If it ran fine for 15 seconds then it shouldn’t be the pushrods installed incorrectly. It would do it instantly.

Did you use a manual and follow step by step instructions? And did you use a tq wrench?

 

i did use the manual and followed step by step. I bought a torque wrench specifically for the install.

 

Did you install a tuner with a 1200 cc tune?

 

I bought a power vision 4 and installed the tune then sent to the shop which is a power vision rep and had them make sure it was correct

 

I did the same build on a 883 Iron and used a PCV tuner and had problems with the way it ran. It didn't want to idle. I found that I needed to remove the tuner and take it to the dealer for an ECM update. This update told the stock 883 computer that the engine was now a stock 1200. Afterwards I installed a better intake and exhaust and put the tuner back and it runs great now. The tuner alone won't compensate for a 40%+ increase in engine volume. The download at the dealer took half an hour and cost $60.