The Suzuki DF9.9B, DF15A and DF20A are the same engine. The owner's manual gives all three one specification block: two cylinders, 327 cm³ (20.0 cu in), 60.4 × 57 mm (2.38 × 2.24 in) bore and stroke, 1.0 L of engine oil, the same spark plug, the same fuses and the same battery requirement. The service manual adds that they share a 12:25 (2.08) gear ratio, the same propeller list and the same weights variant for variant. What separates them is the tune in the ECM: maximum output of 7.3 kW (9.9 PS), 11.0 kW (15 PS) and 14.7 kW (20 PS), full-throttle ranges of 4700–5700, 5000–6000 and 5300–6300 r/min, a different rev limiter and a different ignition-timing range.
Two things follow from that. A DF20A weighs exactly what a DF9.9B weighs in the same configuration, so the extra horsepower costs nothing in weight; the only reasons to buy less are a hull capacity rating, a lake rule, or price. And the maintenance items in the manuals (oil, filter, plug, gear oil, impeller, thermostat, battery) are identical across the three, so a service kit or how-to written for one applies to the others.
Spec table: DF9.9B vs DF15A vs DF20A
Figures are from the 2020 owner's manual (99011-89LA0-03B) and the service manual (99500-89L00-01E with its supplements). Where the two print a figure differently, both are shown.
| Specification | DF9.9B | DF15A | DF20A |
|---|---|---|---|
| Maximum output | 7.3 kW (9.9 PS) | 11.0 kW (15 PS) | 14.7 kW (20 PS) |
| Full-throttle operating range | 4700–5700 r/min | 5000–6000 r/min | 5300–6300 r/min |
| Over-revolution limiter (service manual, serial 310001 and later) | 5900 r/min | 6200 r/min | 6300 r/min |
| Over-revolution limiter (service data, serial 910001 and later) | 5800 r/min | 6100 r/min | 6400 r/min |
| Ignition timing range | 5°–14° BTDC | 5°–10° BTDC | 5°–20° BTDC |
Everything else in the specification is shared:
| Specification | DF9.9B, DF15A and DF20A |
|---|---|
| Idle speed (neutral) | 850 ± 50 r/min |
| Engine | 4-stroke SOHC, 2 cylinders |
| Displacement | 327 cm³ (20.0 cu in owner's manual; 19.9 cu in service manual) |
| Bore × stroke | 60.4 × 57 mm (2.38 × 2.24 in) |
| Compression ratio | 10.5 : 1 |
| Gear ratio | 12 : 25 (2.08) |
| Engine oil capacity | 1.0 L (1.1/0.9 US/Imp qt) oil change only; 1.1 L (1.2/1.0 US/Imp qt) with filter change |
| Gear oil capacity | Approx. 0.25 L (0.26/0.22 US/Imp qt) |
| Spark plug | NGK MR6K-9 (2020 manual; serial 910001 and later); NGK CPR6EA-9 (2014 manual and earlier serials); gap 0.8–0.9 mm (0.031–0.035 in) |
| Battery charge coil output | 72 W (12 V 6 A at 5000 r/min) manual start; 144 W (12 V 12 A at 3000 r/min) electric start |
| Transom height (tiller and R models) | S 422 mm (15 in type); L 549 mm (20 in type) |
| Transom height (power tilt T/TH models) | S 426 mm (15 in); L 553 mm (20 in); X 680 mm (25 in) on DF9.9BT/BTH only |
| Propeller sizes (service manual) | 3 × 9¼ × 7, 8, 9, 10, 11 in; 12 in pitch and a 4 × 10 × 7 added in the 2018 specification |
The service manual's 2024 specification (serial 440001 and later) prints the DF9.9B oil capacity as 1.10 L for an oil change and 1.10 L for an oil-filter change, so check your manual if your motor is that new.
What actually changes
Output and full-throttle range
Each model has its own full-throttle operating range, and that range is what you prop to. Suzuki's instruction is to select a propeller that lets the engine reach the recommended range at full throttle with the maximum boat load; a prop with too much or too little pitch gives an incorrect maximum engine speed and can damage the motor. The three motors share the same prop list, so the difference is which pitch lands you in range: the same hull and load will typically take a lower pitch on the DF9.9B than on the DF20A. The method is on our full-throttle RPM and propeller guide, and the sizes are on the Suzuki propeller chart.
