Starter kickback when warm

[WideOpenVTwin]

90% of the time, when I crank the motor when warm (engine off for less than ~30 minutes), the starter immediately "stops" as if the engine kicked back. If I release the switch and try cranking again, it starts just fine. This never happens on a cold start. This has been a problem for several years.

Possibly related, the engine sometimes runs rough during takeoff for about 5-10 seconds, as if it were flooded. This is a more recent problem.

Things I've checked:
1. I replaced the starter last season due to a flaky solenoid. This problem persisted.
2. I've checked several times for water intrusion. The cylinders are dry.
3. I've changed the riser gaskets. No signs of water intrusion before or after this change.
4. Battery, cables, connections are all in excellent condition.

The only things left I can think of are timing or excessive fuel leaking into the cylinders. Has anyone experienced these symptoms or know what to check for?
This is my next course of action:
1. Check timing (Waiting on initial timing pigtail. These distributors use an electronic advance, right? )
2. Check float level

Thanks for any ideas you can provide.

 

[WideOpenVTwin]

I realized this motor has the BID distributor, so no need to set it in base timing mode.
I checked the timing, 8* on the money (assuming the balancer hasn't slipped).
Does this distributor use centrifugal advance? If so, I wonder if the weights are sticking and leaving the timing in a more advanced state.
Has anyone experienced this?

Thanks