Vapor lock

[Jet86]

How do you know if you have vapor lock, what are signs symptoms and what causes it???

And how to fix it?

[tweeter55]

Years ago wen I was running a truck, it had 2 saddle tanks. I experienced vapor lock in the heat of the summer. One time I put regular unleaded in one tank and gasahol in the other. If I switched to gasohol, within 1-2 miles it would vapor lock. I haven't experienced vapor lock with my C-10 because I still run regular unleaded. It also gets better fuel mileage with regular unleaded also. Don't know what you're running through yours or if regular unleaded is even available for you. Just my $.02 worth.

[Summit670]

I experienced vapor lock on my concours a few years ago.  I had installed an inline fuel filter and in the process figured I'd make it easier to drain the fuel by making the fuel line longer.   I just tucked the excess in and didn't think about it.

Well, the excess fuel line was behind the cylinders and when it would get too warm the bike would die.  I left my house, got on interstate and would drive like 5 miles, then the bike would die.   After I sat a few minutes the bike would start so I went back home via side roads in case it would die again.   Once home I removed the fuel filter and got back on interstate.  I'm not kidding when I say it died within a 1/2 mile of where it did the first time. Went back home, removed the excess fuel line and it was fine after that.

Also, last summer, was going west on I80, about 95 degrees out, and running about 80 against an estimated 15-20mph headwind, bike fully loaded for camping in the mtns, and the while passing a semi in eastern CO, the bike dies.  After 5 minutes of mental troubleshooting, I looked at the clear fuel line and noticed it looked empty so I turned the petcock to prime and saw it fill.   I figure the vacuum line going to petcock got so warm it collapsed on itself and shut off the fuel.  Once I got going I tried returned the petcock to "on" and it died again, then hit prime while still moving and it ran fine.   Left in in prime mode the next few days.  On return trip I switched to "on" and it has run fine ever since.   I'm going to replace the aftermarked vac hose with something a little more ridgid.

[George R. Young]

There's another similar phenomenon where fuel flow stops because the tank is not venting properly. Easy to check, just leave the gas cap open while riding.

[Jet86]

I don't know about type of gas but other then that the reply's are exactly what i was expecting to hear.

yesterday i'm pretty sure my bike vapor locked, i had just filled up the tank and was riding in a town about 12 miles from home and it was hot about 85, its starting to warm up here in cali, bike was running fine in town and then i hit the hiway on-ramp and the moment i hit the throttle it bogged down and tried to die, i let off of gas and hit it again and it wanted to just die so i had no choice but to pull over right there half-way down the on-ramp, the bike died and i waited about 1min and hit start button and it started right up and would idle fine but would die soon as i gave it any gas.

So i had this exact same problem about three years ago in hot weather and had to pay $110 for a flatbed tow, i had an idea what the problem was but did not no how to fix it and did not have the proper tools with me at the time.

Well this time i fixed it myself, i carry a small tool box with basic tools just for this type and other basic types of road side repairs.

At first i wasn't sure what the problem was because the bike has been running like the King of the Road for two years with no problems, So i stand back a few minutes and look at her thinking it died the moment i gave it gas witch rings a bell and gave me flashbacks to three years ago and leads me to think fuel starved / crap in float bowl, vapor lock, plugged fuel filter, gas cap, kinked/collapsed fuel line from heat.

First thing i did was break out my tools and grab the foot long hose and drained all 4 carb bowls and while i was there i seen that the clear fuel line was crimped/kinked about half inch from the fuel filter and the line was only half full, so play around with the line trying to straighten it out by moving it around then one at a time one i open the carb screw and turn petcock to prime til i see good gas flow from the hose to ground, (careful here don't want any fires).

Second i open the gas cap and start it up then hit the gas and all was good.
i drove home with the gas cap loose, not wide open for bugs to dive bomb, when i got within a block from home i locked the gas cap.

about 30min later i needed to run an Arron a few miles away and i had no problem but i expect this could creep back up on again with temps getting hotter now.

