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I have been recommissioning the bike over the summer after not been used for 15 years, I thought I had it sorted after changing the in tank fuel pipes, but now i have a problem starting it sometimes you can crank the starter for ages with no sign of life and yet other times it kicks straight up, the fuel pump is priming and feed pipe is under pressure, I have had the plugs out and the coils are sparking and the plugs look wet, there are two things that I suspect firstly when I fitted the new fuel fillter it fitted the other way round to the one that was fitted before but the arrows were pointing in the right flow direction on the old they were pointing opposite although it was the same model of filter, secondly cant be sure but I think I seem to have the problem after killing the engine with the right handlebar mounted kill switch and not the key I am not to up on the electrics but I think it points at this, any help please many thanks Alistair

Might have sorted it, I have been keeping it at work, the building is always 19 degrees c and I have been trying to start the bike full choke so I think it has been fouling the plugs, they look very sooty so getting some new plugs in the morning, I think linking the start problem to the work I did in the tank may not be correct and was just coinsidence fingers crossed, I will see how it performs with new plugs and let you know, who knows might even get to ride it, cheers all

if the bike has been unused for so long, and you haven't done so already, my advice would be to clean the injectors.

The "choke" isn't a choke, it's a fast idle lever that simply opens the throttle off the stop a little to keep the engine from stalling when the engine is cold. Invariably "full choke" opens the throttle too much to allow starting. When I first got my ST4s I had difficulty starting it the first few times until I worked out what was going on.
Try starting the bike with the "choke" off, opening it a little at a time while the engine cranks until it catches. If this is your problem you will find that it fires up after you have opened the "choke" by a small amount. Once you have worked out how much it needs you can use this setting for every cold start and it should fire up right away. My 907 needs about 1/4" of "choke" for a guaranteed instant cold start.

Thanks for all the advice, what would be the best method of cleaning the injectors, many thanks all re Alistair

Hi Alistair,
I posted that advice because I know that fouled or sticking injectors is a problem on older cars which experience starting problems. Difficulty starting from cold can be a problem with restricted flow, and difficult starting from warm can indicate a problem with the injectors failing to close properly and allowing fuel to dribble through them.
This might not be the source of your problem, but if you want to get them cleaned properly, then find a company that uses an ANSU cleaning method. This not only cleans the injectors and equalises the flow rate, but allows for the spray pattern to be checked.
By the way, I too have an ST4s, and if I open the fast idle lever to its full extent before starting, all that happens is that the engine revs are way to high for comfort. I see the whole point of warming up the engine is to allow oil to get to all critical areas and reach the temperature that allows correct lubricational viscosity whilst causing minimal wear.
By the way, have you tried starting it without using the 'choke' lever and keeping the revs up on the throttle?
And if your plugs are sooty, what is the condition of the air filter?
Kindest regards,
Kevin

My ST4s, ST2, and 907 won't start using that lever, but its nice to hold the idle high while it warms up.

Cheers, Phil