Idle's good...runs like crap!

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RocketFoot

Stangin' ain't easy but somebody gotta do it!
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Location
Latrobe, PA
My Car
1971 Mach 1
Well, this problem just won't go away! It killed all summer's cruising and we still can't figure out what is wrong.

The car will idle fine but starts to miss when you give it gas to accelerate. We have replaced the plug wires, new coil, added electric ignition module for the Pertronix dist. and even rebuilt the carb. There are 2 things left to do...new carb and new plugs. Visual inspection of th plugs seemed good so Dad thinks there might be blockage in the metering blocks in the carb. So we need some ideas of where to go next...

 
Hey Rocket,

A few weeks ago, I had a similar situation on my 73 and found that my glass type filter had a slight blockage. It would allow just enough fuel to let it idle, but not enough for when in gear. If not the fuel filter, then blockage in the carb system or sticking accelerater pump. If you don't already have one, I'd put a fuel pressure gauge to monitor how much psi is going into your carb. I hope this helps bro!

 
Hey Rocket mine had a miss a couple months back. I replaced plugs, wires , new fuel filter , rebuilt carb , after all that it still did not fix it, I found out it was fuel pump was going bad. I use clear filters and at idle it would fill the filter and any increase in speed filter would drain and fuel would just barely dribble into filter, replaced pump and all is fine. Might be worth checking

 
Well, this problem just won't go away! It killed all summer's cruising and we still can't figure out what is wrong.

The car will idle fine but starts to miss when you give it gas to accelerate. We have replaced the plug wires, new coil, added electric ignition module for the Pertronix dist. and even rebuilt the carb. There are 2 things left to do...new carb and new plugs. Visual inspection of th plugs seemed good so Dad thinks there might be blockage in the metering blocks in the carb. So we need some ideas of where to go next...
Does it smooth out once you have reached speed?

If it hesitates on acceleration and smooths out could be

your accel pump needs adjusting. What is the idle vacuum?

mike

 
+1 on adjusting the accelerator pump. I had a similar problem and adjusting the acc. pump was the culprit.

 
What carb is it?

Do you have access to a known good one to temporarily switch it out with?

That'll narrow the guessing game considerably.

 
Since everyone else mentioned fuel issues, do you have the dual vac. advance on the distributor. I reversed my vac. lines by accident once and had much the same problem. The next question is, is the vac advance working?

Steve

 
We do have a new carb sitting around to try. The fuel pump could be a place to look also! Thanks for the ideas, guys...that will give us some stuff to look at today!

 
Barry, could also be

1- sending unit filter as many of these cars have rust inside of the tanks

Since you have a carb swap it

Stick in a clear filter

Personally I think it is number 2 or 3

2- curse of the coupe, coupe is P.O.ed your not working on it

3- your dad builds and races them Chevy motors... just saying, it's hard to get the Chevy cuties off your hands!!!

 
Barry, use a gas can and hose and eliminate the fuel system (tank and lines) by running it off the can. Sometimes all these hi-tech fixes have you chasing your a$$, sometimes you just have to go old school on the problem:D

 
You know, I can't actually say it's just high rpm's...I can rev the engine and it sounds good. It misses when you pull out into the street and hit the gas to accelerate. That is when it misses and has lack of power. Idling in park or neutral, it runs and revs fine.

 
Another tip... do ONE change at a time, then test...

(BTW...Chevy cooties...ewww)

 
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Like Don said do not overlook the sending unit, been there and done that. You might take compressed air and blow back through the fuel line, from the pump to the tank, into the tank. Be sure and open your gas cap! Just do a small blast and listen for the air bubbles in the tank. If there is crud on the screen it should blow it off, for a little while. Do you still have your carbon canister connected? Is the tank still vented correctly? Could be a starvation / vapor lock issue.

 
Have yo bypassed the resistance wire for the Pertronix? Remember all my misfiring. I could get the car to idle fine but always had trouble on the street make sure you have a good 12v going to the pertronix.

 
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How old are the plug wires? My BroncoII did the same thing. I had cooked the plug wires and it increased the resistance to the point it was arcing back at the coil and would miss under load.

 
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It has new plug wires and the Pertronix is getting a full 12 volts from a new MSD digital ignition module that we just installed. All systems are go in that department.

 
It has new plug wires and the Pertronix is getting a full 12 volts from a new MSD digital ignition module that we just installed. All systems are go in that department.
Try my old gas in a jug. It will elimate the complete fuel system.

 
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