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[Chris Tindal]

Today I took the 59 BH Bullet up to Skipton with the wife on pillion. The bike went well, cruising at 60 and even hitting 70 on Skipton bypass. One the way home it started popping a lot on the overrun. Once home I discovered the top of the Amal 389 had almost unscrewed, so assumed it must be letting air in. All I did was screw it back down tight, but after that the bike kicks back viciously every time I try and start it. It will kick back even half way down the stroke and there's no way it will start. I took the carb off, checked the cables and slides, drained the float bowl,and check the float wasn't stuck, but all seems well, nothing's been changed only me screwing down the top!!

I thought kickback was due to the ignition timing being too advanced. It's fitted with a Thorspark 12v electronic ignition inside the old SR1 that has been brilliant so far. Normally it starts first kick hot or cold, sometimes even by just gently turning the kickstart. Thinking that the ignition timing may have coincidentally slipped, I re set it a couple of times to be sure it wasn't advanced but it's still doing it. What could have suddenly changed? Is the carb a red herring? Is there any other reason for kickback other than advanced timing? I'm baffled at the moment.

[Jamesy]

I've read on other sites of people getting kickback due to poor voltage roundabout the electronic ignition ie. poor connection,battery.I also read one guy saying he had it because of a weak fuel problem.

[Mark M]

My suggestion is same as Jamesy, weak mixture? If the carb top came off vibration must have been quite strong, could the manifold nuts have loosened off allowing air to enter at the flange?

REgards, Mark

[Mark M]

And if the engine was still hot that would make the problem more pronounced....

REgards, Mark

[Aethelric]

If it kicks back when the engine is cold it can't be pre-ignition. I can't see how a carb problem would cause kickback. I would think all that could cause it is a spark coming too early.

[Alan R]

Hi guys-----Just some random thoughts for consideration}------A) as the carb top was unscrewing did you not feel a difference in the throttle cable clearance ??.........
B)"Cause and effect" reasoning would suggest that once you tightened the top back down again the symptom should have ceased ??.....(or conversely if you undo the top again it should cease ??)......
C) Also popping and banging in the exhaust on the over-run is generally due to a poorly fitting exhaust system, normally where the pipe exits the head.....
D) Yes, those modern Electronic systems can sometimes need a fully charged battery to "pull" the starting spark timing back towards TDC.......Last year my good mate Fred had exactly the same symptoms on his 1950's Bullet....I tried as well as himself ( Now in his 80's ) to kick start and had exactly as you describe.....We re-fitted the O/E points and all is well again..

[Chris Tindal]

Thanks for the replies everyone. Tonight I re set the timing and it still did it, so I took the carb off, cleaned it and reassembled everything ensuring it was tight to the head and the top was tightly down. The throttle and air lever cables were checked are just as they've always been. Tried it again and it's just the same, can't even get to the bottom of a stroke before it boots back hard. The battery seems to have plenty of charge as the lights and horn work, but I'll put it on charge and see if that helps.

[vince]

Hi, is the auto/advance sticking? Vince

[Rattlebattle]

To me it has all the symptoms of the ignition timing being over advanced. If it’s firing half way down the stroke I don’t see how it can be carburation unless it’s chronically flooded. The plug will tell you this. If you have reset the timing accurately then it must be the electronic ignition unit failing. I would suggest the carb top coming loose is caused by vibration, maybe what has caused the ignition module to cry enough?

[Rattlebattle]

PS If it still has points then maybe it’s the A/R as has been suggested. Either way I’d take the plug out, earth it and gently kick on the K/S to see if there is a rogue spark when there shouldn’t be.