351Powered

Hello everyone!

Still having a problem w/ the Mach 1:

Problem: A "popping" noise/small backfire from the carb when the throttle is opened quickly and only quickly. If it is opened slowly the engine will spool up just fine and everything sounds great. The popping happens more easily when the engine is under load. For audio/visual reference please watch this clip:

YouTube - Mach 1 First Run 4 08 09

Car is question:
1973 Mach 1
4160 600cfm Holley
351 C
4 speed

I would really like to get this car to the big show at the University of Maryland (April 26). I'm thinking a valve or timing chain problem off hand?? Please help!! Thank you!!

xrfairmont67

it sound like its a lean backfire. remove the air filter and look down the front barrels of the carby. in the cetre u will see a phillps head screw holding the squirter in . when u blip the accelerator fuel should flow from there straight away. the very first 3-5mm movement it should be spraying fuel. i would first check the accellerator pump on the lower rh side of the front fuel bowl (looking at carby from front of car). there is an adjustable bolt/nut with a spring . 3/8 head . put a spanner on bolt head and nut head and turn out half a turn at a time. start car and check. readjust if needed. other than that it may be the accellerator pump diaphram need replacing..

ziggs

hey mate.

i agree with the idea of a lean backfire but would also like to add check the ignition leads. i had the same set up as you on my 351 as may ppl do and mine was a silicon lead breaking down under load. i replaces the leads with a set of bosch stainless core type and the problem went away.