Rev limiter, by serial number
The over-revolution limiter is set per model in the ECM, and Suzuki has changed it across serial ranges. The owner's manual describes the caution as activating when engine speed exceeds the maximum recommended speed for more than 10 seconds; the engine is then reduced to approximately 3000 r/min with the caution lamp lit.
| Serial range (service manual) | DF9.9B | DF15A | DF20A |
|---|---|---|---|
| Main manual (DF15A/DF20A only, before 310001) | not listed | 6200 r/min | 6300 r/min |
| 310001 and later (adds DF9.9B); same in the 410001 power-tilt data | 5900 r/min | 6200 r/min | 6300 r/min |
| 910001 and later (2018 data, repeated in the 2024 data) | 5800 r/min | 6100 r/min | 6400 r/min |
When the limiter acts, engine speed is reduced to approximately 3000 r/min by an intermittent fuel-injection signal and the caution lamp lights. Close the throttle to bring the engine below approximately 3000 r/min for one second and it resets. In neutral the limit is 3000 r/min and the lamp does not light. Our warning light and buzzer guide covers the rest of the caution system.
Ignition timing
All three idle on the same timing, approximately 5° BTDC at 1000 r/min in neutral. Under load the ECM advances within a range that differs by model: 5°–14° BTDC on the DF9.9B, 5°–10° on the DF15A and 5°–20° on the DF20A. The ECM controls it; the service manual has ignition timing inspected every 200 hours (12 months).
What does not change
- Engine oil: SAE 10W-40 or 10W-30 Suzuki Marine 4-Cycle Engine Oil (ECSTAR); 1.0 L for an oil change. Change at the initial 20 hours (1 month), then every 100 hours (12 months); replace the filter at 20 hours and then every 200 hours. See the DF9.9B/15A/20A oil change how-to.
- Gear oil: approx. 0.25 L of Suzuki Hypoid Gear Oil or SAE 90 hypoid rated API GL-5.
- Spark plug: one plug type across the three, by serial (table above); resistor type only.
- Water pump impeller: inspect at 200 hours, replace every 300 hours (36 months). Thermostat: 48–52 °C (118–126 °F) opening, inspect every 100 hours (12 months).
- Battery (electric start): 450 MCA, or 330 CCA, or 70 RC minutes minimum; a 12 V 35 AH battery, rectifier and related items are needed for accessories on a recoil-start model; do not use a deep-cycle battery as the main cranking battery. See which battery for a 9.9, 15 or 20.
- Fuses (electric start): 30 A main, 10 A ECM.
- Propeller nut: 16–20 N·m (12–15 lb-ft) in the 2020 owner's manual; the service manual specifies 18 N·m (13.0 lbf-ft).
Variants: reading the model code
The suffix after the model number tells you the configuration. E is electric start on a tiller motor; R is remote control with manual tilt; T is remote control with power tilt; TH is a tiller motor with power tilt. The 2020 owner's manual covers DF9.9B/BE/BR/BT/BTH, DF15A/AE/AR/ATH and DF20A/AE/AR/AT/ATH. Weights below are from the service manual, without engine oil.
| Variant | S (15 in) | L (20 in) | X (25 in) |
|---|---|---|---|
| DF9.9B, DF15A, DF20A (tiller, manual start) | 44 kg (97 lb) | 45 kg (99 lb) | — |
| DF9.9BE, DF15AE, DF20AE (tiller, electric start) | 48 kg (106 lb) | 49 kg (108 lb) | — |
| DF9.9BR, DF15AR, DF20AR (remote, manual tilt) | 47 kg (104 lb) | 48 kg (106 lb) | — |
| DF9.9BT (remote, power tilt) | 52.5 kg (115.7 lb) | 54.5 kg (120.2 lb) | 57.0 kg (125.7 lb) |
| DF9.9BTH (tiller, power tilt) | 53.5 kg (117.9 lb) | 55.5 kg (122.4 lb) | 58.0 kg (127.9 lb) |
| DF15ATH (tiller, power tilt) | — | 55.5 kg (122.4 lb) | — |
| DF20AT (remote, power tilt) | 52.5 kg (115.7 lb) | 54.5 kg (120.2 lb) | — |
| DF20ATH (tiller, power tilt) | — | 55.5 kg (122.4 lb) | — |
Other differences between configurations, from the service manual:
- Length: a tiller motor is 662 mm (26.1 in) front to back; a remote (R) motor is 609 mm (24.0 in).
- Tilt: manual-tilt motors have a 0–16° trim range with 5 tilt-pin positions and a 73° maximum tilt. Power-tilt motors have a 0–12° trim range, 4 pin positions and a 66° maximum tilt.
