Oh yes, the myth of bultaco fragility.
Hi Expat, I concur w Mark on this. In my view its on a par w Maico-breako, usually perpetrated by people who had little/nothing to do w them, weren't up to doing basic maintenance or perhaps got a lemon (didn't every make have a few of those?)
Much of it stems from the 60's, but wasn't every competitive bike fragile then? Remember the british stuff! Materials & quality controls weren't nearly as good then as even the 70's stuff.
Occasionally they did have a 'bad' model, eg the 1st Astro which apparently had too-little bigend clearance & seized frequently, but is easily fixed.
My bro & I had several bultacos (& a couple of maicos, among others) & they were always stone-reliable & 2nd/3rd-kick starters w just basic regular maintenance. Ours all had standard carbs & electrics too. We couldn't afford anything else. I still have my 1st one (M63 71 SherpaS) & the only new one I ever had (76 M167 pursang)
The early ones needed some jetting refinements & I'm told eletrics could be suspect (but ours never were). Brakes weren't great then but thats easily fixed w modern linings. 360 engines can be improved w roller LHS main bearing on crank like later 370s had. Keep an eye on primary chains. Gear selection can be improved w a mod to the drum.
Many found the (early) RHS shifting & LHS kickstarting awkward. If you rotate the kickstart lever forwards on the spline & kick backwards w the right leg while standing next to the bike, its easy enough to get used to & they start readily, but there is a bit of a 'technique' to it. And gearchanging requires more lever-throw than a jap bike but that's not hard to get used to either.
Of course somebody will bag them on account of one bad experience, but you'll find such people w every make. They had all the important stuff for a competitive bike - handling, power, plush suspension, lightweight etc. I still have not ridden a 70s 250 that explodes out of corners like a well setup 'pomeroy pursang' M120/135. Others 250s made more power but none made better power that, combined w the flyweight, hooked up & exploded out of corners like a scalded cat.
They were/are simple but very effective - much more than the some of the parts. Theres a certain synergy to them that gives them a charisma which many find addictive for a 70's bike.
Talk w Don Newell (Bris) & Peter Schoene (Melb) about setup 'secrets' & I doubt you'll be disappointed if you own one.