i have a 1430 motor fited with 45 weber thinking of try ing different setup with twin 42mm(1.6")carbs flow 213 cfm@ 12" option 2 twin 45mm(1 3/4") flow 235 cfm option 3 single 48 mm flows 270 cfm . mini is mainly steet driven cam should rev to 7000 but mainly it's used to 5500 -6500

What size chokes are in the 45 weber now? These can be changed to suit your engine tune. For example, race minis reving to 8000 rpm traditionally use 38mm chokes (I do).

For a mild stage of street tune, 34 mm chokes would be best wherein a hotter level of street tune could use 36mm chokes. 38mm chokes are really too big IMO for the street. For your rev range, 34 mm chokes would be the go.

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Steve

at the moment 36 mm chokes .thinking about changing carbs to quieting and less fumes

For quieter running carbs then SU's would be the way to go. Choose between 2 x 1.5" HS4 SU's; 2 x HS6 1.75" SU's or 1 x HS6 or HIF44 1.75 SU 0n suitable manifold.

SU's will allow you to cut down on the fumes too, by hooking up the engine breathers direct to the carb (if there is provision, most do) or a PCV arrangement into the manifold.

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Steve

You can run a 45 Weber with a PCV valve into the manifold, I have one on my 45 Dellorto. I have a small balance tube between the 2 ports, it works just fine.

I'd say 34 chokes are too small for anything but a near stock 1275. I had them when running my 1310S motor, and they restricted the top end too much.
I've also used 38s, but found 36s are more suitable on the street.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

And one of these days I'm going to get this setup to work on my 40DHLA.... every time I try running a balance pipe between the ports the car runs like a dog. Thinking I'll try putting a restrictor in the balance pipe

Current setup, except I now pull fumes from the rocker cover, instead of oil from the drop gears on LH bends...
The PCV valve is an inline Toyota one. Balance pipe hose is 3/8 bore but the brass fittings are probably only 5/16" ID.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I ran a similar setup on mine, with a similar PCV.

But having the balance pipe fitted caused it to run terribly no matter what jetting I ran - even with only the balance pipe connected, and no PCV or brake booster attached.

As soon as you removed the balance pipe it ran fine. Go figure!

Anto,
Originally, I had the PCV valve into just one port. This meant I had to richen the idle mixture screw a turn approx on that side. But whenever I did a track day and ran to a catch tank instead ( with the PCV blocked off)I'd have to wind the mixture back in.
So, I put a balance pipe on it. Worked for me.
What idle jets and emulsion tubes are you running.... and if it's a later emissions carb, are all the idle bypass screws right in? (should be)

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I'm running .6 emulsion tubes & 50 idle jets. I played around with different idle jets and also idle jet holders, but nothing removed the problem.

I've thought about running the PCV into one runner only, but I'm a bit uncomfortable doing that in case I cause a whole lot more running problems

Ultimately I just want to sort out the breathers once and for all, but I don't want to have to change carburettors to do it!