🚗 Classic Fault — Mercedes-Benz W115 (1968–1976)
Zenith 35/40 INAT accelerator pump diaphragm split
💰 Estimated Repair Cost
$10 – $35 USD
Parts and labour estimate
🔧 Tools Required
Screwdrivers, inspection mirror
📋 Overview
The accelerator pump diaphragm in the Zenith 35/40 INAT carburetors splits or hardens with age. The result is no fuel squirt on throttle opening, causing a flat spot or momentary stall when accelerating from low speed.
🩺 Symptoms
- Stumble or hesitation on acceleration from idle
- engine almost stalls then recovers
- worse when warm
🔍 Possible Causes
- Hardened or split accelerator pump diaphragm
- blocked accelerator pump jet
- worn pump rod linkage
🛠️ Diagnosis Steps
Remove air filter. Observe carb throat while snapping throttle open — there should be a visible squirt of fuel. No squirt confirms pump failure.
✅ Most Confirmed Fix
Replace accelerator pump diaphragm. Clean pump jet passage.
87% of users confirm this fix worked (34 reports)
🏷️ Parts Needed
Zenith accelerator pump diaphragm repair kit
🔗 Other Mercedes-Benz W115 Faults
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