We just finished installing new ported heads, new cam, long tube headers. Now when trying to start, you have to give full throttle, then it will fire, but will quickly backfire through the exhaust. won't idle at all. Any sugestions?

We have checked fuel...have 43 PSI at the rail, have spark at all cylinders.

 

What year is the car? I would check the easy stuff and make sure all of the plug wires are going from the correct opti plugs to the corresponding cylinders. Are you positive the timing chain and opti were installed correctly?

 

96 Z-28
We have reviewed the plug wires several times...The Opti-spark only can go on one way due to the clover leaf design and the pin drive. It is possible that I was off on the timing chain, but I really did not want to take that all back apart.

I set the valve preload at zero - plus 1/2 turn. I had someone suggest 1 full turn but that should not make a difference for starting. only maybe some valve noise without enough preload.

 

tune? bigger injectors?

 

Yes on the bigger injectors, 36 Lb (I think) We had the Local dyno guy come over before we tried to start it to change the programing for the bigger injectors.
I have checked the impeadance on the injectors and they are 14.4 ohms.

 

What method did you use to adjust the valves? I'd double and triple check that you don't have any plug wires crossed.

 

Is the SES light illuminated?