Hitchcocks Forum

Hi Bullet Whisperer ... I have a 30 mm MK2 carb for my 500 cc Bullet (KS only). I really like the improved performance with a bigger carb, but the MK2 is giving me a hard time with spit back while kick starting the bike. Your comment in the "best carb thread" on choosing Amal MK2 everytime made me want to seek some advice from you regarding timing and jetting to avoid spit back while kick starting... My bike has the tuned head from our host, free flowing exhaust and a 7,5:1 piston in an iron barrel. The carb is mounted with a velocity stack. I have had some problems with a crack in the carb body making the fuel mixture too rich and unable to control it. I believe it is sorted now, so the carb is ready for going back on the bike. Jetting is: pilot jet 25, main jet 220, needle jet 106, needle 2'nd groove from top, air vent 3,5, throttle slide 3,5. I can't remember how the timing is set. How can I stop it from kicking back most of the time while starting?... regards Jacob

Hi Jacob, that all seems pretty weak to me. I would be looking for more along the lines of 30 pilot jet, 240 main jet, 107 needle jet, with needle position set as required by testing, but start in the middle groove, air jet [vent] 2.5 and No 3 throttle cutaway. All of this would add up to a fair spend and the first thing I would buy would be the 2.5 air jet - I only recently cured a very troublesome Ducati 250 racer by changing from a 3.5 to a 2.5 air jet, it made such a radical change that this machine went from DNF's and coming last, to actually winning a race or two. The air jet has a big influence on the 'suck' through the main and needle jets and is cheap and easy to change, so try this first. Regards, Paul.

Hi Paul - I've never understood the way this air jet functions in the Mk2s - can you throw some light on how it works as it seems a crucial matter to get it right between the two sizes AMAL offer. Thanks.

Hi Paul... thanks for reply. I'm fortunate to have almost all the suggested jets from my experiments on jetting the carb right. Before I became aware of the crack in the carb house I was trying so many different jet combinations. Along that way I found out that the needle was a methanol needle, so a correct needle and a bunch of jets was purchased some time ago. Only a 240 main jet is missing, so I will start with a 230 main, 30 pilot, 107 needle jet, 3 throttle slide and a 2,5 air vent. In which of the possible two locations for the pilot jet do you place the jet? Do you use the cold start plunger on when kick starting a cold/warm engine? Which jet do you recommend for the cold start circuit? Do you have any advice on a kick starting technic for a cold engine?... I have meassured the petrol flow to 1 liter in 2 minutes. I believe this should be enough petrol flowing to prevent fuel starvation. I run 95 octane petrol of all brands... regards Jacob

Here is some very useful info, explaining just about everything about the MK II's, although the spec tables state 3.5 as standard for the air jet on 4 strokes and it took the fitment of a 2.5 to fix the Ducati mentioned above. In the Hitchcocks catalogue, page 274, the air jet is shown as 13a in the diagram and listed as 2.5 [std] or 3.5. In the section about pilot jets in the info in the link, it tells of the different locations for different applications, although in a 38mm MK II I fitted to a Fury, I used two pilot jets, one in each location and this also worked well in this instance. Here's the link:
http://www.britcycle.com/Manuals/AmalMK11Tuning1.pdf

Hi Paul ... good reading to understand how the carb is working... I have done some initial testing with the new jet set up. Fairly easy to start, but a devil to keep alive, unless I have the throttle slightly open. I have had to re-install the 3,5 air vent to start the bike. When keeping a steady (but too fast idle) I can use the cold start plunger (jet 40). When it is turned off, the engine dies out unless I give throttle. So for starters my concern is to keep the engine alive at idle... Jacob

It's good to know that someone on here knows about MK2s. I've got one on my Armstrong and it's been an utter pig to get it running correctly, I think I've cracked it now but more to luck than judgement. I have a spare that I bought before getting mine sorted, I assume that by re-jetting it I can stick it on my old 350 ?

Hi.. just as things was looking a little bit right, starting ended up being impossible. When checking on timing I found out the the bob weights was blocking in a too advanced position for starting. Then I sorted this little thing. Next would be to do some testing on the jetting. Then the repair of the crack gave up. And by now I have almost given up. The Mikcarb VM28 is back on the bike, and I'm contemplatimg on buying a Mikuni TM32. Anyway thanks for input and help... regards Jacob

Sympathise JTL,

Somedays your the bird.

Somedays your the statue..

Thanks Gwilly