AJS Very poor starting advice needed
Posted: Thu Aug 15, 2019 3:33 pm
I have a 500 cc single cylinder AJS overhead valve motorcycle and she is a pig to start. First a little history: she was starting reasonably well but the plug was sooting up very quickly indicating a rich mixture so much so that after a journey I had to wait until the engine cooled down so that i could clean the spark plug before returning home. Needless to say this did not fill me with confidence so i was reluctant to use the bike on runs. I could not just change the carb as it is a 289 horizontal slide type which are like hens teeth. So I had Martyn Bratby a very well respected man for his work on carburettors overhaul the carburettor. Apart from it being worn he found that someone in the past had drilled the mixing block oversize which was clearly the reason for the rich running.
I have since fitted the overhauled carburettor and got the bike to start and run and the good news is that the rich running was cured and the plug did not soot up. I now find that she is extremely difficult to start but when she does she runs well but now I am reluctant to use her in case she won't start when I wish to return home.
The bike has good compression so in my view I either have a user problem in not getting everything lined up correctly, a carburettor problem or an ignition problem.
The book recommended starting procedure is to turn on fuel, close air lever and position advance lever. Flood the carb then 3 or 4 kicks and drop the valve lever. I know I have the position of the advance and retard lever correct as I have marked the position on the lever when she has decided to start.
Most of the time when I kick her over she won't start but sometimes she kicks back like a mule and nearly throws me off the pedal. And of course now and then she will decides to start. I have tried different positions of the air lever and sometimes not flooding the carb but I can't find that elusive combination which will get her to start on a regular basis.
Information on the carb is as follows ; Type 289/148, Main jet 180, pilot 30t, slide 29/4, needle jet 106, needle position 2.
When I removed the plug after a kicking session to no avail I have found the plug tip to be wet with fuel which indicates that petrol is finding it's way to the plug. So could it be that the spark is weak under compression and only firing from time to time. I have tried different plugs of the same type and the results are the same so I don't believe it is a plug problem. Even though the carb has been overhauled I don't want to assume that it is a carburettor problem so any advice and ideas would be appreciated as I very much want to ride this bike. For information she is a pre-war model 37/8 but I am using this forum rather than the pre-war forum as I believe that there will be many more users using it. Thanks in anticipation.
I have since fitted the overhauled carburettor and got the bike to start and run and the good news is that the rich running was cured and the plug did not soot up. I now find that she is extremely difficult to start but when she does she runs well but now I am reluctant to use her in case she won't start when I wish to return home.
The bike has good compression so in my view I either have a user problem in not getting everything lined up correctly, a carburettor problem or an ignition problem.
The book recommended starting procedure is to turn on fuel, close air lever and position advance lever. Flood the carb then 3 or 4 kicks and drop the valve lever. I know I have the position of the advance and retard lever correct as I have marked the position on the lever when she has decided to start.
Most of the time when I kick her over she won't start but sometimes she kicks back like a mule and nearly throws me off the pedal. And of course now and then she will decides to start. I have tried different positions of the air lever and sometimes not flooding the carb but I can't find that elusive combination which will get her to start on a regular basis.
Information on the carb is as follows ; Type 289/148, Main jet 180, pilot 30t, slide 29/4, needle jet 106, needle position 2.
When I removed the plug after a kicking session to no avail I have found the plug tip to be wet with fuel which indicates that petrol is finding it's way to the plug. So could it be that the spark is weak under compression and only firing from time to time. I have tried different plugs of the same type and the results are the same so I don't believe it is a plug problem. Even though the carb has been overhauled I don't want to assume that it is a carburettor problem so any advice and ideas would be appreciated as I very much want to ride this bike. For information she is a pre-war model 37/8 but I am using this forum rather than the pre-war forum as I believe that there will be many more users using it. Thanks in anticipation.