Hi everyone, I just changed the stock intake manifold 2bbl to a ford cast iron 4v intake on my 72 f100 390. I am having a problem of back firing thew the carb when trying to start but wont start. The back fire is more of a wwhhhooottt than a bang and the timing is set to where it was before at 12 deg adv and im positive im not 180 deg off along with checking the spark plug whires are on the right cylder. Im using a holley 500 2bbl on it with an adapter plate but did the same thing with the 4 bbl on it? any Ideas please help

 

Timing. Valve train

 

Sounds to me like it's off 180 degrees , easy to do , i'v done it myself a number of times when i just knew i had it right. Ha ha , almost every time i pull an engine apart and make changes with the dist.

 

i'LL bet my left nut you have dizzy 180 out , bring timing to TDC pull dizzy rotate engine back to TDC (1 turn ) put dizzy back in .

 

Yep. Either rockers adjusted too tight or dizzy 180 out. Ya have to make sure #1 cylinder is on compression stroke when dropping the dizzy.

 

One tooth off could do it try retarding your timing.

 

SOMETHING we've all done well okay some guys have me too. Check that your pushrods are all seated into the rocker arm cup. These damn rods will slip out of the cup socket very easy and go unnoticed then putting on the valve covers.. orich