Issues with the Mach 1

67fastbk

New Member
Jun 6, 2018
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St.louis
So a little basic info to start with....dads car is a 69 Mach 1(original owner), 351W, FXM trans, mild cam, Performer intake, roller tip rockers, 600 Holley carb, Pertronix II with Flame thrower coil. Car had been driving great with no troubles. One day he calls and says the car is having some troubles, it wants to stall and die at stops. He was driving on the highway, ran it up to around 90, let off the gas and coasted down the exit ramp....applied brakes and stumble stumble...die. Car fires right up and runs good until you hit the brakes at a stop. So we check the brake booster for a vacuum leak and bingo problem solved. Replace the booster and everything's alright.....right? Not so fast. He calls again and says it runs even worse now, says it won't hardly run at idle and dies immediately when put in gear with the brake on. So we check for vacuum leaks and all is good. We start to dig a little deeper...checked timing and compression...both good, all cylinders were within 5 psi of each other. We swapped a 750DP on it, too much carb i know, but it was a known good unit.We have good fuel pressure and even ran it with a remote electric fuel pump, no changes. When we would adjust the idle mix, the right side adjustments made zero changes to the engine while running all while still pulling 13-14" of vacuum. So we open another beer to think about what's going on, give it another once over and try it again. Car fires up and runs good, drop in gear...stumble and die. Torque converter? Maybe. Fire it up again and instead of putting it in gear we turn the A/C on for a load on the engine...it does the same thing....stumbles and dies. WTF!?!?!? So now we're really kinda stumped, never ran into an issue like this. We start looking at the valvetrain. I readjusted the rockers and it seemed to improve but it still dies with a load on it. Checked the rockers again and they were out of adjustment. Now we have two valves that will not adjust at all, valve is fully closed, the nut is totally tightened down and the pushrod is still loose. So now i'm wondering if a cam lobe is going bad. What's your thoughts?
 
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