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Am I right in thinking this might be an issue with secondaries opening too early maybe? If so, why only when the motor is warmed up?

As you know a cold eng requires a richer mixture & with it being OK when cold the choke enrichment may be taking care of that then warmed up/no choke it is too lean OR if no choke is being used it might be too rich which is what is needed when cold but when warm that is too rich (not likely here) but I'd confirm the float level(s) and definitely the pump shot (tip in should be immediate/good duration). I would unhook the secondaries to take them out of the picture and find out what in hg it bogs at and did you mention what PV is in there. A slight vac leak might be a possibility but easy stuff first. Holler with any news

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