Suzuki DR650 starts cold but dies when hot at traffic lights

I would separate fuel from ignition first. When it dies hot, immediately open the fuel cap and listen for vacuum. A blocked tank vent can look exactly like fuel starvation.

Check the idle speed when fully warm too. On my old single it sounded fine cold, but once hot it was set too low and the engine had no margin when the fan/charging load changed.

Does it cough before it stops or does it cut like a switch? A cough and slow fade usually points me toward mixture or fuel flow. A clean sudden stop makes me suspicious of coil, pickup or wiring.

I tried opening the fuel cap when it stalled and there was no hiss. It does not cut like a switch. The idle gets uneven, then it quits. If I hold a little throttle it survives, but it feels rough.

Diagnosis plan: warm idle failure on a DR650

Mark, your extra detail is important: the engine fades, becomes irregular, and can be kept alive with a little throttle. That makes an instant electrical failure less likely and moves the first checks toward idle circuit, air leak, valve clearance, and hot mixture behavior.

Here is the sequence I would use in the workshop.

1. Confirm the base idle speed fully hot. Do not set idle on a cold engine. Ride until the cylinder head and oil are genuinely warm, then set the idle to the manufacturer range. If it is too low, a big single-cylinder engine can stall even when nothing is broken.
2. Inspect the intake boots. Look between carburetor, cylinder head and airbox. Any cracked rubber, loose clamp or poorly seated boot can create a lean condition that becomes worse at hot idle. Spray testing must be done carefully and away from ignition sources; safer is a visual inspection plus checking whether the idle changes when you gently move the carb body.
3. Clean the pilot circuit, not only the float bowl. Draining the bowl removes water or sediment, but it does not clean the pilot jet. A partly restricted pilot jet often allows cold running with choke/enrichment, then fails when the bike is hot and the enrichment is off.
4. Check fuel height. A float level that is slightly low can show up first at idle and low throttle. Measure it instead of guessing.
5. Verify valve clearance. Tight intake valves can reduce hot compression and make idle unstable. This is a classic reason a motorcycle starts cold but becomes difficult once hot.
6. Only then chase ignition. If the symptom changes into an instant cut, test coil resistance hot and cold, inspect connectors, and check pickup wiring. Right now your description still sounds more like mixture/mechanical baseline than a failed ignition part.

My recommendation is: set hot idle, inspect the boots, then remove and clean the pilot jet with carb cleaner and compressed air. Do not force wire through the jet because enlarging it creates a new problem. After that, check valve clearance before replacing expensive parts.

For anyone following this case, this is exactly the method we use inside the free Motorcycle Mechanics Course on the platform: symptom, system, simple tests, then parts. If you are not enrolled yet, join the course for free and follow the diagnostics modules before spending money on random components.