.”

Safety note before servicing

Stop the engine and disconnect the spark plug before maintenance or repair, as outlined in the 316791940 owner's manual.

Last updated: February 2026

If your Craftsman 316791940 gas line trimmer is flooded, clear the excess fuel by opening the throttle fully and pulling the starter until it fires, then let it run briefly to dry out. If it still will not start, dry the spark plug and check the air filter.

Quick steps to unflood it

• Move the trimmer to a well-ventilated area and set it on the ground.
• Set the switch to ON.
• Hold the throttle fully open (wide open throttle).
• Pull the starter rope repeatedly until the engine sputters or starts.
• Once it starts, keep it running at a fast idle for 20 to 30 seconds to clear remaining fuel.
• If it will not fire after several pulls, remove and dry the spark plug, then try again.

If it still will not start

A flooded engine often has a wet spark plug or restricted airflow. Use this checklist before you keep pulling.

What to check	What you are looking for	What to do
Spark plug condition	Wet, fuel smell, heavy carbon	Dry/replace and set gap to 0.025 in. (0.635 mm)
Air filter	Dirty or soaked	Clean or replace
Fuel quality	Old gas (over 60 days)	Drain and refill with fresh fuel

Parts that commonly solve flooding-related no-starts

• Lawn & garden equipment spark plug 794-00082: Replace if fouled, cracked, or repeatedly wet.
• Air filter (listed for this model): Replace if dirty or fuel-soaked.

Why it matters

Flooding prevents the spark plug from igniting the air-fuel mix. Clearing the cylinder and restoring airflow gets the mixture back into a range the ignition system can light, which reduces hard starting and plug fouling.

For model-specific starting and maintenance details (including spark plug service and storage fuel guidance), follow the 316791940 owner's manual.

Last updated: February 2026

For the Craftsman line trimmer model 316791940, use unleaded gasoline and the correct 2-cycle oil mixed at 40:1 (2.5%) for the fuel mix; for the crankcase (if your unit has an oil-fill system), use SAE 30 oil. Confirm the exact fuel and oil instructions in the 316791940 owner's manual.

Fuel mix: what to use

• Gas: fresh, unleaded gasoline
• 2-cycle oil: quality 2-stroke engine oil intended for air-cooled small engines
• Mix ratio: 40:1 (gasoline to 2-cycle oil)
• Freshness: do not use gasoline stored more than 60 days
• Storage tip: run the engine until it stalls after draining the tank to clear fuel from the carburetor

Quick mix table (40:1)

Gasoline amount	2-cycle oil to add
1 gallon	3.2 fl oz
1/2 gallon	1.6 fl oz
1 quart	0.8 fl oz

Engine oil (SAE 30): when it applies

Some versions of this 25cc platform specify SAE 30 as the engine lubrication oil and list a 3.04 oz (90 ml) crankcase oil capacity. Use the oil fill plug location and service steps shown in the 316791940 owner's manual to verify whether your specific unit uses crankcase oil and how to check or change it.

Why it matters

Correct fuel and lubrication prevents hard starting, plug fouling, overheating, and premature wear on key components like the ignition system and muffler. If the trimmer starts but runs poorly, a tune-up with a fresh plug and clean air filter often restores performance.

Parts that commonly help with fuel-related running issues

Symptom	Common maintenance item	Example model-matched part
Hard starting, misfire	Spark plug	Lawn & garden equipment spark plug 794-00082
Runs rich, lacks power	Air filter	Mtd lawn and garden equipment engine air filter 753-05254

Last updated: February 2026

For the Craftsman gas line trimmer model 316791940, fuel line size is determined by the fitting and grommet diameters on your specific unit. Most small-engine trimmers use fuel tubing in the 1/8 in to 3/16 in outside diameter range; confirm the exact size by measuring your old line and checking the fuel system diagram in the 316791940 owner's manual.

How to get the correct fuel line size (works every time)

• Remove the air filter cover so you can see the carburetor fuel nipples.
• Pull the old line out and cut a clean, square end.
• Measure inside diameter (ID) to match the carburetor nipple snugly.
• Measure outside diameter (OD) to match the tank grommet pass-through.
• If your trimmer uses two lines (supply and return), measure both; they can be different.
• Replace the fuel filter in the tank if it is restricted or falling apart.

Typical sizes you will see on 4-cycle trimmers

Common use	Typical ID	Typical OD
Small supply/return line	3/32 in to 1/8 in	1/8 in to 3/16 in
Larger return/vent line (some setups)	1/8 in	3/16 in

Signs the fuel line is the wrong size

• Hard starting or stalling (air leak at the carburetor nipple)
• Fuel seepage at the tank grommet
• Line pops off under vibration
• Primer bulb does not fill or stays collapsed

Why it matters

Correct ID and OD prevent air leaks and fuel starvation. A line that is too tight can split; a line that is too loose can leak and cause surging, poor acceleration, or no-start.

Last updated: February 2026