Don't know nuthin about GR's cams, but lots of people like them. I ran a 1380 with an STR930 (basically a Piper 649 copy and the required cam for Mini Miglia in UK), for 20 years, and with careful attention to jetting the 45 weber and timing, could cruise in top at 2500 on a 3.4 diff - would pull from 1500 with foot to the floor in 1st and second. The key is the idle/off idle/low speed transition - needs to be a bit lean, then a bit rich to avoid the hole, then leaning out a little into to main circuit. Suggest you beg/borrow a heap of jets and aircorrectors, buy a Sutton pin vice set (basically a pen that holds teeny weeny drill bits) and get a little soldering kit - then you only have to spend a few weekends changing out/drilling/soldering/changing in about 50 squillion combinations of tiny fiddly $*!@@@ little brass pieces to get it somewhere close to right - but when you do.....lordy lordy!
(or take it to a rolling dyno that knows minis)
Common mistake is using chokes (main venturi) that are too big - i started on 36s, bought 40s cos' bigger has gotta be better, right? Wrong - air speed drops and signal strength in the aux venturis is weak. Fine over 6000, but if you live in the real world, performance and torque between 2000 and 6000 gets the job done. Came back to 38s. Also tried bigger auxiliaries and pump jets - same dumb theory, same disappointing result. Tried idles from 40-65, mains from 145 to 215 (yeah, there was a manifold leak), correctors from 140 -210.
Wound up with Main Vent (38), Aux vent (3.5) Pump bleed 50, long stroke pump rod, idles 60F9, one 0.5 hole in each throttle plate for better idle/signal strength (new webers have an additional adjustable airbleed and 4 transition holes), main jets 185, correctors 210 and 60 pump jets. A proper in cab air/fuel meter is a revelation, and even good rolling road guys can't quite replicate actual driving conditions, eg sitting in a traffic jam for 20 mins.
My advice - start with mains at 150, correctors at 170, venturi as above, and put time and effort into timing the cam properly - get the rocker clearance right, the plug heat (ngk bp6es) and gap right FOR YOUR MOTOR! Every engine is different. there is no guaranteed formula - patience, perserverance, and pizza will get you there eventually. Work it slowly richer. Or start too rich and work down - keep notes. Don't sustain high revs until you 'feel' the engine wants to. Watch the temperature - steady increase and overheating/pinging often means timing retarded/mixture too lean/plugs too hot, low engine temp and 'doughy' engine/blue smoke can mean too rich/timing too advanced. Red and blue lights in your mirrors probably mean you've got it right and wrong at the same time.... Stick with it - its easy to bolt on bits, but chances are you have created your own unique little combination, and it's gonna take time to figure out what it needs. Bon chance!
_________________ Min - 1970 MkII S, 119hp Dave Anton 1380, SH Engineering belt drive, 1.5 rollers, 123Tune ignition, 48 DCO SP Weber, HP Headers, MSD, Maniflow ex. Swiftune SC/CR 3.7 + ATB, all KAD front, antiroll bars and gas shocks, 6 inch Minilites with Dunlop Sports
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