Hitchcocks Forum

..A lot, a lot of German bulleteers have equipped their bullets with a 30mm pwk clone, jetting about 125 main and 48 idle..
as the amal on mine is eh, not very well i wanted to copy this an bought an upper-price level polini pwk and equipped it with these jet sizes..
But the engine chokes on it, without air filter! Far too rich..

I do not understand.. really..
even much smaller jets don't seem to make big difference..

Are there here folks running this kind of carb?

Greetings from rainy Holland.
Arnaud.

Your idle jet is a bit bigger than normal but thats only at idle and 1/4 throttle. You need to lower the needle jet and see if that helps. Jetting an unkown carburettor is not easy.

Hopefully you’ve bought a four stroke version and not one for a two stroke.

Brill Bike Parts sell Keihinoid PWKs in the UK under the JRC name.

http://www.brillbikeparts.co.uk/index.html

They've helpfully provided a tuning guide for various British bikes, maybe their recommendations for the BSA B50 (same bore and stroke as the 500 Bullet) would be pretty close, at least as a starting point.

http://www.brillbikeparts.co.uk/images/jets.gif

It does seem to me that there is some sort of a downer on the mikcarbs, which as far as I can see, work perfectly well and can be serviced (or replaced) for sweetie money.

The amals are fine when on wide open throttle but they are a glitchy pain in the backside at lower throttle openings. The more worn they get, the worse they are. The choke is a total pain in the backside too.

SW, I posted the very long saga of my faulty Mikcarb. The trouble was poor quality control. The replacement Wassell Concentric has been faultless and the bike pulls far better.

I found that the engine started first kick and ran perfectly without using the choke at all, the tickler is sufficient, so I removed it entirely and blanked the aperture for the cable.

I have read the anecdotal evidence that the slides on the AMAL versions can wear quickly and the pilot bush can get blocked. I fitted an oiled foam type air filter and a good quality fuel filter and so far (the bike must have done about 7,000 miles since I fitted it) it has not shown any signs of wear or other trouble.

I've got an amal Mk1 concentric with a worn out slide and equally worn body sat right next to me.

Which type of air filter did you use?

Maybe the Wassell is better quality than the original AMAL.

The selling pitch for these carbs [JRC/PWK] is that they will help solve the ‘problem’ of modern petrol. This is so much nonsense. Any carb set up correctly will ‘solve’ this ‘problem’. It doesn’t require a particular type or make of carb.

I’m with SW in saying that the Mikcarb is perfectly OK when set correctly and kept clean. But I’d still claim that the AMAL Concentric is as good as any of these carbs – especially the Premier version which has addressed some of the main weaknesses of the older versions: wear between body and slide and the pilot bush problems with an easily removable pilot jet.