BSCC- Vapor Lock

David, Cynthia, and Elliot Silvia porsche944 at ids.net
Mon Sep 18 19:37:24 EDT 2006


My two cents-

While I may be new to the club I have had a lot of old cars and trucks, including many Corvairs, and I have spun a lot of wrenches on them.  I know that somone will beg to differ, but everytime I have heard of a problem and it is attributed to vapor lock - it isn't.  While vapor lock was common on very old cars because of the lack of a fuel pump (engines were gravity fed from a tank in the cowl), it simply doesn't happen often on anything with a fuel pump.  It also can't happen when the car is running.  The theory behind vapor lock is that the gas gets heated in the lines and vaporizes causing a non-start problem on a hot engine that has been recently shut off (hot soak condition).  Fuel in motion will not tend to vaporize in the line. 

It does not mean that the problem is not heat related, I just seriously doubt it is vapor lock.  I have gotten Corvair engines super hot and ruined them in the process, but never experienced a probelm with vapor-lock.  

So what to check?
I have seen ignition coils go bad when they get hot, a condenser that goes bad when hot, and bad connections to the ignition.  When this happens again, check for spark.  it is still possible it is fuel related, like a fuel pump problem, so pull off the air cleaner and look down the primary carbs with the engine off, push down on the accelerator linkage and see if you get a "squirt" of fuel, if ya do - it isn't vapor lock.  

Good luck 
Dave

PS - Just recently I had a problem on my porsche that the prosche club members told me was vapor-lock, it wasn't - it was a bad reference sensor.  
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