problems starting when engine is warm

 1975 kick start Harley XLCH.  The bike is perfect. No problems kicking
it over. Starts relatively easily.  Until, that is, when it is warm
(not warm weather but when it has been started or used).
For 5 or 6 hours after it has been started (and then shut down) I can
not get it to restart - there is no loss of compression (this is
immense) or increased compression.  Occasionally it will backfire on
the 'live' kick when attempting to restart it but that is as good as it
gets.
Has anybody got any ideas as to the cause of this.  Or better still any
ideas as to how this may be overcome.
Things I have tried: numerous attempts at kicking. kicking with
differing numbers of primer kicks - 1, 2, 3, 4, 5.  Fuel injection and
primer kicks prior to the live kick - 1, 2, 3, 4. Taking out the spark
plugs and allowing extra air to circulate in the cylinders (I think
that the bike may have started once in the past by using this awkward
method, but it is not a constant).
Things I have not tried - bump starting the bike as this would be a
useless format for restarting as any place that I would choose to stop
and turn off the engine would have to be on a hill!!
Think about this now... my bike is constantly refuelled by use of a
fuel can in my garage as I cannot use a petrol station as it will not
restart after refuelling.  And in all other respects the bike is an
absolute dreampiece.

 
Gazzer wrote:

On a warm engine, my compression's definitely increased
and I sometimes find my bike starts more easily with the
throttle part or all the way open.

If there's an auto-advance on the ignition, that might be
worth checking as well, to make sure it's functioning
correctly.

 
    Just a little nitpick, but they are Keihin, and the term is
"constant velocity".


Phil
--
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 Cheers guys.

The carb on the bike is a Keihin (venturi carb) and its workings are
fine.

The points are also set fine and sparking well, as are the plugs - H-D
4R (resistor type)... the spark plugs that I have used on the bike have
never tended to have that 'rusty colour' of a perfect fuel-air mix.
Instead they have always tended to have a slight black-ish deposit, but
having said that the engine runs and sounds perfect when going and a
notable adjustment in the fuel-air mix causes the bike to run and sound
less good... so I have opted for a better running bike than
plug-indicated perfect fuel-air mix!! Surely this should not have
reaching effects into warm starting?

I use choke on start up - generally requiring half choke which is
closed after 1 to 1.5 mins of engine running.

Later this evening I shall try warm starting the bike with the throttle
very slightly open on the live kick and no primer kicks (start with the
easy options first!).  I am a little wary of this method and will
probably report back with a sore head from hitting the garage roof from
kick back, or requiring a new carb from complete backfire through the
system, but its worth a try.

For anyone who knows harley kickers my method of starting it is as
such:

Turn fuel tap on

3 or 4 flicks of the throttle to fire fuel into cylinders

Fuel tap off

3 primer kicks (push kicker to just before TDC then kick hard/fast to
neutral position

'Live' kick - push kicker to just before TDC, hold it there, turn
ignition on, wait (if necessary) for oil pressure light to light up,
kick hard/fast from held position.

If bike doesn't start here I turn the ignition off and give 3 or 4
kicks through from TDC to clear the fuel and start again. This
generally works within 3 goes.

Not when the engine is warm though!!

Any further suggestions are most welcome... afriend of mine has
recently suggested trying electric ignition as opposed to points - he
reckons its a godsend on his BSA.

 

Let's just say it could, possibly, indicate a generally rich condition that
will not help your hot starts. Deposits on plugs removed after normal
running rather than after a true "plug chop" test usually tell you more
about idle adjustment then about full throttle jetting.


We're talking about extremely small throttle openings here, sort of
1/32th inch small.


That's not me, but I have some experience with single cylinder bikes.


On my thumper, I would never ever do something like that (i.e. any
action that adds fuel) if the engine was warm. Kicking for five minutes
is no fun when I'm already half dead riding enduro very badly.

Other things I've done to make life in the woods easier is to clean the
air filter often (it really makes a difference) and use ridiculusly
expensive spark plugs (the ones with a thin center electrode made from
unobtanium).

--
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