Suzuki Outboard Troubleshooting: Won't Start, Stalls, Low Power, Vibration

Most Suzuki outboards that will not start have nothing wrong with them. The emergency stop lock plate is out, the shift lever is not in neutral, the fuel tank vent is closed, the hose is kinked or unplugged, or the starter was held too long and has cut out. Run the checklist below before you touch a tool. If the engine runs but will not rev past about 3000 r/min, that is not a fault either: a caution system has taken over, and the section on sudden speed drops tells you which one and what to do.

Everything here comes from Suzuki's own owner's manual troubleshooting tables and, for the next level of checks, the service manuals. Where the lists differ between the carbureted portables, the EFI motors and the remote and drive-by-wire models, the differences are shown rather than blended.

The 60-second checklist

1. Lock plate. On the DF8A/9.9A, DF9.9B/15A/20A and DF25A/30A the starter motor can operate with the lock plate out, but the engine cannot start. On the DF40A and up the starter will not operate at all without it. On the DF2.5 and DF4A/6A the manual's first check for a no-start is the lock plate.
2. Neutral. The recoil starter will not pull in gear, and on the DF4A/6A trying can damage it. Electric starters will not operate unless the shift lever or control handle is in neutral.
3. Fuel. Tank not empty, fuel not stale, tank air vent open, hose connected to the motor and not kinked or pinched. On a portable with a priming bulb, squeeze it until you feel resistance; on a DF2.5 or DF4A/6A running from the built-in tank, turn the fuel cock lever to the left and open the vent screw on the filler cap. A brand-new motor or a dry fuel line needs the tank filled and the line primed by several sharp pulls, or by the starter, before the normal procedure will work.
4. Choke. Carbureted portables (DF2.5, DF4A/6A, DF8A/9.9A) need the choke pulled fully out for a cold start and pushed back in afterward. The fuel-injected DF9.9B and up have no choke knob.
5. Fuse. A blown fuse is in the “starter motor will not operate” list for every electric-start family. Ratings and locations are in the fuse chart. Replace it only with the same type and rating; if the new one blows, the manuals say you may have a major electrical problem, so stop there.
6. Battery. Terminals corroded or loose, battery flat, or the sub-battery cable not connected on the larger motors. Most motors from the DF100A up carry a fuse in the sub-battery cable, and their manuals say the engine cannot be started if that cable is not correctly connected.
7. Starter time. Never hold the starter button or key for more than 5 seconds. If the engine fails to start after 5 seconds, wait 10 seconds and try again. On most motors from the DF40A up the starter's continuous operating time is set at five seconds and it stops by itself; wait about ten seconds for it to cool.

Starter motor will not turn

The owner's manual cause lists, verbatim, by family:

• DF8A/9.9A, DF9.9B/15A/20A, DF25A/30A: shift lever (or grip) is not in neutral; fuse is blown out (electric start model).
• DF40A/50A/60A, DF100A/115A/140A, DF150A/175A/200A (2020 manual), DF225/250: shift lever is not in neutral; fuse is blown out; emergency stop switch lock plate is not in position.
• DF75/90A: lock plate not in position; starter relay fuse blown; control handle not in neutral; battery terminal connection corroded or lost; battery power lost; starter motor failed; ignition switch or start/stop switch failed; electric wiring connection loose.
• DF115BG/140BG, DF150A/175A/200A (2023 manual), DF150AP/175AP/200AP, DF250AP/300AP and DF300B/350A: the same list, plus the sub battery cable fuse blown. On the DF115BG/140BG and DF300B/350A with the Keyless Start System, the switch line reads “engine switch or start/stop switch is failed” instead of ignition switch.

The DF150A/175A/200A is listed twice on this page because its 2020 and 2023 owner's manuals print different tables: the 2020 manual has the short lists, the 2023 manual the long ones. Check which you have.

