Going through the same thing. When its hot out and my engine is about 190F, the AFR on the gauge goes into the 12s-11s during an interstate cruise. The damn fuel vapor makes it go rich while it's running. I blocked off the heat crossover with 321 stainless. That helped a lot but not completely.
I'm trying a 1/4" open spacer between my 750DP and RPM. If that ain't enough, I'm going 1/2" open phenolic spacer. I ran a 1/2" nitrous plate under a Q-jet on the same intake on my previous motor. A nitrous plate is basically an open spacer with the spraybars in the middle. That engine was 9:1 400, XE274 cam, mild ported 670s. 10" converter and 3.90s. It loved the open spacer. The idle vacuum was 10-12", but otherwise the open spacer worked. Especially when the solenoids opened, LOL.
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I could explain all this to the girl at the parts store, but she'd probably call the asylum.
White '67 LeMans 407/TH350/Ford 3.89... RIP
Red '67 LeMans. 407/TH400/Ford 3.25
Last edited by chiphead; 04-30-2026 at 06:18 PM.
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