Q-Jet tuning? Timing? Vacuum?

[Steve1957]

My low-milage 72 CdV with a Q-Jet. Ran pretty well for 2 yrs after I got it. Then, carb started getting pretty choppy after start up, as if fitful fuel flow. Pretty sure orig. carb, don't know how many rebuilds, I had it rebuilt about 1.5 years ago. Still ran choppy, mech. said he was having trouble getting timing right. 3 return visits for that, never really fixed. Worse in the cool months (in FL), but usually smoothed out after 10 mins. or so. Because choppyness persisted, took it to a restoration shop with a good rep. They thought it was vacuum first. Then cleaned out int. and ext. fuel filters. Still choppy. 3 visits there, too. Still choppy. I know Q-Jets can be a mystery. So, over 2+ years, I've heard "rebuild", "timing" and "vacuum", all addressed, still choppy. Again, smooths out as engine warms, but very annoying. Some backfiring. Thoughts? Thanks!

[hornetball]

How's your timing chain?  If it's original, it's way past time to change it.

[savemy67]

Hello Steve,

Your post makes a few mentions of the problem resolving when the engine warms.  If there is a correlation between temperature and the problem, I might first verify that the choke is working correctly.  Have you removed the air cleaner and observed the action of the choke at start-up?

An improperly adjusted choke will exhibit signs such as stumbling and hesitation when attempting to drive the car within the first few minutes of engine start from cold.

Respectfully submitted,

Christopher Winter

[DeVille68]

Hello,

what is the air fuel ratio? I would tend to say that the mixture is not right. Too lean or too rich. Check the adjustments of the various linkages. It is not easy to understand to choke system and to set it up correctly. The shop manual has detailed information in which sequence you need to adjust there. Follow every step precisely and it should work nice. Check initial timing and idle speed too.

Best regards,
Nicolas