motorcraft 4300 carb info

[Tom Goldman]

The biggest issue with this carb other than it's relativly poor flow numbers, and the availability of decent cores, is the accelerator pump opperation . ...While this isn't an issue with a clutch or transbrake , it played hell with my car while I tried to run on the foot brake. .......I really could not count on a consistant launch or 60' time untill I gave up and went on the chip for the launch. .....Other issues are proper spring tension for the secondary air valve and making sure it does not stick. ....The acc pump hesitation and air valve were issues on these carbs from new, I've been working on them at the dealership since the mid 70's, and have a lot of service bulletens pertaining to driveability issues. .........Jeffs experiance with air bleeds may be unique to his "altitude" location....I've found the secondary air bleeds to be responsive to changes, particulary when we get the mineshaft air conditions. .........The secondary fuel passages definitly need attention,as they are small in relation to the metering tube. ........Definitly use only the large, single needle and seat. ....Do not use the secondary needle and seat as it will cause flooding when running over 3 or 4 psi. ..........I also dont use the power valve, but use a jet in its place. this will only work using a revlimiter on the launch........ Good luck, it only took me 4 years of playing with this carb to get the car to go 1.00 under. ...When I put on a Holley 650 out of frustration , when I built the car several years ago, the car immediately ran better than 1.10 under.......There is no easy road whith this combo. ........Tom