1951 G9 carburettor grief

[ChrisD200]

Hi guys, I’ve had a 6-month sabbatical from my 1951 G9 Matchy whilst I agonised over my failing Bullet – neither worked and I thought I’d fix the easier (Bullet's still not right!). Last time I wrote (1st June) the Matchy would only run with the air lever full on. It had never done that before and I couldn’t understand it. Advice from here was the logic of “the cylinder leaked air through the valves or the carb did or a bowed carb flange or low fuel level. Since both cylinders gave 120psi, I assumed the carb was the problem. Cleaned carb (1” Amal 76/1AG) in ultra-sonic bath, polished all innards and outside. Looks better but won’t run better! So I assumed the parts had started to fail and I bought £65 worth of correct needle, needle jet, main jet, throttle valve (slide), float+needle. Put them all in and tried it but No better!! Tried new plugs (standard NGK B6ES). Surprise surprise, its much better, but still won’t run properly. Revs OK but now when I let the throttle go and the slide closes (yes, it closed fine as seen clearly with mirror) the revs stayed really high. Open-close throttle several times and the revs would finally drop. Spent much time polishing the bore of the carb just in case I was going blind so the slide valve could moved most easily. Still didn’t fix the problem. So testing one-by-one I replaced all the brand new correct size Amal parts with the old worn parts. Even when all the old parts had been replaced, but for the needle and needle jet, the revs still seemed to get stuck. Only when I had finally replaced all but the old needle would the bike run and the revs come down OK. So the old needle+jet combination cannot be easily replaced as the correct ones don't work right.....I wonder what they are (no markings)?
In the final analysis, the original problem was a failed plug! But what will happen when these worn old carb parts really wear out ? Still it all seems OK so it should make the long road trip of 700kms each way in February…..!
The moral of this expensive and time-wasting tale is this. Test spark (magneto is good, frecently rebuilt and both sides have ¼ inch spark) and change plugs first! What did the plugs look like? Well both (B6ES) were sooty (because I’d run it with choke largely on), but one had a patch of light tan where the centre and side electrodes are closest so maybe that plug was OK.
Anyway I suspect the plugs could safely use the next grade up of heat and maybe an iridium would be of value in the coming years like an NGK BR7EIX – anyone got any thoughts on that upgrade?
Well, cheers all.
Chris (from Cape Town)

[Groily]

At least with the plug change you figured out the initial problem.
Having got sick to death of an incorrect Monobloc on my slightly later twin, I got a correct recon'd Type 76, correctly supplied with all the correct bits by Surrey Cycles in the UK. No problem since. Might be worth asking them to confirm what they think's 'correct' and supply a spare needle for next time if they've got one. (Unless that's where the latest one came from! Does it look different from the old one you've put back by the way?).
On plugs, I've been happy enough with Champion N4s, and B6/7ES over the years (occasional duff ones), and it's currently on B7ES. Frankly I can't tell the difference, it always seems to start first go and run fine.

[crawsue]

Could all be in the head,but my G80 seems to be a better starter on a NGK Iridium (6 something....too cold to go out to the garage to check!..-6c)For a fiver a pop on Ebay it was a no-brain try a couple of years ago.As for dud monoblocs,there are plenty of stories on this forum of people getting to the end of their tether and eventually buying a new carb,and problem solved.Have a pal with a Norton International,drove fine but would never tick-over reliably,eventually bought a new carb.....ticks over like a sowing machine.

[Groily]

Ah, but then you have a serious amount of mixture to encourage into life there crawsue. We folk with puny doubled-up eggcups for cylinders don't have to climb the same mountain!
Tis all in the head though . . . you're right enough there.

[ChrisD200]

The penny has dropped, I couldn't get a fine bristle through the tiny holes leading to, from and through the idle jet cavity and the jet block. When I blasted that with my trusty carb cleaner and wiggled the bristle, it suddenly cleared. The bike now idles OK...Typically though the taps have now started leaking (I think it is deliberately planned not to ever work properly). Chris