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Vapor lock?

  • Thread starter Thread starter oblivionboyj
  • Start date Start date
O

oblivionboyj

Guest
I have an 80' GS550E.
I had the valves done a couple of weeks ago.
The engine starts fine when cold (with appropriate choke), and normally idles fine.
Today on the way to work I had to come to an abrupt stop and the engine died.
I couldn't get the bike restarted by either the starter of by "poping" it.
I waited like 20 minutes and I was able to pop it after that.
I would guess with a few more minutes of cooling down it would have started normally.
It had been sitting for an hour after I got to work and when I went back out to it, it started just fine.

I would swear I had vapor lock!
Is vapor lock a common problem with my bike, or am I missing an oft dicussed "normal" problem?
What is my fix to keep this from happening again?
 
If it happens again you can try removing the gas cap while listening for a vacuum sound. It could be the gas cap vent is plugged. Of course there are lots of other things it could be as well.
 
I am pretty sure it is not a hot ignighter.
It has an aftermarket electronic ignition.
I swear, it acts just like vapor lock.

Next time it happens I will try the gas cap.
 
These bikes don't vapor lock, the carbs don't get that hot

Does your petcock have a Prime position? Try riding it on Prime (along with popping the gas cap)
 
Nope, no prime.
Just reserve and full.

I will report back about the gas cap next time it happens.
I might just go ahead and replace the cap preemptively actually.
It is the original cap, or so I would guess.
The rubber is in good shape, but the cap is clearly old as dirt.
 
Big T said:
These bikes don't vapor lock, the carbs don't get that hot
Click to expand...
It's not so much a matter of carb heat. Vapor lock happens when fuel gets hot enough that it evaporates out of the pump, which is not capable of pumping vapor. Since our carbs are gravity-fed, it's hard to fool the 'pump'. :o

Big T said:
Does your petcock have a Prime position? Try riding it on Prime (along with popping the gas cap)
Click to expand...
oblivionboyj said:
Nope, no prime.
Just reserve and full.
Click to expand...
Check your petcock settings. I am under the impression that your two positions are RUN and PRIme. I don't think you have a REServe position. :-k

.
 
Steve said:
Check your petcock settings. I am under the impression that your two positions are RUN and PRIme. I don't think you have a REServe position. :-k

.
Click to expand...
I would have to look to be sure, but it doesn't matter.
The condition persists in either position.

EDIT-
Just went and looked...
The positions on the petcock are ON and RES

FWIW...
Gravity fed fuel systems can vapor lock too.
The pump is not what's fooled.
The carb needs liquid fuel to work properly.
I have personally been on scene for crash investigations where aircraft with a gravity fed fuel system had fuel starvation caused by vapor lock.
The pump is not what has a problem with fuel vapor, the carb does.
 
Last edited:
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