Why is there gas in the oil on my Triumph TR6?

Short answer: Gas in a TR6's oil usually means fuel is getting past the carburetor float valves, a fuel-soaked float, too much pump pressure, or a torn mechanical fuel pump diaphragm. A dead cylinder can do it too. Change the oil right away, because thinned oil doesn't protect the bearings.

Symptom: The dipstick smells of gasoline, the oil level climbs, or the oil looks thin.

What to check first

1. Smell the oil and compare the level with a known reading; rising level means fuel is getting in.
2. Pull each carburetor float bowl and check the float for fuel inside it and the needle for wear.
3. If an electric pump was added, measure fuel pressure; carbureted TR6s need low pressure.
4. Check the mechanical fuel pump for a torn diaphragm.
5. Check that every cylinder fires (pull plug wires one at a time or check plug color).

Likely causes

1. Carburetor float needle or seat leaking. The float valve in each Zenith-Stromberg carburetor shuts off fuel when the bowl is full. If it leaks, extra fuel floods the engine and washes into the oil.
2. Fuel-damaged floats. Older cork or brass floats can soak up fuel or leak and sink, so the valve never closes.
3. Too much pressure from an electric fuel pump. An add-on electric pump can push past the float needles. These carburetors want low pressure.
4. Mechanical fuel pump diaphragm torn. A torn diaphragm in the engine-driven pump can leak fuel straight into the crankcase.
5. Ignition miss. A cylinder that doesn't fire leaves raw fuel to run down the cylinder walls into the oil.

What it usually costs

The threads didn't include prices. Float needle kits and floats are inexpensive; a fuel pump or rebuilt carburetors cost more. Get a quote from a British-car shop.

Is it safe to keep driving?

Fuel-diluted oil can wipe out engine bearings and is a fire risk if fuel is also leaking outside. Change the oil and find the cause before driving much.

DIY or shop?

Float and needle work is a classic owner job with a manual. Fuel pump diaphragm and ignition checks are manageable; a specialist helps with carburetor tuning.

Recalls, bulletins and complaints in plain words

• Related recalls: NHTSA lists these Triumph recalls in these years: 70V006000 (1969-1970, fuel filler pipe and cap); 74V111000 (1969-1974, fuel tank assembly); 78V014000 (1973-1976, throttle linkage might not close fully, so the engine speed may not drop). Check your VIN at nhtsa.gov/recalls. These are very old campaigns; ask a Triumph club whether yours had them done.
• Plain words: None of these recalls is about fuel in the oil, but the fuel tank and throttle linkage items are worth checking on any TR6.
• NHTSA complaints: 0 keyword-matched complaints for Triumph TR6 1969–1976 (of 2 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-28; keywords: fuel, oil, carb, start, leak). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In Gas in the engine Triumph TR6 on Car Talk, a TR6 owner found the oil smelling of gas even after rebuilding the carburetors. Members listed float bowl needles and seats, floats damaged by ethanol fuel, too much pressure from an electric pump, a misfiring cylinder and a leaking mechanical fuel pump diaphragm, and said to change the diluted oil right away.
• In Correct tire pressure 1974 TR6 52000mi on Car Talk, a 1974 TR6 owner asked about tire pressure. Members said the original 185R15 tires were set around 20 psi front and 24 rear, that modern tires should match the load rating, and the owner settled on 24/28 psi.

Quick tip

Change the oil first, then go straight to the float needles. That's where most fuel-in-oil cases on carbureted cars start.

Vehicle focus: Triumph TR6, 1969-1976 (US carbureted models).

Safety / mechanic note

Fuel in the oil and fuel leaks are fire and engine-damage risks. Verify with a mechanic.