I have a Zenith 601xl with 2700 corvair that I am getting ready to start phase 1. When doing ground runs

the fuel pressure fluctuations & drops off after about 15 to 20 of minutes of running. I have the fuel 

system set up per ww's install manual. I am using andair fuel selector & gascolator & facet fuel

pumps & ma3-spa carb. I would like to if anybody else has had this problem & a method to solve it.

I suspect that I may have vapor lock. Any ideas on shielding for fuel pumps & gascolator would

be appreciated.

Thanks for any replies in advance.

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The floor of the 601 can be pretty transparent to the heat from the exhaust.  If your fuel pumps are bolted there, they can be transferring a LOT of heat to the fuel.  The stock location for the gascolator is also a terrible place for picking up exhaust heat.

Things I did:

1)rearranged the fuel system to get the fuel pumps away from exhaust heat.

2)used some reflective insulating tape that I got from Autozone on areas that were close to the exhaust.  Also, wrapped the gascolator

3)made and installed a set of swiss mufflers.  A roll of wire mesh that clamps to the end of the exhaust, wrapped in a couple layers of fiberglass roving and then a layer of sheet aluminum.  Mine are only 18" long, but this had the most effect, even making the cockpit cooler.  The FG insulates the aluminum so that you can touch them right after landing.  They also make the cockpit quieter.  I built them out of scrap that was left over from other projects.

I installed a heat shield between the exhaust pipe and the gascolator.  It connected to the exhaust pipe with a pair of large hose clamps, and the shield "stood off" the exhaust pipe by about half an inch. 

I also installed a larger heat shield (which I painted white) between the fuel pumps and the engine, and ran a blast tube to it, with cooling air exiting out the bottom.

A photograph showing these can be seen on page 15 of the January 2015 issue of Experimenter magazine here. 

- Pat


no vapor lock with this WW inspired system

What kind of numbers are you seeing for fuel pressure? When you say the pressure drops off do you mean it goes to zero? Does the engine quit?


Fuel pressure is about 4 to 6 psi when running. It will start to fluctuate after running 15 to 20 minutes 

& sometimes go to zero & engine stops & sometimes slowly will come back & run for a while & fluctuate 

drop off again.

At first I thought it might be an instrumentation error, possibly the fuel pressure sender overheating, but if your engine is quitting something else is going on and I don't think its vapor lock.  I've operated my Corvair for 800 hours with extended grounds runs on 90 degree days waiting in line at Oshkosh and have never experienced vapor lock.  Instead of seeking advice from amateurs like us I suggest you call William directly at 904-806-8143.

I agree ask the real expert!

I recently developed an air leak at a fuel fitting just behind my Andair Fuel Valve which is located 16 inches above the cabin flooring on my console.  This high spot did not leak fuel while sitting or running.  I had to remove the fuel line and pressurize it while under water to find the leak.  It was sucking air along with fuel when running.  The fuel pressure varied widely, the fuel in the fuel flow test at the carburetor was half air as seen thru a clear tube extension, the fuel pumps were clacking as when not fully primed and the engine died at idle.  After repair I had to prime the downward part of the fuel line just before attachment to the rear of the fuel valve with 24 cc of fuel to get rid of the air in the line or that bubble will remain during operation.


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