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Re: [Tigers] Vapor lock/fuel percolation

To: "'awtiger'" <awtiger@cox.net>, <tigers@autox.team.net>
Subject: Re: [Tigers] Vapor lock/fuel percolation
From: " Ron Fraser" <rfraser@bluefrog.com>
Date: Fri, 30 Sep 2011 11:20:05 -0400
Andy
        Any time you think you have a carb problem the 1st thing to check is
your timing and advance curve and make sure the timing always comes back to
the initial timing point.  I have seen this advice in a few articles that
most carb problems are really ignition and timing problems and I now agree
with that statement.

        I have been working on some similar problems with my Tiger, low rpm
feels wrong, lethargic and wanted to stall until I step on it then it goes.
My problem was the after market fuel pump gave up after 20 yrs.  Fortunately
it totally died in my garage and not out on the road.  I suspected the carb
idle circuit and the main jet where also contaminated.  I found many small
particles of whatever in the carb.  I had to remove and clean the 2bbl carb
plus I replaced the fuel filter.  I tapped on the removed fuel filter, more
particles fell out.

        The engine now feels and sounds better at low rpm and idle but it
still needs more work.   I need to tune the carb and engine to run better on
the 10% alcohol fuel we are now forced to buy here in NY State.

        Alcohol can be good and bad in older cars.  Good at cleaning
deposits out of the fuel system and give a bit of an octane boost; bad that
it can also dissolve rubber parts, gaskets and some older fuel filters, so
I've read.  The point here is to be aware of some of these problems with
alcohol fuels.

Good luck with your situation.   It most likely is a combination of several
small problems that you need to step through which you are doing.    Assume
nothing and take nothing for granted until you find the real source of the
problem.

Ron Fraser


-----Original Message-----
From: tigers-bounces@autox.team.net [mailto:tigers-bounces@autox.team.net]
On Behalf Of awtiger
Sent: Friday, September 30, 2011 6:01 PM
To: tigers@autox.team.net
Subject: [Tigers] Vapor lock/fuel percolation


Guys:

After all the stuff I've done to the Tiger ignition-wise to get it to quit
stalling, I'm finding myself starting to consider other possibilities, such
as vapor lock and fuel percolation.  To make a long story short, the car is
leaving me on the side of the road when it's up to operating temp and warm
outside.  It caughs and sputters and won't take any throttle at all at low
rpm.  When I coast off to the side of the road and take off the air cleaner,

I'm seeing what I would consider to be a large amount of vapor coming from
the overflow tube (Holley 465 4 bbl).  It also periodically spits fuel from
the center squirter down the throat of the carb.  From what I've read on the

'Net, this sounds like a classic case of fuel percolation.  One other
thing...the car will always start back up and run, but will not take any
throttle or any low rpm load.  Also, when I manually open the throttle, I am

rewarded with fuel squirts (at least I know it's got fuel in the carb at
that point).

What I can't figure out is, if it is percolation, what has changed to make
it do that?  I've made no changes to the fuel system of the car.  In fact,
until the recent ignition tune-up, I'd made no changes to the car for many,
many years.  It's never done this before.  The car is also running at the
same temp it's always run at.  Could the gas we're getting nowadays be
responsible for this?  I always run 91-octane premium (real gas, no ethanol)

and have for years.  I've heard there is such a thing as "winter mix gas"
and "summer mix gas" and that each have a different temperature at which
they volatize.  Due to some serious drains on my time lately, the last time
I filled the car up with fuel was in May.  Could I just simply have a load
of "winter gas" that volatizes at a lower temperature?

Any suggestions???  Please somebody send me to school here...I'm beginning
to feel really stupid.

Andy Walker
Edmond, OK
B382001600LRXFE
TAC #740
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