Keyless Start System models have one more list, split by whether you hear the error beeps. If the system does not turn on when you operate the switch and the error sound is not heard, the manuals list: lock plate not in position; battery terminal connection corroded or lost; battery power lost; keyless control unit failure; electric wiring connection loose; and a failed remote control box (side mount), main panel (top mount) or engine switch panel. The DF100A/115A/140A, DF150A/175A/200A and DF150AP/175AP/200AP manuals (five short beeps, main switch) add one more: the main switch was operated continuously while communication with the key-fob was disabled. If the error sound is heard, the fob is the first suspect: outside the operating range, battery dead, in OFF mode, or not authenticated. After that the list is communication failure from strong radio waves or noise, a wiring connection failure or authentication error between the keyless control unit and the motor, or an abnormality in the engine's electronic control system. On the DF115BG/140BG, DF250AP/300AP and DF300B/350A the error sound is three short beeps and the switch is the engine switch. If the system will not turn off, the cause is a loose wiring connection or a failed remote control box, main panel or engine switch panel. Past the fob battery, this is dealer work.

The DF9.9B/15A/20A service manual splits the electric-start diagnosis by sound. No click from the magnetic switch: poor, loose or corroded battery connection, weak or shorted battery, defective neutral switch, blown fuse, defective starter button. Click but no cranking: weak or shorted battery, or battery voltage too low from deterioration; after that it is the starter itself. Motor spins but does not crank the engine: worn pinion, over-running clutch or ring gear teeth. Beyond the battery and its cables, that is dealer work.

One trap on the electric-start DF9.9B/15A/20A: a battery charge cutout system opens the charging circuit when battery voltage drops below 6 volts while the engine is running, and the starter motor will not operate while it is active. Check the battery and recharge it. Battery minimums by model are in the battery requirements chart.

Engine will not start, or is hard to start

• DF2.5: lock plate not in position; fuel tank empty; fuel hose kinked or pinched; spark plug fouled.
• DF4A/6A, DF8A/9.9A, DF9.9B/15A/20A, DF25A/30A: lock plate not in position; fuel tank empty; fuel hose not properly connected to the engine (on the DF6A with a separate tank); fuel hose kinked or pinched; spark plug fouled.
• DF40A/50A/60A, DF100A/115A/140A, DF150A/175A/200A (2020 manual), DF225/250: fuel tank empty; fuel hose not properly connected; fuel hose kinked or pinched; spark plug fouled.
• DF75/90A, DF115BG/140BG, DF150A/175A/200A (2023 manual), DF150AP/175AP/200AP, DF250AP/300AP, DF300B/350A: fuel tank empty; fuel deteriorated; starting procedure not correct; fuel tank air vent not opened; hose not connected; hose kinked or pinched; fuel filter clogged; fuel pump failed; fuel tank filter clogged; spark plug fouled; ignition system fouled; wiring connection loose.

Work the list top to bottom. A fouled plug sits at or near the bottom of every list; it is often the result of the others, not the cause. Plug numbers and gaps are in the spark plug chart.

The DF9.9B/15A/20A and DF70A to DF100B service manuals add the EFI next level. Fuel not reaching the delivery pipe: clogged, bent or badly routed fuel hose, low- or high-pressure fuel pump failure, injector failure, wiring connection failure. Cranks with no or weak spark: loose or disconnected lead wire, spark plugs, ignition coil, CKP or CMP sensor, and on the DF9.9B family the power source coil, emergency stop switch and neutral switch; on the DF70A family a blown ignition-system fuse comes first. Past the plug, fuses and connectors that needs a meter and usually the SDS tool. If a diagnostic code is flashing, start with the diagnostic codes page.

Two emergency-start notes. An emergency starter rope is not provided with the electric-start DF9.9B/15A/20A. On the DF40A/50A/60A and DF75/90A, if the battery voltage is too low to run the electric fuel pump, rope-starting will not work because fuel will not reach the engine.

