Holley Carb Tuning on a Mild-ish 289 - Page 5 - Ford Mustang Forum
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Joined: Apr 2006
Location: On the road n NE Oklahoma
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Originally Posted by paul289 View Post
Alright, got the car back on the road with a new mechanical flat tappet cam since I destroyed the roller cam by spinning several lifters. So, back to cab tuning.

Main thing I could use help with is flooding under braking. No, it's not coming out the float vent. I've got a vent whistle in both front and back. It's coming out the boosters. I can tell because when I have the carb removed, and I tilt it forward, I can see fuel dribbling out of the booster. Really, that shouldn't be happening. Is there some anti-siphon passage that's blocked or does the rear float level need to be lower than the arrow on the sight glass or something?
Every 4150 based Holley will run much better on the street with BOTH floats lowered 4 flats below the sight glass or level plug setting. You will not starve the engine by doing this....

The exception being if you are going to keep the throttle wide open in top gear for longer than 30 seconds. In that case you need jet extensions and higher floats. But for 99.99% of us, lower the floats. That will solve many many drivability issues with the Holley dual float carbs.


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Galaxie 500
'65 K code Mustang
& a few '66 GT350's (1970-2012)
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post #62 of 62 (permalink) Old 06-04-2018 Thread Starter
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Just seems like a patch fix, but I guess changing the jetting to compensate will do the trick. I did lower the rear bowl 3 or 4 flats below the center of the sight glass, and that did help a lot. Would it also help surging while creeping near idle in first if I did the same in the front bowl?

Proud owner of a '65 289 coupe. Equipped with Edelbrock Performer intake, Quick Fuel 680HR carb, ported stock heads, 282 Magnum solid cam, Hedman longtube headers, MSD ignition, and decked and ported heads. T5 transmission with hydraulic clutch. Griggs Racing GR350 suspension. 8.8 rear end. Griggs front & Wilwood rear brakes. Many more mods to come!
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carburetor , holley , quick fuel , tuning

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