🚗 Classic Fault — Mercedes-Benz W115 (1968–1976)
Hard start when cold — carburetor choke issue
💰 Estimated Repair Cost
$20 – $80 USD
Parts and labour estimate
🔧 Tools Required
Screwdrivers, choke thermometer, multimeter
📋 Overview
The W115 230.4 commonly fails to start on first or second attempt when cold, especially below 10C. The engine cranks normally but does not fire, or fires briefly then stalls. This is almost universally a choke-related issue on the twin Zenith 35/40 INAT carburetors.
🩺 Symptoms
- Engine cranks but does not fire when cold
- fires briefly then stalls
- requires multiple attempts to start
- excessive fuel smell during cranking
🔍 Possible Causes
- Stuck or incorrectly adjusted automatic choke
- choke pull-off diaphragm failure
- bimetal spring fatigue
- choke flap not closing fully
- old fuel mixture
🛠️ Diagnosis Steps
- Check choke flap position — should be nearly closed when cold.
- Test bimetal spring tension.
- Check choke pull-off diaphragm for cracks.
- Verify choke heater element resistance 40-60 ohms.
- Adjust choke if needed.
✅ Most Confirmed Fix
Replace choke pull-off diaphragm and re-adjust choke bimetal spring. Clean choke housing.
78% of users confirm this fix worked (14 reports)
🏷️ Parts Needed
Zenith 35/40 INAT choke pull-off diaphragm kit
🩺 Related Symptoms
🔗 Other Mercedes-Benz W115 Faults
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