Posted by Wayne on 7/17/2009, 9:35 pm
86.171.43.90
Have finally got my Bonnie back in one piece, but having real problems with starting & low speed running.
Have today removed, cleaned & rebuilt the carbs on the Bonnie. Had hoped that I'd find blocked primary jets but they were as clean as a whistle. Checked that the carbs were clean, with no blockages anywhere, including the cold start jets.
Replaced the o-rings on the tickover screws & mixture screws as all four of them were a bit aged. Reset everything to factory settings. Checked that the chokes were seating properly, and they are.
Replaced the carbs on the bike.
Tried my old starting technique - full choke, kick through a couple of times with ignition off, turn ignition on, big kick. Not a whimper, not even a chuff.
Turned the choke off - bike fired every kick and then managed to get it started after about 20 kicks. Ran very crisply, revved well, even managed to get it to run at tickover speed for a minute or so. Then it cut out. Tried to start it again, which involved about another twenty kicks or so again, with it firing every kick, kicking back a couple of times, then starting & running well again. Stopped the engine - took ages to start again.
Now, the only things that are different about the carbs since I last had the bike running well is that I've replaced the floats & needle valves, which has stopped the flooding problem, and I've put bigger main jets in, as I'm running shorter less restrictive exhaust pipes. I went from 200 to 210 main jets, which was what was suggested when I bought the exhaust pipes.
Due to the fact that the bike doesn't want any choke, & it ALWAYS needed choke to start before, I'm guessing that I'm getting too much fuel going in now, which is causing the starting problem? Could this be the bigger main jets causing this? I had discounted that as being the problem before, as I didn't think the main jets would come into play when starting the engine, but thinking about it, I suppose that as the needle gets lifted as soon as I twist the throttle a little (or possibly as the slides are slightly raised anyway on the throttle stop screws,) maybe I'm getting too much fuel through the main jets straight away?
Any Mk 2 Amal Concentric experts in the house? DO the main jets have any bearing on starting as I'm now starting to think?
Or does anyone think I'm barking up the wrong tree, and that I need to be looking elsewhere, eg ignition? (have checked by the way, and I'm getting a lovely big fat spark on both plugs.)
Need to get this sorted asap - the bike is ready for his MOT now, just need to get him running well enough to get there.
Cheers
Wayne
12
Message Thread:
« Back to thread