T3 VHB30 carb jetting issue on bellmouths

My otherwise standard T3 has been fitted with open bellmouth inlets instead of the standard filter system. Previously jetted to 130s by its previous owner, I’ve gradually jetted them up to 145s to try and cure a last 1/4 throttle flat spot (irrespective of revs) - but can’t seem to get rid of it. Otherwise it carburates really nicely. One test I did was to invoke the flat spot (full throttle), and pull a tiny bit of choke to see if it responds to a richer mixture. It did, and picked up nicely. So this would suggest the main jets are still too small at 145. Question is: has anyone on the forum been through this process, and if so where did they end up jetting wise?
Carb needles are on the standard middle notch.


Suggest checking float chamber level. If good then raise needle a notch.

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I checked the floats, and they’re spot on. I’ll try raising the needles, but it’ll probably make the midrange too rich. I read an article on Dellorto carbs which suggested the last 1/4 turn to full throttle is main jet only. I’m tempted to stick 150s in there to see how it goes, but would rather avoid the expense if the flat spot issue is caused by something else. Watch this space.

I’m running an SP1000 with VHB carbs, fitted with bell mouths and 150 main jets.

I’m still watching this space!