Having finished a complete rebuild of my 1971 A65FS, I have a running issue.
If I tickle the carbs (twin carbs), the bike will fire up after about 3 kicks and run for about 2 seconds and then die. Feels like it's run out of fuel. If I tickle the carbs again, I get the same result, runs for a few seconds and dies. It won't start without a tickle.
I have new trispark electronic ignition and I am happy that it is static timing is correct and there is a strong blue spark.
I've checked that all jets are clear and that the float chamber is filling and the float needles are working okay.
Clean fuel is being supplied by remote tank, so no contamination issues.
My carbs do not have the air valve (choke slides) fitted for some reason. Could this be the cause of my problem. Any ideas or previous experience appreciated.
Lack of air slides could be a problem. If you can get to the intakes try putting your hand over one and see if it picks up.
Are the carbs Concentrics? If so I would suspect the idle jets. I had a very similar problem on my Road Rocket with a concentric. The passageway behind the idle jet was blocked solid despite a lot of cleaning. Its very hard to get to. I ended up drilling it out so I could get a wire though then fitting a removable jet from the Mk2.
It is odd as you have twin carbs but modern fuels seem to cause rock hard deposits in carbs.
Of course 90% of carb problems are ignition and visa-versa so you could still have a lose wire or bad connection!
Try screwing both idle screws fully in then back out about 1 turn.
Carbs are standard Amal 930 concentrics. I'll have another look at the idle jets, but all seems clear and I can blow air through with the pilot air screw removed. The bike was stood for over 20 years before I got it. I'll also try manually chocking it with the intakes removed.
Thanks
My carb is a 930. There are two passageways into the idle screw hole. This fooled me as the air passage way will be clear as its bigger. But the one you need to clear is through the tiny brass jet and back to the hole in the bottom face of the carb. Its damn near impossible. Drilling the jet is not a disaster as you can tap the other end of the passageway and fit a removable jet, this is a decent fix. But despite the claim that the jet size (25) matters I reckon that the fuel only just flows and no jet would still work.
Look at the pic on Page 5, the blue bit will be fine but the red bit is probably blocked.
You can drill that tiny jet to say 1mm and try and get a fine wire through. It may work. If you drill bigger (I did) then you screw the new jet into the hole marked "pilot hole drilling" and it works the same.
https://accessories.hitchcocksmotorcycles.com/core/media/media.nl?id=188680&c=1062795&h=5bbcad5e8e17f80befa4&_xt=.pdf
i did a top end rebuild on my '69 FS last year and had a problem with starting/running. Carbs were Mk1 concentrics with choke slides fitted. L/H carb idle speed could not be altered despite removing the carb for cleaning,float position etc. Had to source another from eBay. Swapped jets, set float height and cleaned idle passages and bike started ist kick, but i do need to use about half choke and flood the carbs to start. Engine needs to get quite hot before choke fully off.
There are two small holes before and after the down stream side of the slide in the floor of the carb. The up stream hole is 0.036" (#64 drill) and the down stream hole is 0.026" (#71 drill). These need to be clear for the pilot circuit to work.
Carbs without choke slides usually have the idle set too rich to compensate.
My Lightning needs tickling and the air slides in this weather, in Summer it just needs tickling. 930 concentrics.