Chevrolet Repair: 1999 Tahoe, distrubutor, leaky valve

Question
Sometimes when you start the Tahoe it will backfire through the engine? A cloud of smoke will come out as well. We're getting ready for vacation and driving the truck. What should I check?

Answer
Hi Mark,

Under your distrubutor, you have a set of weights.  These are your advance timing weights.  They are spring actuated and sometimes get rusty or dirty.  When that happens, they will bind up and not retract or operate correctly.  This affects your advance timing.  The smoke is caused by unburned fuel and a little oil passing out the intake valves (out of time).  To check, take off dist cap and operate the weights by hand.  Are they freely operating?  Use WD-40 or equivalent to free up the weights.  

Your timing chain could be out, but this would be more often.  

Is the smoke blue or black?  Black is fuel (carbon) and blue is oil.  If oil, it could indicate leaky valve stem seals.  This blue smoke caused from this happens every start up, at take off from lights, and comes out the tailpipe.  

I would focus on the distrubutor weights.

C J S