There are my suggestions in the 750 f.a.q. about this...

Oops - developed some problems starting. Once riding for a while it has conked out at the lights and this time in the morning it was not starting. When day warmed up I got it going - just - then next try some backfires. Must be an effect of my carb work. Initially it started fine. Any ideas?

Thanks for suggestions offered below - the issue I found was the spark plugs were too black and so not much spark. I changed them and also took out the Accelerator pump jet 60 that I put in and returned that to the original 40. Yes - started first time :-)

Could have been caused by one other mistake I made *

I got this small tank sorted out so I could test it running, which is why when new spark plugs fired I thought, while I'm at it, I'd better change back the pump jet form my 60 to the original 40 - my guess is that I made it too rich especially at low rpm, since this problem arose while riding too and from work (some motorway but also around town riding). I know my little tank is a bit small for riding, but it is far better to have this than taking the big tank on and off. I also need this to balance the carb iddling addling using a water manometer as explained by higgy and Nicola (ducapaso) in this thread and elsewhere.
While I was at it I used some Carb cleaner as i worked inside and out.

From this view changing the pump jet was easy. Just undid four screws on top, gently lifting off top part to expose jets. Then unscrewed tyher pump jet and replaced it. * I had hda a niggling feeling about a washer left over from the last job abd sure enough the pump jet only had one washer under it (there should be one above and below, So I made sure it was put back correctly this time - actually might have been the reason just as much as the pump jet size - I am not sure.

I feel my learning curve is improving. I knew nothing about carbs a month ago. now I am confidently changing a jet

I'm interested to know what model honda you got your coils off.

I would check all the connections associated with the relay mod first maybe there is a loose connection somewhere.If that doesn't fix the problem then you could try the original coils again,to see if one of your new/secondhand coils is faulty.You mentioned that you had to change the leads,thats another thing to check.I'm planning to do the relay mod this weekend the only thing I haven't got is the coils.I,m not a big fan of using second hand parts.The local auto shop has Bosch GT40T coils for $58,I need to double check the ohms,but all the info I've got says that they will be fine.I,m a noob when it comes to the weber so I can't help there.
Cheers Ken

you might have a look to wiring upgrade in 750 f.a.q.

3 ohms to 5 ohms is the range you need

I have the 3 ohm dynas and wire set I got from BevelHeaven,works very well. Have not had plug issues in about 2500 miles now. He also has the brackets which makes it a bolt on job with the exception of the wire terminal ends which you can get at any electronics or auto supply.
on polishing your intake,the most important detail is to smooth the differences between carb,intake.gaskets and port sizes,remove the least amount of metal you need to smooth the transitions

The top of this thread has been updated .
For all those running the Weber, and for those that swapped it out this is a great read
Great work Romus..................

Finally an explaination for the technically challenged