Surge in Power at 5K rpm plus

I didn't think this to be normal, but the old girl will get upto around 5k with not too much fuss (it's still going through it's "italian tune up" -all clean now), then all of a sudden it's like a turbo kicking in (i have checked there isn't a sneaky one lurking anywhere ;) ), so am a little confused as to why at such high rpm a big old lump will of a sudden decide to enjoy life that much more?? Air filters are clean, Carb could probably do with fixing/changing/cleaning (not really touched it to be honest), Dis cap, HT's and sparks look OK (again could do with changing though) Any ideas - would prefer that sort of kick further down the rev range! cheers,

I'm wondering if you actually have the original camshaft fitted. Your power symptoms sound a little like those with a higher lift, bigger overlap cam, lumpy at lower speeds, then suddenly everything chimes in. I had, years ago, a very second hand Mini, cheap temporary transport, which ran and sounded like a bag of nails, coughing at lower speeds, until one day, overtaking something on the A1, I exceeded my self imposed (cos it had about 75,000 miles on it!) rev limit of 5000rpm, and it took off, engine went all smooth and quiet as well. In its dim and distant past, someone had fitted an almost 'full race' cam. I had lots of fun with it after then, scrreaming up to well over 7000 rpm!

My gues is its a fuel mixture issue. If the needle has worn and been moved to compensate and get it through MOT it will have also affected higher rpm. Changing the needle would bring it back to original spec but whilst you might gain at lower revs there is a risk you might lose out at the top end. Really you would need to check misture right through the rev range to see what is going on. Mike

Is the motor a B230K? If so, it should have the Solex Cisac twin-barrell carb. The second stage should open around 3000 RPM, and you do feel a boost when it does. The second stage is operated by vacuum; a rather vulnerable system compared to the all-mechanical Webers. In your case, perhaps a small vacuum leak causes the second port to open at higher RPMs? Or a sticking throttle shaft or linkage?