I was a bit 'ooo-er' when I investigated recent lousy tickover on the A yesterday, and found that the throttle valve in the 389 I bought new not all that long ago (well, maybe 20K miles or so) was well and truly fubarred. I'd initially thought it was typical pilot circuit trouble due to resiny sticky fuel etc etc, but doing all the usual there hadn't done the trick.
Stuffing a small gizmo in the orifice to stop the slide chattering without blocking the airflow restored tickover, and made things sound a lot less clacky.
So, I thought, as you do - 'How bad is the Bore?'. To which end, I thought it would be mildly useful to know what the makers' dimensions are for the 'ole. Hence a quick call to Burlen.
I didn't come away much wiser.
Bloke said "1.4 inches' to start with.
Exactly that, sayeth I?
"Er, no actually, 1.44" cometh the response.
Right, yeah, maybe?
While I was on the dog, thought I'd just check whether another new carb, with 3.5 valve and anodised like wot they sell now, was available. That was too complicated . . .
Like it says on their website, std 389s come with 3 slide 300 main jet, etc etc, and for anything else 'Ask'. Which was why I was, er, asking. But they 'would have to come back to me on that'. Why? If they have the slides - they do cos I've ordered one online - and if they have the bodies in inch 'n 'n 1/8th - they do although I haven't ordered one online . . . I was a bit perplexed, being of a simple sort.
I think I actually bought the worn carb from Alan Hitchcock, in fact, who was able to provide the required innards after a quick phone call and get it shipped to me in France in 3 days. That's the Hitchcock Gold Standard.
Anyway, just for now I've ordered an anodised 3.5 valve, new needle, and also, ahem, a small air filter (online from Burlen) . . . Never had an air filter before, so that could be fun. Doubt it'll go on in a hurry or even at all, but we'll see, and maybe have to knock up an adaptor, and then play with the jets . . . oh the joy. And when the valve's bore DOES turn out to be as bad as it probably has a right to be, I'll be back to talking to Alan H I suspect.
Funny thing is, another 389 I bought new about the same time (2013) isn't half as worn out, also with a simple zinc slide. In fact no other carb of the 7 in constant use (5 being Monoblocs) is worn, or not worn enough to affect running.
So I guess the A must have had sand kicked in its face by some wannabe Charles Atlas among its 'mine bigger than yours' companions in the shed. That would be typical brotherly behaviour of course, towards a bike that is vomit-makingly dependable from their point of view probably.
