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Re: vapor lock

To: Jonathan and Carole Quandt <fourqz@earthlink.net>
Subject: Re: vapor lock
From: Dave & Marlene <rusd@velocitus.net>
Date: Thu, 21 Apr 2005 19:45:26 -0600
Hi J,

The classic definition of vapor lock is when fuel turns to vapor on the 
suction side of the fuel pump or in the pump. Fuel on the suction side 
(under vacuum) is vaporized by heat more easily than the fuel under 
pressure on the pump output side. The pump itself getting hot is usually 
the main offender. Since your pump is on the same side as & near to the 
tail pipe, it may get hot enough for the fuel in it to turn to vapor, 
which it can't pump. A heat shield around the pump might help. Later 
Healey cars had the pump moved to the opposite side, away from the exhaust.

Fuel boiling in the carb float chambers can turn to vapor & cause 
similar problems.  Later Healeys had heat shields between the exhaust & 
the carbs. Some have insulator blocks between carbs & manifolds. Usually 
when running down the road there is enough fuel flow & air flow to keep 
the fuel from boiling. Gasolines are seasonally formulated to have lower 
boiling temperatures in winter than summer. Sometimes if you get caught 
on a hot spring day with winter formulated fuel you can get into real 
"vapor lock" problems.

I have a similar car to yours with a low pressure later model pump (SU 
1300 series) in the standard location & no heat shields on the carbs or 
pump. I do have a six blade variable pitch metal blade fan that may keep 
enough air flowing to prevent problems. Possibly the 100M style cold air 
intake helps. The header down tubes are wrapped with a ceramic blanket 
shield. Or maybe I just don't get stuck in traffic on a hot day. No 
problems anyway.

You may have to try a few remedies. A quick temporary try would be to 
wrap some R4 building insulation around suspected problem areas. Make 
sure that the pump is really good but not more than about 3 psi 
pressure, & that the lines & filters are not restricted. The last time 
that I had vaporlock symptoms, the fuel filter was mostly plugged.

No doubt you will get some good suggestions from others.

Dave Russell
BN2

Jonathan and Carole Quandt wrote:
> My 56 bn2 will sputter when the motor is stopped , when hot, and 
> restarted before the car has had a chance to cool down a little.  I have 
> done all the usual replacement coil and condenser . perhaps the fuel 
> pump needs to be moved to a cooler spot or the headers wrapped with 
> something . The heat shield on a 100 is a joke . If it is heat causing 
> the problem, with a component or causing , let's call it, vapor lock  
> somewhere . What is it? Some comments from those among  you who have had 
> similar problems and found solutions through either VooDoo or intellect 
> please reply Thanx, J




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