AAAaaaaarrrghhhhhh ! Start damm you !

[titanperformance]

Sorry guys, I know you have heard it all before, but my recently acquired 93 400 will not start.
The bike had not been used for quite some time. I think the p.o sold it to me cheaply knowing it had an issue, though someone I know had heard it running a few months back, and said it ran sweetly....so I took a chance.
I charged the battery, flushed the tank and got fresh fuel, and pressed the starter. It took a great deal of spinning, but it eventually fired and ran. It was a bit unresponsive at first, but as it warmed, it ran good. That was 4 or 5 days ago. However, now it will not start at all. There are wisps of exhaust from the silencer, and a slight attempt to fire, but it justs emits the occasional backfire and refuses to start. The battery is good, and I have even jumped it from the car to spin it over quicker. It's in good physical shape, having only done 7500 miles. Connections to the rectifier are all good, no corrosion or burning. The coils and leads all look good too. The plugs are new, but like so many other posters, the spark appears weak to me. There is no obvious fault I can see, and it's such a great looking little bike, it's disappointing not to be able to use it.
Any ideas guys?

[BikerDuck]

Hi,

The problems you were having sound really similar to the ones I am having now!!! Just wondering if you got it fixed? And if so, what did you do?

Thanks,
Kat