Idles rough or stalls

• DF2.5, DF4A/6A, DF8A/9.9A: choke knob not pushed in securely; fuel hose kinked or pinched; spark plug fouled.
• DF9.9B through DF60A, DF100A/115A/140A, DF150A/175A/200A (2020 manual), DF225/250: fuel hose kinked or pinched; spark plug fouled.
• DF75/90A, DF115BG/140BG, DF150A/175A/200A (2023 manual), DF300B/350A and the AP models: spark plug fouled; fuel hose kinked, pinched or not properly connected; fuel deteriorated; fuel filter clogged; fuel pump failed; ignition system fouled; incorrect engine oil used; thermostat failed; wiring loose.

Oil grades by model are on the oil capacity chart. If the motor stalls only when you shift into gear, the DF9.9B service manual points at idle speed set too low, or propeller shaft bearings that are damaged, dry or seized. On remote-control models from the DF25A up, a stall for any reason sounds the caution buzzer three times; that is a notice, not a fault code.

The service manual list for unstable idling on the EFI motors (MAP sensor vacuum passage, TPS, IAC system, fuel pressure, injector, IAT sensor, ECM, plug, coil) is SDS-tool work. Before any of it, the DF70A manual says to make sure there is no self-diagnostic code showing.

Will not reach full throttle, or power is low

• DF2.5, DF4A/6A, DF8A/9.9A: engine is overloaded; propeller is damaged; propeller is not properly matched to loads.
• DF9.9B through DF60A, DF100A/115A/140A, DF150A/175A/200A (2020 manual), DF225/250: the same three plus “caution/diagnosis system is activated” (see the next section).
• DF75/90A, DF115BG/140BG, DF150A/175A/200A (2023 manual), DF300B/350A and the AP models: propeller damaged, not clean, or not properly selected; outboard not correctly installed; trim angle not properly adjusted; spark plug fouled or incorrectly selected; fuel hose kinked; fuel filter clogged; fuel deteriorated; fuel pump failed; ignition system failed; electronic throttle system failed; heavy cargo on the boat; water has entered the boat; bottom of boat not clean or damaged.

The prop rule from the installation manuals: select a propeller that lets the engine reach the recommended operating range at full throttle with the maximum boat load. A tachometer at full throttle tells you whether you are propped right; the ranges and the method are in the full-throttle RPM and propeller guide. If the motor revs freely but the boat does not go, the DF9.9B service manual lists a slipping propeller bush, a bent or worn propeller, a failed bush, or a bent driveshaft or propeller shaft; the DF75/90A, DF115BG/140BG, DF150A/175A/200A (2023 manual), DF300B/350A and AP manuals put “propeller is not rotated” down to a worn propeller bush or a damaged drive or propeller shaft. The drive-by-wire manuals print one more row: if the shift will not engage at all, the DF115BG/140BG, DF150AP/175AP/200AP and DF250AP/300AP give one cause, a failed electronic shift control system, and the DF300B/350A adds a broken or detached shift link. Neither is something to fix on the water; that is dealer work. Ventilation, where the prop grabs air and rpm spikes, is one of the over-revolution causes the DF4A/6A manual names: cavitation when turning hard, a propeller with a slipping bush or worn blades, or a trim setting that is too high.

Engine speed suddenly drops to about 3000 r/min

This is the over-revolution caution. It activates when engine speed exceeds the maximum recommended speed for more than 10 seconds, then holds the motor at approximately 3000 r/min. On most families the REV LIMIT or caution lamp lights; on the DF25A/30A the caution lamp does not light and only the remote-control buzzer beeps. Reset by moving the throttle to idle for about one second, or about four seconds on the DF25A/30A. If it activates for no apparent reason, the manuals say to consult your authorized Suzuki marine dealer. The DF4A/6A have a limiter but no lamp: the motor runs rough above 5100 r/min (DF4A) or 5850 r/min (DF6A) and you reduce speed.

Two other cautions also limit speed, and they need action, not a reset. The limits below are from the owner's manuals; the overheat behaviour is covered in full in why your outboard is overheating.