MY CONCLUSION:

I think this is very important, three years ago when this happened it was hot outside and i had just filled up the tank and drove 12 miles to a Lows store, after about 30min when i came back to my bike it started but would die when i gave it any gas.

yesterday i had just filled up my tank and drove 12 miles and it was hot outside, sound familiar.
i think the cause of the problem is a full tank of gas adds pressure and with heat and pressure on the fuel line it kinks/collapses - Instant Vapor Lock.

Now in my situation it could have been a combination of things but from now on i will not top off the tank in summer or anything over 72-75f

What i gotta do now is run out that tank of gas and remove the tank and check all the lines witch i know all should be good except maybe the one that kinked and unfortunately that's the main fuel line that plugs in between the carbs. little bit of a pain to swap but the line is probably still good just needs re-routing but again unfortunately i will probably need longer line if i want to re-rout.

the line i have is the clear tygon about 2 year old, i have heard that tygon does kink kind of easy with a little heat but the good side is it dont flak off little bits and plug up filter and carbs.

i still would like to hear more on this, draining the carb bowls would have been much easyer if i had a 4to1 hose system or maybe even steve's drain tubes would stop vapor lock?

 

[turbojoe78]

Steve's overflow tubes won't stop vapor lock, but they will stop hydrolock.

I don't think your having a vapor lock issue, I think your having a fuel starvation issue.

My guess is the problem is with your fuel line kinking and limiting the flow of gas to the carbs.

Your fuel line should run from the petcock, over the #1 and #2 carbs and down between the #2 and #3 carb.
It should only be long enough to just make it over the #2 and then down, if it's a little too long, that's when it can kink.

[Nosmo]

I agree with turbojoe78, I don't think your real problem is vapor lock, but it might be contributing.

Vapor lock happens when the fuel in a line gets so hot that it boils and forms vapor.  The pressure of the vapor pushes back against the gravity pressure trying to bring fuel down from the tank, and keeps the fuel from flowing through the line into the carbs.  The problem can be made worse by the kink in the fuel line and/or the filter, which act as restrictions.

Draining the carb bowls might have had a therapeutic effect, simply by allowing cooler liquid fuel to drain more easily downward into the supply line and carbs, but it is a temporary fix at best.

Removing all line kinks, as many bends as possible and eliminating the filter or getting one with less restriction might help.  Try to have your fuel line go as vertical as possible, without horizontal sections.  Long horizontal sections give the fuel more area to absorb heat.

Opening the cap will cure the supply problem if you have a faulty tank vent, and the tank gets a slight vacuum in it as the fuel drains out.  That condition can also help to keep fuel from draining out of the tank, and add to the vapor lock issue.  Make sure your tank vents are working properly.

You could try putting some kind of insulating material between your engine and the fuel line.

http://en.wikipedia.org/wiki/Vapor_lock

[Two Skies]

Another thing that has been mentioned before is the charcoal cannister.  Sometimes, when you completely fill the tank, and then the fuel warms up (expands), fuel works it's way into the charcoal cannister/box thingie, which gets blocked in the process.

The last time I had bike running screwiness, I messed with this a bit, by blowing air into the cannister (disconnect cannister hose from tank, blow into hose, replace).  Dunno if that was the problem, but I got her running smooth again after that.

Since that time, I've made it a point to never fill the tank completely up unless I knew I was going to be running it down almost immediately (putting a lot of miles on the bike).  These days, that's easier as I pay cash for fuel, and most pumps are now prepay so I have to guesstimate how much the bike will take, and generally come out a little short.

I think the charcoal cannister/box thingie is a Cali-only option, but I'm not sure.  Mine has one, and I have a Cali bike.

[Jet86]

All good information -  and i do think the kink in the line caused most of my troble because it was a hot day and if im sitting in traffic my bike runs almost to the red line befor the fan comes on, i want to put a toggle switch to run the fan in town, i probably need a new thermostat to but thats another story and another time.

[SteveJ.]

