Car starts good, idles well and runs fine up to a point. When accelerating it stumbles and hesitates just prior to shifting especially noted when shifting from 2nd gear to 3rd and 3rd to 4th. The carb is re manufactured and has less than 500 miles on it. I have checked float levels, accelerator pump, fuel filters (both carb and fuel line filters), disassembled vacuum secondary diaphragm, checked timing and all idle circuits. The only anomaly I have found is the secondaries not opening. I tested this by attaching a wire on the secondary diaphragm rod and noting that it did not get pushed down after several spirited drives. During these drives I purposely got the rpms over 4000 when shifting from 2nd to 3rd. After 4 or 5 attempts of driving like this the test wire did not move. I then got a Holley secondary spring kit and tried several springs with no change on the test wire. The secondaries still won't open.
When I disassembled the diaphragm I did not find any tears or damage. I tested it by lifting the plunger and plugging the vacuum hole with my finger. The plunger held and did not move until I released my finger from the vacuum port. After remounting, I checked the secondaries by moving throttle to WOT and moving the secondary lever by hand. I noted that the secondaries seemed to move through full range, I also noted that diaphragm plunger moved accordingly as I exercised the secondary lever. Two additional points; this carburetor is on a Ford 302 in a car that weighs about 2300 lbs., also when checking the secondary diaphragm I could not find a secondary check ball installed. Not sure if missing check ball could lead to my problem. I am at a loss as to what could be the reason that the secondaries are not opening while driving. Thanks for any help you can offer.
Tony
When I disassembled the diaphragm I did not find any tears or damage. I tested it by lifting the plunger and plugging the vacuum hole with my finger. The plunger held and did not move until I released my finger from the vacuum port. After remounting, I checked the secondaries by moving throttle to WOT and moving the secondary lever by hand. I noted that the secondaries seemed to move through full range, I also noted that diaphragm plunger moved accordingly as I exercised the secondary lever. Two additional points; this carburetor is on a Ford 302 in a car that weighs about 2300 lbs., also when checking the secondary diaphragm I could not find a secondary check ball installed. Not sure if missing check ball could lead to my problem. I am at a loss as to what could be the reason that the secondaries are not opening while driving. Thanks for any help you can offer.
Tony
