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WHAHOOO! I have been chasing this one around for months now, trying everything from timing, to fuel pump, to exhaust blockage, to ignition system. At work today I had a brainstorm in response to some info someone posted for me on another board. I went back in and spaced my jets ## further apart and compensated for that change. Before I could not get it above 4800rpm without it breaking up and only building spotty power. Had it to 7000rmp tonight just as smooth as can be! Ok, better, just had to vent!

67 mustang coupe
70 mustang mach 1
88 mazda/ford mx-6
 

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Congratulations!

I had the same problem once and after many trails and tribulations found it was just plugs gapped a little too wide.

"If you're under control you're not going fast enough"
Parnelli Jones
 

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Sorry, I just don't seem to get anything today. What do you mean "spaced jets ## further apart and compensated for that change" Just curious, because I haven't touched my carb. It's Holley 600vac calibrated to 77or 78 318-360 Mopar van. I can't get it past 5000rpm either. Bottom end is good. So I am trying to learn more before changing jets.

Door handle first when cornering
 
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You have primary and secondary metering jets (2 of each per side). They come in different ##s which basically means size of the hole and hence how much fuel is mixed with the air. I had mine spaced 4 apart. Meaning my primarys were 4 ## smaller than my seconds. I went up 2 on my seconds and down 2 on my primarys. There is a holley tuning book out there somewhere (yellow softcover 110 pages or so) that tells you all sorts of stuff.

67 mustang coupe
70 mustang mach 1
88 mazda/ford mx-6
 
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