Going dead at 80 mph

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1971 Mustang Mach 1, M code, 4 speed.
I used the standard ole clamps. Is that a gear clamp? Also I just used regular hose I so far haven’t used corn gas.
+1 on no "corn gas", it eats rubber for lunch. A "gear clamp" is one that has the worm screw engaged in slots on the band, usually tightened with a screw driver. They are my pet peeve for sure and I only use them where appropriate or non critical places.
 
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Blue Springs, MO
My Car
1971 Mach 1, Grabber Blue w/Argent stripes. Original 2V 351C Auto, Tilt, rear defog, Black Comfortweave Interior. Under restoration. Original colors, 4V 351C, 4-Speed, Spoilers, Magnums, Ram Air. All Ford parts.
If your Pertronix is the III, they have an on board rev limiter. Do you possibly have a rev limiter set too low?

I did not see what RPM you are failing at, but if you have 4:25 or higher gear you may be reaching the 4k range at 80 mph. If the Pertronix has a rev limiter that is set too low, it could be causing a problem like that.
 

ROCKET70

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73 MUSTANG GRANDE Q CODE
Petronix has adjustable rev limiter. Maybe it's set too low and I also had years ago one that was defective and it would cut out on me.
Just a thought!
 
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If you do have a PIII, perhaps install a PII which is more reliable IMO. The PIII has good electronics, just poor mechanical design, which is a shame.
However, if you do have a PIII, for sure check the rev limiter setting. If not that, check for excessive movement in the plates. This is for the Ford mode only by the way.
 

Tommyt

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Big Cove AL
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1971 Mustang
Mach 1
I have installed a tach so now I can monitor my rpm range. I’ve also made great improvement with a simple fix. I reseated my factory look plug wires in the distributor. I couldn’t see or feel a problem but one or more must have been unseated. I’ve hit 90 mph without a miss.
The engine turns very high rpm I was close to 3500 at top speed(90) if I cruise at 3k I’m in the 70s mph.
I only lose power on our biggest mountain now. I was convinced I was tip-top I drove app. 45-50 miles with no problem. So I gave her the mountain test. The failure felt different she didn’t give up she was either rich or lean I think I’m real close.
I thank everyone for ideas and input. Future plans are get rid of gear clamps and all new hose front to back. Also not ruling out having damaged my petronix which a 2.
 
Joined
Sep 12, 2015
Messages
5,909
Reaction score
974
Location
SW Ontario
My Car
1971 Mustang Mach 1, M code, 4 speed.
I have installed a tach so now I can monitor my rpm range. I’ve also made great improvement with a simple fix. I reseated my factory look plug wires in the distributor. I couldn’t see or feel a problem but one or more must have been unseated. I’ve hit 90 mph without a miss.
The engine turns very high rpm I was close to 3500 at top speed(90) if I cruise at 3k I’m in the 70s mph.
I only lose power on our biggest mountain now. I was convinced I was tip-top I drove app. 45-50 miles with no problem. So I gave her the mountain test. The failure felt different she didn’t give up she was either rich or lean I think I’m real close.
I thank everyone for ideas and input. Future plans are get rid of gear clamps and all new hose front to back. Also not ruling out having damaged my petronix which a 2.
Awesome! Sounds like you have pretty much solved the issue. Little things can and do, cause BIG problems that are hard to find sometimes.
On your PII, make sure the ground wire is connected and tight, as well as the coil nuts. Also make sure you have a full 12 V powering it. Again, little things.
Glad you're losing those "gear clamps"!!
Keep us posted on progress.
 
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