Did some repairs now I have a backfire, why?

[mike911]

A friend is helping address a few issues, oil leaks mostly, replaced valve cover gaskets top and bottom and adjusted the rockers. 1966 911 2L.

Also, replaced a weak oil hose and decided to do a tune-up, so new plugs (NGK BP 6ES) on the suggestion of several members on the forum, cap, rotor, condenser (Bosch) and points (Bremi). Set the gap according to spec for a 66 on the plugs and points. The wires looked good so I did not replace them, however, upon removing them from the distributor cap two of the tips remained lodged in the cap.

Removed and cleaned them, then re soldered. Set the timing and dwell, the car sounded good until it warmed up then it started to backfire a bit like a "popping" sound, not bad but intermittent, more annoying than anything because it did not do this prior to.

Double checked the spark plug wires and everything seemed in order so we took the car for a good drive. Nothing unusual during the drive, drove it up to temperature and then got on it a bit more, up to 6000 RPM's and no sputtering or backfiring along the 30 minute drive.

Returned to my shop and checked the oil and while it was idling it began to "pop" intermittently again?

Based on the work indicated what could be causing this popping noise?

Opinions and ideas appreciated as always,
Regards,
Mike

[SIMI BOB]

I would suspect a clogged idle jet, which has nothing to do with the maintenance you performed. Pull them out and look for an obstruction in one of them.
Bob B

[mike911]

Thanks for the reply Bob,

More research identifies poorly balanced carbs including Bob's suggestion of clogged idle jets as a possible source of the problem, can this happen at any time as the air cleaner was not touched?

I should note that idle is pretty consistant when cold but after a good drive when the car is warm I have noticed the idle increases from 11-1200 to approximately 14-1600, this has been happening since I purchased the car, so not a new issue.

Another possible culprit might be "poorly adjusted valves", after we adjusted them we checked and double checked them, I realize that when tightening down the outer nut it is possible to have the adjustment screw move out of adjustment and throw the position off even though we were careful, is this a likely reason?

So before considering a complete carb adjustment is there anything I may be missing that should be checked?

Thanks again,
Mike

[Frank Beck]

???
It doesn't get any easier than a carb/linkage sync/adjustment. If you're going to play mechanic that is one of most essential parts of a tune up. And always mandatory.

BTW: If any of the valves required more than ... say... 30-45 degrees of tightening, that is an indicator that they may have been adjusted too tight. Valve adjusters usually only require a slight tweak, if at all.

Good luck.