Why is my outboard smoking so much?

Excessive smoke · Symptom: More smoke than normal.

Quick answer: Most often: normal briefly after fogging or during break-in (Tohatsu: double-oil break-in mix makes more smoke), 2-stroke oil mix too rich / oil injection fault, choke left on, poor carburetor adjustment, wrong spark plug. Start here: Note when and what colour: right after storage or break-in may be normal. If that doesn't fix it, work through the checks below, and see a marine mechanic if you're unsure.

Likely causes (most to least common)

Normal briefly after fogging or during break-in (Tohatsu: double-oil break-in mix makes more smoke)
2-stroke oil mix too rich / oil injection fault
Choke left on, poor carburetor adjustment, wrong spark plug
White steam = overheating or exhaust in cooling system
Blue smoke on 4-stroke = oil overfill or oil burning

Safe owner checks & fixes

Note when and what colour: right after storage or break-in may be normal.
Check 2-stroke mix ratio/oil level against the manual (never guess the ratio).
Push choke in once warm.
Check plugs (Discover Boating: black soot = rich or idling too long; white/blistered = too hot).
Check telltale stream; steam or alarm = see 07.
4-stroke: check oil level is not overfilled.

Parts / tools

Dipstick/oil per manual, correct 2-stroke oil, spark plugs per manual.

Call a marine mechanic when

Blue or white smoke persists after break-in/fogging; smoke with overheat or steam; oil level rising on a 4-stroke (fuel dilution) — compression test needed. If you're on the water and unsafe, call TowBoatUS/Sea Tow or the Coast Guard (VHF 16).

Sources

Values not stated here are model-specific; check your owner's manual.