Oil pressure: the OIL lamp lights (or the gauge shows “Low Oil Pressure”), the buzzer beeps, and if you keep running the engine stops itself 3 minutes after the caution began. Stop immediately if wind and water conditions make it safe, check the oil level and add oil if necessary; if the level is correct, consult your dealer. The DF8A/9.9A manual gives the speed limit but states no automatic stop; every other family in the table stops after 3 minutes. Which lamp means what, and the low-battery caution on the DF40A and up, are in the warning light and buzzer guide.

Engine vibrates excessively

• DF2.5: clamp screws loose; foreign object (seaweed etc.) tangled on the propeller; propeller damaged.
• DF4A/6A through DF60A, DF100A/115A/140A, DF150A/175A/200A (2020 manual), DF225/250: engine mounting bolts or clamp screws loose; foreign object tangled on the propeller; propeller damaged.
• DF75/90A, DF115BG/140BG, DF150A/175A/200A (2023 manual), DF300B/350A and the AP models: propeller damaged; engine mounting bolts or clamp screws loose.

Tilt up and look at the prop first, then check the clamp screws and transom bolts; the mounting torques by family are in the mounting guide. A vibration that stays after a new prop is, per the DF9.9B service manual, a slipping or failed propeller bush, a bent or worn propeller, or a bent driveshaft or propeller shaft.

Engine overheats

The owner's manual list is short: cooling water intakes blocked; engine overloaded; propeller not properly matched to loads. That row is in the manuals that print the short lists above (DF2.5 through DF60A, DF100A/115A/140A, the 2020 DF150A/175A/200A and DF225/250). The manuals with the long lists (DF75/90A, DF115BG/140BG, 2023 DF150A/175A/200A, DF300B/350A and the AP models) have no overheat row; their “caution system is activated” list starts with a clogged cooling water passage, a failed thermostat and a failed water pump. Check the pilot water hole, clear the intakes, and read the full procedure, the impeller and thermostat intervals and the temperature thresholds in why your outboard is overheating.

Before you call the dealer

Write down what the motor did, what the lamps and buzzer did, the hours on the motor (a monitor-tachometer shows total hours for three seconds at key-on) and, if the CHECK ENGINE lamp was flashing, the code count from the diagnostic codes page. The self-diagnostic codes stay in the ECM memory even if the battery is disconnected, so the dealer can read them later. The manuals' standing instruction is that if a caution system activates while you are operating, stop the motor as soon as possible and correct the problem or consult your authorized Suzuki marine dealer. If the motor is under warranty, check with your dealer before opening anything beyond the plugs, fuses and filters.

Parts for this job

For the checks above you need NGK spark plugs for your model, a low-pressure fuel filter, and fresh fuel treated with fuel conditioner. Fuses, switches and starter parts are in electrical and ignition parts, and propellers in Suzuki genuine propellers. Boat Max Online is an authorized Suzuki, Honda and Yamaha dealer selling outboards up to 30 hp; orders over $149 ship free to the lower 48.

Sources: Suzuki owner's manuals for DF2.5, DF4A/6A, DF8A/9.9A, DF9.9B/15A/20A, DF25A/30A, DF40A/50A/60A, DF75/90A, DF100A/115A/140A (2016, 99011-90J70-03B), DF115B/140B (2023) and DF115BG/140BG (2022–2023, 99011-99L20-03B), DF150A/175A/200A (2020; 2023, 99011-96LM0-03B), DF150AP/175AP/200AP, DF225/250, DF250AP/300AP and DF300B/350A (2023, 99011-98L60-03B); Suzuki service manuals 99500-89L00-01E (DF9.9B/15A/20A) and 99500-87L10-01E (DF70A/80A/90A/100B); Suzuki installation manuals for DF70A/90A and DF115A/140A. Figures are Suzuki's published values; confirm against the manual for your model year and serial number.