427 running rich

[SCOBRAC]

Actually I just put it on recently. I had been chasing new engine gremlins for a few months, undersized fan, thermostat issues... I got it all dialed in and it ran ok but it was tricky getting the idle to settle down coming off throttle at a stoplight. It would idle fine after about 30 seconds, but from stopping to 30 seconds after stopping it would idle high, 1100-1200 or so. I have it plumbed to the back of the medium rise manifild port with a tee to the power brake booser. There is a one way check valve between the tee and the brake booster to hold as much vacuum to the brakes as possible.

Both my valve covers have screw in breather / cap holes. I put the pcv valve right into the valve cover with an oversized pcv bushing and it corrected the rich condition / off throttle idle problem. I was concerned about brake vacuum to the booster because I only get 5.5" of vacuum. I haven't checked the manifold vacuum since installing the valve but it doesn't really matter, drivability increased and the braking hasn't suffered.

It's hard to say whether your carb is undersized. It depends on how you drive it and what you want it to do. The 8v Medium Rise engine had a pair of 710 cfm 4160 style Holley's. I started this engine on a pair of 450 cfm carbs I ran on my 428. They were ok. But I knew there was more to be had. I really debated on whether to go for a pair of 600's or something bigger. Vacuum secondary carbs will only ever flow what the engine demands of them so while I knew the 427 could never really draw 1200 cfm there was a reason Ford went with dual 710's...

I decided the 660's would be a good compromise. They are excellent. They really woke up the side oiler. I run them slightly progressive and the 660's open about 30 degrees before the secondaries begin to open. That gets me all open in the front primaries, 1/2 open in the rear primaries before the front secondaries begin to open. I am at 3/4 throttle before the rear secondaries begin to open. At WOT everything is open. The effect is pretty impressive. I have no stumble or bog. Just tons of wheel spin.

I recently acquired a 427 equipped thunderbird with a vacuum secondary 750 cfm 4150 holley. It's a mild 10:1 engine, 280 duration solid cam, etc. It didn't seem like enough carb. I found a old NASCAR 750 cfm Holley reworked to flow 932 cfm.

It really woke up the 427. It acts like a completely different engine.

I'm not big on over carbutration but in both cases the changes were dramatic.