new carb dieseling

[chengny]

oh boy I cant wait, I have this problem and I have a manual choke 1406 carb, my question is if I have no idea of the history should I rebuild first ? as long as the choke is shut it runs (sounds) good when I push on the gas

Are having trouble with dieseling or pre-ignition knock/ping?

Dieseling refers to the tendency of the engine to continue to run/rattle on even after the ignition switch has been moved to OFF. It often ends with a loud backfire that startles the neighbors and makes dogs bark.

Pre-ignition ping/knock is experienced while the engine is put under a load (i.e. when you push on the gas). It isn't as embarrassing as the run-on and backfire associated with dieseling but is more harmful to the engine.

Both conditions can also often be accompanied by kickback on hot starts.

In any case, the root cause for both conditions is almost always overly advanced ignition timing. And the solution is also the same for each - retard the timing in tiny increments until the pinging and or dieseling subside. Drive around for a week or two and occasionally really lay into the gas while listening for the slightest ping - turn the radio off. Also the truest testing is done on the hottest days.

Once you're sure the applicable condition is rectified by the lack of symptoms, verify that you haven't overly retarded the timing. While slightly retarded timing is not harmful, does have a noticeable effect on performance.

If you feel there is a reduction in performance give it a shot. On a hot day, try advancing the timing a little bit towards where it originally was. Repeat the week long test driving process; if it pings, set it back. If it doesn't, you can go for even more advance or stop there, it's up to you. This procedure is the basis for what is known as setting your ignition timing "by ear".

IMHO - this is the only way (by ear) to time a SBC (HEI with non-ESC/EST) anymore. The timing specs for these engines were provided by GM 30+ years ago. A lot has changed since then. For just one example, gasoline used to contain lead and did not contain methanol.


Rotor turns clockwise within the distributor. Rotate distributor counter-clockwise to advance timing, clockwise to retard.

The big font is just to help me remember.