Tach drop out and not running right

I bought this bike in December, it looks great, runs great and everything works. Except yesterday I started it with the choke on and after a few seconds the tach dropped to zero. While riding I noticed that it wasn't running right as if not all cylinders were firing or the fuel was bad. Once in a while the tach came on and the bike ran good. I stopped, added fuel and started it up. All seemed fine until a few yards and the same thing happened. I took it to a dealer.............who is having a field day with it. I've been riding this bike 60 or so miles a day without any problems. Any thoughts?

You didn't say what bike. Assuming 1st gen since 2nds don't have a factory tach. The tach fires off the #2 coil, start testing there.

Also check to see if running on 2 or 3 cylinders. Mine dropped 2 with a bad tci. They run amazingly well on 3.

Yup! Your tach receives its signal from the primary side of the number 2 coil. Chances are it is not the coil but the firing signal coming from the TCI. There is a lot that can be done and a few things that can cause this. There are diodes in the TCI that are known to fail. There is always the possibility water or condensation has gotten inside the plastic box which can be dried out by removing the cover and baking in an oven at around 250 degrees F for an hour or so. Put a bead of grease or Vaseline around the cover when reinstalling to help waterproof it, and relocate the TCI on top of the airbox to further protect it!

We need to know what year your Venture is as on the earlier ones there are 2 pickup coils that one of them can go bad, and there is also a connector for these pickup coils between them and the TCI that can cause problems as well! The newer 1st generation Ventures switched to a single pickup coil setup, so if it goes bad the whole bike dies...

EDIT: Just looked at your profile and see it is an '87. You have 2 pickup coils...

As mentioned the tach is driven from the primary side of the #2 coil, the tach dropping to zero proves you have an electrical issue.

Strange we just covered this?

Anyways if its just the one cylinder?? Which isn't easy to notice on these when one isn't use to the performance then I agree but, the pickup coil controls 2 cylinders and is more subject to heat related problems such as working well cold not so hot.

My opinion is that it is always worth while confirming solid connections first then pickup coils the TCI