An FYI on replacing the fan switch, if you leave the cap on, on a cold engine, you can replace the switch without draining the coolant. Just be quick, like a bunny. Now iff'n it's been two years, or close to it, since the coolant was changed, you might just as well do it right and replace the coolant. BTW, how old are the hoses? Five to six years is about max for reliable dependability on them.

[Jet86]

I changed coolant 4 years ago and i already bought a new jug of coolant 50-50
Hoses i have never changed so they are more than 5 years old and possible they have never been changed, however when i changed the coolant 4 years ago it looked very clean green.
i have a new jug of coolant but hoses will have to wait, not even sure i can aford a new fan switch.

[Summit670]

A way to help prevent fuel line kinking is to go to the local hardware store and buy a spring, then route the hose thru the spring, placing the spring at the point where the hose makes a sharp turn.

[T Cro ®]

The only time my bike has ever suffered a fuel flow problem with a right angle fuel filter is when I installed it and had just an 1" too much length in the fuel line..... It don't take much to kink the hose and fowl up your interstate warp speed engine....

[Gottaride]

I'd guess fuel line kinkage too. My Cali bike has the Napa 3006 fuel filter which is huge and has the 90 degree outlet. It lies directly on top of and is supported by the #2 carb. A section of transparent Tygon runs vertically to the carb intake port and is as short as possible. The whole fuel line assembly from petcock to carbs is as short and straight as could be managed. Immediated down stream of the petcock is an in line manual fuel valve straight in straight out. Immediately downstream of that is a 5/16" brass 90 elbow that redirects the fuel line toward the ideal fuel filter location. All fuel lines are standard heavy wall 5/16 ID black with tje exception of the final vertical piece of Tygon as mentioned.
No fuel starvation issues with full tank fuel temps well above 100F. My cali tank has the original three engine heat insulation pads with aluminum HVAC tape as a protective cover.
So many members have written about fuel line kinkage and starvation that I really took my time in trying to avoid the same pitfalls. So far so good. Good luck.

[Jet86]

I added new napa black fuel line to petcock and shortened it half inch then replaced the inline filter with a shorter one and that made it overall about an inch shorter and so far no problems, i also put in a toggle switch for the fan to keep the heat down when im in town sitting at red lights.

I was gonna replace the main fuel line from the carb but chickened out last minute, i got very lucky or unlucky last time and it took me about 6 hours to get the new line on, alot of walking around trying to find out where to hold my tongue and ended up biting my lip, someone on this forum said you gotta find the right spot to hold your tongue. 

[T Cro ®]

i got very lucky or unlucky last time and it took me about 6 hours to get the new line on, alot of walking around trying to find out where to hold my tongue and ended up biting my lip, someone on this forum said you gotta find the right spot to hold your tongue. 

One of the reasons I have a pair of right angle needle nose pliers is to help manipulate the hose connecting to the carbs...

One of the bigger mistakes I've seen made is to run the hose down from the carbs before looping back up to the tank. While it is easy to hook up one must now overcome the forces of gravity to some extent and this may help cause fuel starvation issues.

[Jet86]

One of the reasons I have a pair of right angle needle nose pliers is to help manipulate the hose connecting to the carbs...

One of the bigger mistakes I've seen made is to run the hose down from the carbs before looping back up to the tank. While it is easy to hook up one must now overcome the forces of gravity to some extent and this may help cause fuel starvation issues.

my little pea brain did not fully understand what you said. 

[T Cro ®]

my little pea brain did not fully understand what you said. 

Shortest most direct route from nipple to nipple...

[Jet86]

ok thats how i have it now, main carb line coming stright up from the nipple and curving over to my fuel filter and onto the petcock,, was you by any chance saying that some people have connected the hose from the bottom of the carb by turning the nipple down and connecting the hose? i seen that the nipple does move but i dont know how far but i made sure it was upright and that was one of things that made it hard to hook up because the hose would keep moving the nipple around when i trying to connect the hose.

[T Cro ®]

... was you by any chance saying that some people have connected the hose from the bottom of the carb by turning the nipple down and connecting the hose?

Yes...