Volkswagen Repair: 1979-vw super beetle, 1600 air-cooled, mass air flow sensor, mass air flow

Question
I have a 1979-vw super beetle, 1600 air-cooled.  The motor was runing great and and then just shut down. Now it will start but has low power.  I have replaced the temp sensor and the mass air flow sensor.  Checked all the injectors and wiring no grounds that I can find.  When you rev the motor up it will backfire out of the # 3 injector. Not sure what to do at this point.  And it blows white smoke out the tail pipe. Any help you could provide would be great.

Answer
Hi Dody;
If it were a water cooled VW I'd say it had coolant in it.  At the very least it sounds like more than a little moisture, like water...could it be condensation?  How can it backfire out of the injector?  Does it backfire out of the intake manifold?  If so, I would say there is a bent valve, or broken seat on the intake valve for that cylinder.  Can you do a leakdown test?  Shop air of 100 psi is necessary.  A compression test won't tell you enough.  My guess on the smoke is that there is some unburned air/fuel mix that's coming through the "secondary air circuit" into the combustion chamber, and it's got enough water in it that it will make the car smoke, with a white colored smoke.  The only way to tell for sure is to do a leakdown test.  I hope you have the tools for that.  If not, they can be rented.  Both the air compressor, and the leakdown tester.  Has the engine been rebuilt recently?  The low power thing sounds like running on 3, not 4.  Sorry, but it sounds mechanical, not fuel, or ignition related.  Good luck, Dody.