Starts fine, misfire cold, then fine - ideas?

[bherlingo]

With regards to the timing you have a point but again can be temp / speed dependent in the rev range. I don't think the bingo is complicated enough but some engines have a thermo element to control advance / retard for emissions. I wouldn't expect it to be overfuelling otherwise it would be white smoke and you'd smell neat fuel. Are you using the injectors from your old engine?

No, the injectors are from the new engine and are unproven. The new engine allegedly had done 51k - but I have no proof of that. Again I wonder if the injectors could have that effect for just 3 minutes and work perfect on tickover and then on normal running - it would need to be all of them too. The key is the temp difference, if you turn the engine off you have to leave it to cool completely before it would do this again.

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I just did a little experiment and here's what happens - I went out and started it, problem there. I went to the front grille whilst it was ticking over and waited for the 3 or so minutes with my head by the grille. There was a definite note change in the airbox area at the 3 or so minutes and I tried the engine and it ran perfect again. Is this normal (the noise change not the resultant problem of course)
What is it that makes the change, its definitely not the engine tone