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Idle's good...runs like crap!
#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...

[Image: 1gq8uo.png]
1971 Mach 1 - 306cid/C4 Bright Yellow
"Just relax, I've got a friend named Felix who can fix anything!" ~James Bond
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#2
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!
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#3
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

[Image: 2zdx09d.png]
Yea,Tho i cruise through the valley of the shadow of rice,I will fear no Turbo,For Torque art with me.Thy rods and crankshaft,they comfort me. Big Grin Robert
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#4
rocketfoot;39337 Wrote: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

[Image: 1_11_11_13_11_50_27.png]
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#5

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

71 Mustang fastback
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#6
Do a compression drawdown also. Valves will give you some weird problems.

[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
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#7
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.

Pete - MotoArts Decals and Signs
'71 Sportsroof 351C-4V/4-speed - FINALLY under construction - no, wait, on hold again...
'90 Mustang 7-Up 5.0 ragtop, rolling beater
'66 Sunbeam Tiger Mk.IA, survivor
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#8
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
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#9
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!

[Image: 1gq8uo.png]
1971 Mach 1 - 306cid/C4 Bright Yellow
"Just relax, I've got a friend named Felix who can fix anything!" ~James Bond
  Reply
#10
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!!!
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