Why does my Austin-Healey 3000 pop when cold or cut out when hot at idle?

Short answer: On a Healey 3000, popping when cold and stumbling hot at idle usually come down to the SU carburetors, valve lash or vacuum leaks. Check the oil dampers on top of each carburetor, make sure each metering needle is properly attached, set the valves, then tune the carbs. For a hot-idle miss, find the dead cylinder and spray carb cleaner around the throttle shafts to find leaks.

Symptom: Cold, it pops or backfires through the intake or exhaust. Hot, it stumbles, runs on three cylinders or dies at idle.

What to check first

1. Remove each SU damper cap and make sure the damper is topped up with the right oil.
2. Lift each piston and confirm the needle is attached and moves with it.
3. Check valve clearances against the manual.
4. With the engine idling, spray carb cleaner around the throttle shafts and listen for the idle to change.
5. Use an inductive timing light to find a dead cylinder and check the timing advance.

Likely causes

1. SU carburetor problems. The 3000 uses SU carburetors, which meter fuel with a needle on a sliding piston. The piston has an oil damper on top; if it's empty, or the needle isn't attached, the mixture goes wrong.
2. Valve clearance (lash) too tight. Valve lash is the small gap in the valve train. Too tight and valves may not seal fully, which can cause popping until the engine warms.
3. Vacuum leaks, often at worn throttle shafts. Worn carburetor throttle shafts let in extra air. That gives an uneven idle that changes as the engine warms.
4. Ignition timing or advance. A slow or stuck spark advance makes the engine run poorly. A timing light shows it.

What it usually costs

Owners in these threads didn't post prices.

Is it safe to keep driving?

A car that dies at idle in traffic is a nuisance and a risk on busy roads. A backfire through the carburetors can start a fire; keep an extinguisher handy and fix it before long drives.

DIY or shop?

All of this is classic hands-on work. SU tuning takes patience; a British car club or specialist can help.

Recalls, bulletins and complaints in plain words

• Recalls: NHTSA's recall and complaint lookups returned no data for this model in these years, which is normal for a car this old. NHTSA's database began in the 1960s, and there are no listings for this model there. Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• Plain words: The complaint count below shows how often owners reported problems that mention these words to NHTSA. A count is not proof of a defect.
• NHTSA complaints: 0 keyword-matched complaints for Austin-Healey 3000 1959–1967 (of 0 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-30; keywords: stall, backfire, carb, fuel) (NHTSA returned no data for 36 model-year queries). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In Austin Healey Engine Noise on Car Talk, a 1965 Healey 3000 with a freshly rebuilt engine popped and backfired cold and was fine after 10-15 minutes. Members suggested checking the SU dampers are nearly full of ATF and rechecking the valve adjustment. The owner adjusted the valves, then found one carburetor's metering needle wasn't attached; once secured and the carbs were tuned, it ran like a champ.
• In 1967 Austin Healey 3000 on Car Talk, a 1967 Healey 3000 ran great but cut out or ran on three cylinders when hot and idling at a light. Members suggested finding the dead cylinder with an inductive timing light, putting it on a scope, and checking for vacuum leaks, especially from worn SU throttle shafts, using carburetor cleaner sprayed around the shafts.

Quick tip

Before anything else, pull the damper caps and look. A missing needle or a dry damper is free to find and fixes a lot of SU headaches.

Vehicle focus: Austin-Healey 3000 (Mk I-III), 1959-1967, six-cylinder with SU carburetors.

Safety / mechanic note

Backfires and stalling are safety items. Verify with a mechanic.