Hi Tom,
My experience with Solexes taught me that you struggle to get rid of the flat spot.
I would be a bit suspicious that you have an air leak somewhere in the inlet tract if the hole in the butterfly needs to be soldered up. Robert is obviously the 'man' when it comes to calibrating jets/choke/etc. I expect he'll be able to help.
As you'll remember I used to have a 30 MV (rather than MOV) on my car. The 'O' signifies the air bleed screw. Getting the screw bleed right helps I'm sure. The MV never ridded itself of the flat spot however hard I tried and I had to get used to feathering the throttle from idle to main. That worked after a fashion but if you ever booted the throttle it spluttered awfully and died. They really need an accelerator pump I reckon. (I messed with the idea of trying to make one).
When I fitted the supercharged engine I stuck with a Solex and fitted a 35MOH. It took me forever to work out why it didn't work properly across the range and in the end discovered that we'd lost one of the three screws holding the air inlet to the blower - so I was bleeding air into the blower through the cross-sectional area of a 1/4 BSF thread. Once plugged it worked and I got the idle right down. When it came to tuning that carb I needed Jeremy Brewster's help. Any amount of messing around myself failed to get it right - even with a Lambda sensor and a box full of jets that Charles P and I sourced on French ebay!
With the blown engine a snap throttle closure (think about approaching Sawbench at Wiscombe and hitting the brakes) kills the engine. My solution was to set the hand throttle open and not allow the main to die. I also think there is some fuel surge going on in Solexes as the problem is worse on right handed bends and the float chamber is on the left side. All of this relates to competition of course - that's when you really notice what doesn't work.
Forgive my ramblings, and see you about soon I hope..
(and for what it's worth the blown engine only worked when the original progression holes in the jet were soldered and new ones drilled lower down in the jet). I am afraid that I think that Austin 7s with Solexes may need bespoke jet refinements - at least those with blown engines..). And there are different float weights too, of course. I can't remember all the weights off by heart but you might have an unduly light float too I guess. Compromise between float weight, fuel SG and position of progression jet holes are likely behind this issue when you think about the science..
My experience with Solexes taught me that you struggle to get rid of the flat spot.
I would be a bit suspicious that you have an air leak somewhere in the inlet tract if the hole in the butterfly needs to be soldered up. Robert is obviously the 'man' when it comes to calibrating jets/choke/etc. I expect he'll be able to help.
As you'll remember I used to have a 30 MV (rather than MOV) on my car. The 'O' signifies the air bleed screw. Getting the screw bleed right helps I'm sure. The MV never ridded itself of the flat spot however hard I tried and I had to get used to feathering the throttle from idle to main. That worked after a fashion but if you ever booted the throttle it spluttered awfully and died. They really need an accelerator pump I reckon. (I messed with the idea of trying to make one).
When I fitted the supercharged engine I stuck with a Solex and fitted a 35MOH. It took me forever to work out why it didn't work properly across the range and in the end discovered that we'd lost one of the three screws holding the air inlet to the blower - so I was bleeding air into the blower through the cross-sectional area of a 1/4 BSF thread. Once plugged it worked and I got the idle right down. When it came to tuning that carb I needed Jeremy Brewster's help. Any amount of messing around myself failed to get it right - even with a Lambda sensor and a box full of jets that Charles P and I sourced on French ebay!
With the blown engine a snap throttle closure (think about approaching Sawbench at Wiscombe and hitting the brakes) kills the engine. My solution was to set the hand throttle open and not allow the main to die. I also think there is some fuel surge going on in Solexes as the problem is worse on right handed bends and the float chamber is on the left side. All of this relates to competition of course - that's when you really notice what doesn't work.
Forgive my ramblings, and see you about soon I hope..
(and for what it's worth the blown engine only worked when the original progression holes in the jet were soldered and new ones drilled lower down in the jet). I am afraid that I think that Austin 7s with Solexes may need bespoke jet refinements - at least those with blown engines..). And there are different float weights too, of course. I can't remember all the weights off by heart but you might have an unduly light float too I guess. Compromise between float weight, fuel SG and position of progression jet holes are likely behind this issue when you think about the science..