Spada carbs

rebuilding an old spada 1000 into a T3 type thing.
The old square carbs are pretty knackered with scored slides etc.
I happen to have a pair of 36mm pumpers and was thinking about using them instead of the old 30mms
I have been told I will lose the torque and low end grunt if I use the bigger cabs.
However a fried has them on his G5 and says they work well.
Any experience/ comments??

If you retain the low comp pistons, the camshaft and the standard heavy flywheel you will retain the torque and low down grunt. I have 36mm carbs on my 950cc lump and it is a nice mix, low down grunt but a bit more acceleration when you crack the throttle open and the pumpers squirt extra fuel into the combustion chambers!

I had my heads ported and twin sparked by Rotadale in the 1980’s, with Le Mans valves fitted. I have recently fitted new low comp 950 barrels and pistons, (Baldrick rebuilt the lump) and the cam is from the original 850T that it once was. The result is great and a usable mix of sport and grunt.

I would defiantly suggest the porting work to the heads so that there is no step in the inlet port from 36mm dia to 30mm dia. The twin spark is a brilliant addition, but it would mean changing the coils as well…

thanks Chris.
No porting or twin plugging on this old tractor, keeping it simple apart from the possible addition of the 36mms…
No one else got any comments???

As noted above the only problem I can see is the step between the carb (36mm dia) and the inlet port (30mm) which may cause eddies in the inlet tract. I have read an article where a lip is desirable to the bottom of the inlet tract but I am not sure about the effect of a 3mm step all around.

There used to be a tapered inlet manifolds available 36mm at one end and
30mm at the cyl head end so that you could fit 36mm carbs straight on to T3 G5 etc

What is the exact diam of the inlet port, it may not be 30mm, maybe its 33mm like my T3, so not a huge difference, the inlets could then be tweaked to match the carbs.
Unable to say if it will be a worthwhile upgrade, put some 30mm flat top round slides on my T3 which i’m happy with but the inlet manifolds I had to buy to match the carbs had a slower bend, this made fitting an air filter a tad more difficult and resulted in pod filters and cutting the side panels to allow the pods to fit, no big deal but more work and expense than I expected.
Good luck

Found these:

Still no opinions about how a standard spada will run with 36mms though…