[spuggy]

You don't say how long ago the conversion was done, and how many miles you drove it/variety of conditions? I'm wondering if the warmup cycle was actually "perfect" before - and if ambient temps are exactly the same now?

It could be as simple that the warmup cycle (which takes time/iterations to tune, and you only get one decent shot per day) isn't quite right - either for the conditions, what you're doing now (starting but not driving), or you're simply noticing now that it needs adjustment.

In addition to checking the output of the temperature sensor(s), you may want to look at where they're located, and any tables that control the warmup cycle (usually modifies fuel trim, maybe timing too).

My M800 conversion originally used a temp sensor in the chaincase; With a lot of oil volume and a big FMOC, it was pretty futile to try to get sensible warmup with that sensor alone - it lagged head temperatures by too much - 10 minutes or more.

Fudging it with a "time-after-start" enrichment table wasn't satisfactory either. Especially on hot re-starts - with no meaningful temperature input, you'd always get excessive enrichment...

Once I fitted a 3.2-style cylinder head temperature sensor, it was pretty obvious that an air-cooled motor doesn't need enrichment once CHT is at 60C, and mine hits that a minute or so after start, even on very cold days. But if the ECU has no way to "know" that, the motor can run pig-rich until it does...