vapor lock, and more

Bob Nelson majordad at
Tue Aug 11 01:05:13 PDT 2009

Drew, first things first, if the motor wouldn't turn over and you had 
gas squirt out of one or more cylinders after you pulled the plugs, it 
was hydrostatic lock, not vapor lock.  Hopefully you only had one 
flooded cylinder.  There are two requirements for this to happen.  
First, you had to have gas flow out of your petcock without vacuum 
applied to the petcock  (or the petcock is in the Prime position, if 
that is the case switch the petcock to the normal or run position).  The 
second requirement is a stuck/leaky float valve in the cylinder involved 
allowing gas to over fill the carb and drain straight into the cylinder.

If you are lucky the flooded cylinder was one of the outside carbs.  I 
say lucky because I am pretty sure you can pull the float bowls without 
pulling the carb rack out of the engine.  If so, you can make sure that 
the float is free to move and not stuck open.  If it is free to move, 
then after putting the float bowl back on, I would tap the float bowl 
repeatedly as I put the petcock in prime to try to help the float 
overcome any stiction and hopefully float and thereby close the float 
valve.  If the float is stuck open, you will need to disassemble, clean 
and carefully watch the first couple of times you start the bike to make 
sure your cylinder doesn't lock again.  If you are unlucky, bad things 
can happen after hydrostatic lock.  You could end up with bent valves.

Anyway, if this occurred out of the blue and not immediately following 
some carb cleaning and reassembly, you might have fallen victim to what 
I suspected happened to me.  This March I rode from Charlotte to Florida 
with some friends after not having any problems for a very long time.  
The next morning I had a cylinder locked.  I attributed it to 
contamination from running way down into the reserve on my fuel tank and 
running some crud through that partially blocked the float valve open.  
After I cleared the cylinder and rode that day, the problem didn't recur.

As far as follow on leaking not associated with the locked cylinder, 
that would have to come from a leaking hose or the fuel tubes that 
connect the carbs.  Hopefully you will just find that your fuel line is 
cracked since that would be the easiest repair.  But that also points to 
a bad petcock since you should not have fuel flow through the petcock 
when there is no vacuum present to the petcock unless it is in the Prime 

Hopefully this rambling makes sense to you and helps.  Good luck!


Drew Blanchard wrote:
> After a chilly start to the day, temps went into the upper 80s.  Looking
> forward to my ride home, I thumbed the starter and was rewarded with a very
> brief "thump" and some starter whine, but that was it.  Motor didn't turn
> over, and the starter seemed to be trying to move an immovable object.
> Fearing the worst but knowing everything had been fine on the ride into
> work, I pulled the tank and plugs to see if the motor would move without
> compression.  Yup.
> Note to self, remember to stuff rages very tightly over the spark plug
> openings.  Messy.  Very messy.
> When reassembled (and what a bitch it was reconnecting the fuel line) the
> motor initially made the same noise, then turned over with ease.  Obviously
> it was vapor locked.  I never had this issue on my '95, but that was also a
> stock set up.  Anyone else have this issue?  Is there a preventative measure
> I can take?
> Didn't get to ride the bike home, because somewhere, somehow I have a nasty
> fuel leak.  If I didn't know better, I'd say the leak was coming from the
> bottom of the motor.  And landing directly on the exhaust pipe.  I was very
> fortunate the motor never actually started.  Every time I turn the motor
> over I get a nice, steady drip, and I can't see where it's coming from.  I'd
> worked on the bike for several hours in the heat, and quit for the day.
> Fortunately, our maintenance guys at school let me put the bike in their
> garage for the night.  Once on the center stand, no leak.  Moving the bike
> or leaving on the side stand = leak.
> Grrr.....
> Drew in VT

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