[tripower]

Using an out of the box Delco rebuild 7041264 QJet on a near stock 71 YS 400 motor. Starts fine, idles fine but stumbles coming off idle to accelerate. Not as bad when engine warms up to operating temp. Stock setup using ported vacuum advance and initial timing at 12 degrees. Date code stamped on the box (rebuild date) is 3/28/78. Any thoughts on a fix? Thanks!

[formula kid]

Check the set screw on the secondary air flap it my need to be adjusted so there is more tension.

[1968GTO421]

This link may offer you some help.

[mgarblik]

If the carburetor was rebuilt over 40 years ago, all the rubber parts are NOT compatible with alcohol fuel. You can verify by looking down the primary barrels
and very gently wiggle the throttle from idle to 10-15% throttle opening. (engine not running). You should see an immediate, sharp squirt of fuel from the accelerator pump squirters. Almost guarantee the accelerator pump cup has been ruined by touching alcohol fuel. Only takes a short time and they are ruined. Best way to eliminate future problems is to buy one of Cliff's Q-Jet kits and install it. His kits have all the alcohol friendly rubber parts. Quick fix would be to just replace the accelerator pump cup. But again, you need to get one from Cliff so it will last more than a week. Good luck.

[Kenth]

An original 7041264 will not have a ported source for the ignition vacuum advance since all 1970-74, except 1971 455 H.O., engines uses the TCS system to control the vacuum advance.

If someone added the ported source, who knows what else is done to the carb?