backfiring, Please Help

[Carolyn's 911]

Have a 1970 911T with a bad backfiring problem. Re-built the Webers (.055 jets), new cap, points, plugs. Set timing to proper spec. Still have backfiring above 3000 rpms. Other issues that might give a clue: when started cold, exhaust has considerable white smoke, no smoke when warmed up; can hear a tapping noise on right side cylinder bank; my skills at balancing the carbs are negligible; backfiring gets progressively worse above 3000 rpms; bacfiring is in all cylinders and is mostly through carbs. Would greatly appreciate any words of wisdom, as I am brand new to Porshe and extremely frustrated/lost. Thanks

[Zendalar]

Did you remove the carbs? If you did, did you install right gaskets between the intake manifolds and carbs? I had to put gasket goo on mine because it leaked even though it had new gaskets.

Dunno about that tapping noise, mine does the same. I have to still re-bush the shafts because my carbs shaft leak the #6 cylinder end.

BTW, there are great instructions in this website, well use search function on the BBS and you will find how to adjust the carbs.

[Rot 911]

Backfiring thru the carbs is normally an indication of too lean of a fuel mixture. Backfiring thru the muffler generally is too rich of a mixture. I would recommend you have the fuel mixture checked. And, as pointed out by Zendalar, make sure you do not have an air leak at the intake manifolds. This will also result in too lean a fuel mixture. The white smoke on start up is normal. The tapping noise on the right cylinder banks is probably the valves. When was the last valve adjustment?

[Carolyn's 911]

Zendalar,
Put new gaskets on when I rebuilt the carbs. How do I tell if I have a leak at the carb/intake joint?

Kurt V,
Don't know when the valves were last adjusted, but probably has been too long. I've purchased what I think I need for this job. Looking for time now. How does one check the fuel mixture? Can I do it myself, as my budget for this project is limited?

Thanks to both of you.