Idle Question (no, not an idle question!)

R

rogtwo@aol.com

Guest
"after it warms up, it will not idle. It stalls unless I rev it up."

To me this sounds like it could be vapor lock (or something close to it).
That is, when it sits hot, some of the gas in the carburetor gets hot enough
to vaporize. This prevents the carburetor from feeding the right amount of
gas until the engine runs a little bit and the carburetor cools back down.
This is certainly not the only possible explanation for your problem, but it
seems like the most likely one to me.

Some things that can aggravate vapor lock are hot weather, or using winter
gas in warmer weather (winter gas boils at a lower temp).

Roger St. John
White '63
Seattle



[Non-text portions of this message have been removed]
 
D

Daniel & Kathy Gibson

Guest
Ok gang...I need to hear from some experience. My amphi has developed the habit
of starting
fine and idling great, but when I restart it after it warms up, it will not
idle. It stalls
unless I rev it up. Seems to be running ok when my foot is on the gas. Any
ideas? The
carbie is not doing anything obviously wrong. Points are new, and the gap looks
ok. No
obvious vaccum leaks or noise. I am leaning towards the coil going kaflooey
after it warms
up, but I would think this would affect it at speed as well.

Help!

Dan
 
C

cptcrnch56@aol.com

Guest
You might check for a vacuum leak. A simple Vacuum gauge will tell you much.

Frank


[Non-text portions of this message have been removed]
 
B

Bill Connelly

Guest
Will it begin idling OK after the engine has run again for a couple of
minutes? If so, then it's very likely the rising heat of the standing
engine (which will be much higher once the cooling system stops pushing the
coolant water around it) boiling up the gas in the carb and/or the nearby
metal fuel lines (i.e. vapor lock).

Possible remedies: Make sure the heat insulating gasket thing between the
carb base and the manifold is still there (it might have been removed and
never replaced during a rebuild). If it is, you could consider adding some
sort of heat shield, like a small pie tin, around the base of the carb to
deflect direct rising heat away from it. Wrapping those metal fuel lines
from the fuel pump with reflective insulating tape might also help, since
the gas could be cooking up in these lines too, seeing as how close they are
to the engine.

~Bilgey~

----- Original Message -----

"after it warms up, it will not idle. It stalls unless I rev it up."

To me this sounds like it could be vapor lock (or something close to it).
That is, when it sits hot, some of the gas in the carburetor gets hot enough
to vaporize. This prevents the carburetor from feeding the right amount of
gas until the engine runs a little bit and the carburetor cools back down.
This is certainly not the only possible explanation for your problem, but it
seems like the most likely one to me.

Some things that can aggravate vapor lock are hot weather, or using winter
gas in warmer weather (winter gas boils at a lower temp).

Roger St. John
White '63
Seattle



[Non-text portions of this message have been removed]


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D

David Chapman

Guest
> Ok gang...I need to hear from some experience. My amphi has developed the
habit of starting
> fine and idling great, but when I restart it after it warms up, it will
not idle. It stalls

This sounds like a blocked slow running jet, it's not an issue when cold
because it's bypassed by the choke but when warm car won't idle. The slow
running jet is the smallest in the carb and first to get blocked, it's often
swarf caused by overtightening the fuel pipe where it goes into the carb but
I once had one blocked by an eyelash ! Just remove it and blow it out with
air - manual shows it's location. Fuel vapour locks almost always happen at
high speeds, common symptons are car feels "held back" and won't go over
50mph, then 40mph etc etc. Of course they are very dependent on outside
temperature, not often a problem below 25c (I think thats about 80f)

It's worth replacing HT leads if original as they can go soft when hot and
give a misfire, don't use the carbon centred ones if you have a distributor
cap with the screw type fitings (the original sort), either use copper core
or use the later type cap where they plug in.

Fuel pump, I agree with Gord, electric ones cause more problems and can be
unsafe, I would never use one, the Solex has a max fuel pressure of about
3psi, the generic pump you guys in the US will buy at Pep Boys will
overwhelm it. There are also issues with fuel filters, prone to leakage and
getting blocked, again best cure the problem by removing what needs to be
filtered.

The magnet on the tank works well but you must never remove it ! Never use
an original Amphicar tap on reverse as the inlet is at the very bottom of
the tank. Probably too late but you can avoid corrosion by keeping the tank
full but there are so many issues with the original tank and design it's
much better to replace it with one made of Aluminum or Stainless with
external filler and connections at the top, that's what everyone does here.

David Chapman in the UK
 
R

rogtwo@aol.com

Guest
David, I'm sorry but I'm afraid I disagree with you on your description of
vapor lock. You said: "Fuel vapour locks almost always happen at high
speeds, common symptons are car feels "held back" and won't go over 50mph,
then 40mph etc etc."

High speeds generally mean high fuel flows. The high flow of fuel means cool
fuel from the tank is always flowing to the carburetor. This usually
prevents the fuel from getting hot enough for vapor lock to be a problem at
high speeds. Also, when the engine is running, gasoline is evaporating in
the carburetor. This keeps the temperature of the carburetor down.

When you stop a hot engine and let it sit, the stationary fuel now has a
chance to heat up. This leads to vapor lock being most prevalent when
restarting a hot engine. You can get vapor lock when the engine is running,
but it occurs most easily when trying to restart a hot engine.

The fuel companies constantly adjust the vapor pressure (or boiling point) of
their gasoline based on the prevailing temperature in the area where the fuel
is being sold. If the vapor pressure is to high for the temperature, cars
will be hard to start. If the vapor pressure is to low, you can get vapor
lock (and excessive tank venting).

Vapor lock can occur even at moderate temperatures if you are using "winter"
fuel or if you are at high altitudes. For example, if you bought fuel when
it was 40 below zero, and it is now 60 deg F (15 C), then you might have
vapor lock problems. And, if you are driving a 10,000 feet, the lower
atmospheric pressure makes it easier for vapor lock to occur.

The situation you describe of the car feeling "held back" sounds more like
fuel starvation due to a blockage. Or, if the temperature is not too far
above freezing, it could describe carburetor icing.


[Non-text portions of this message have been removed]
 
D

David Chapman

Guest
Roger, I don't disagree with anything you said re vapour locks in carb when car
has been left standing, that is a problem with Amphicar and is why they take a
few more turns of the starter when hot than cold. At the other end of the scale
vapour lock due to carb icing isn't going to be an Amphicar problem but
certainly is on other cars. The hesitation when hot is a specific Amphicar
symptom and is vapourisation. It's because the fuel line is routed through the
car in some hot places (past transmission - over top of engine etc) as the flow
is not high then this warms up the fuel and when it hits the carb it begins to
boil, the carb runs much hotter than it should because it sits on top of the
exhaust manifold, in other applications of the Herald engine there will be
significant forced airflow at high revs/high speed which cools the carb but
Amphicar has just the fan. The factory fitted a heat shield under the carb to
late European cars to help reduce the problem.

Two other ways to fix it, a T piece at the carb with a restricted return to the
tank is the German way, this keeps a circular flow of fuel which keeps it cooler
and it also smooths the pressure peaks as the pump pumps, a good thing. I've
always got around the problem by insulating the fuel line.

Fuel vapourisation is much more a problem in Europe where a gallon costs over $5
because it's cheaper for fuel companies to add the additives that make vapour
locks more common.

David Chapman in the UK



[Non-text portions of this message have been removed]
 
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