- T models and the sub-battery cable: Suzuki's set-up manual says not to connect the sub-battery cable to the remote harness; doing so blows the sub-battery fuse. See the battery cable and wiring guide.
A tiller DF9.9B/15A/20A can be converted to remote control with the tiller-to-remote conversion kit.
DF9.9A vs DF9.9B: not the same motor
Suzuki has sold two different 9.9 hp four-strokes with different specifications, so do not assume a part or procedure for one applies to the other. The DF9.9A shares its engine with the DF8A; the DF9.9B shares its engine with the DF15A and DF20A. The model and identification numbers are stamped on a plate on the clamp bracket, so check there before ordering anything.
| DF9.9A (with DF8A) | DF9.9B (with DF15A/DF20A) | |
|---|---|---|
| Engine | 2 cylinders, 208 cm³ (12.7 cu in), 51 × 51 mm (2.00 × 2.00 in) | 2 cylinders, 327 cm³ (20.0 cu in), 60.4 × 57 mm (2.38 × 2.24 in) |
| Fuel system | Carburetor, with choke knob, carburetor drain screw and (DF9.9A) an accelerator pump | Electronic fuel injection with ECM |
| Ignition | Suzuki PEI | Digital CDI |
| Maximum output | 7.3 kW (9.9 PS) | 7.3 kW (9.9 PS) |
| Full-throttle range | 5200–6200 r/min | 4700–5700 r/min |
| Idle speed (neutral) | 950 ± 50 r/min | 850 ± 50 r/min |
| Engine oil capacity | 0.8 L (0.85/0.70 US/Imp qt) | 1.0 L (1.1/0.9 US/Imp qt) |
| Spark plug | NGK CR6E, gap 0.7–0.8 mm (0.028–0.031 in) | NGK MR6K-9 (earlier CPR6EA-9), gap 0.8–0.9 mm (0.031–0.035 in) |
| Gear oil | Approx. 250 ml (8.5/8.8 US/Imp oz) | Approx. 0.25 L (0.26/0.22 US/Imp qt) |
| Gear ratio | 12 : 25 (2.08) | 12 : 25 (2.08) |
| Diagnostic system and oil-change reminder | None in its owner's manual | Caution lamp with over-rev, oil-pressure and overheat cautions, oil-change reminder and diagnostic codes |
| Propeller nut torque (owner's manual) | 16–20 N·m (12–14 lb-ft) | 16–20 N·m (12–15 lb-ft) |
The DF9.9A has its own DF8A/DF9.9A service guide on this blog; both families are on our oil capacity chart and spark plug chart.
Which one to buy
- Tender or dinghy: weight is the same for all three in a given configuration, so choose by the hull's capacity plate, not by what you can lift. The DF9.9B exists for hulls and waters limited to 9.9 hp; if the plate allows 15 or 20, take it. Our post on what size outboard your boat needs covers the rating.
- Jon boat or small skiff: the DF20A at 14.7 kW is the same engine working in its 5300–6300 r/min range; on a loaded boat that extra output is where you notice the difference.
- Sailboat auxiliary: the 25 in (X, 680 mm) transom height is listed only for the DF9.9BT/BTH power-tilt models. Measure first: how to measure for shaft length.
- Tiller or remote: an R motor is 609 mm long against 662 mm for a tiller motor. Electric-start motors need a battery that meets the spec above.
Whichever you pick, the first 10 hours are a break-in period; the procedure is in our break-in guide.
Parts for these motors
Boat Max Online is an authorized Suzuki, Honda and Yamaha Marine dealer and sells complete Suzuki outboards up to 30 hp, with free shipping on motors and on orders over $149 to the lower 48. Shop all three in our Suzuki outboards collection, and the oil change kit, water pump repair kit, 48–52 °C thermostat and genuine Suzuki propellers that fit them.
Sources: Suzuki owner's manuals for DF9.9B/DF15A/DF20A (99011-89LA0-03B, 2020 and 99011-89L12-03B, 2014) and DF8A/DF9.9A (99011-99J40-03B); Suzuki service manuals 99500-89L00-01E (DF9.9B/15A/20A, with supplements 99501-89L00-01E, 99501-89L10-01E and 99501-89L20-01E) and 99500-99J00 (DF8A/9.9A); Suzuki set-up manual 99505-89L10-01E. Figures are Suzuki's published values; confirm against the manual for your model year and serial number.