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Discussion Starter #1
My 1994 KLR is having this phantom problem the mechanic can't seem to fix after three visits. Afer riding 20 minutes it will start stuttering a little and lagging and surging between 3800 an 4700 RPM, just not holding steady.



Then sometimes this progresses to complete bucking with the throttle full open just trying to keep going and it won't go over 51 mph. If I try to advance the throttle rapidly in any gear it just completely bogs down.



So after getting up the hill I tyrn off my bike and the gas cap vent is hissing loudly. I open it and there is a whoosh. Look in the gas tank and my gas is in a full rolling boil. It continues to boil for 4 minutes. I check at the next stop and it is doing the same thing, this is at altitude.



It seems (the bogging down) to sometimes occur about 20 minutes riding after getting fuel. The thought I have is that my fuel cap vent isn't working. And that when I fill up with fuel that comes from underground tanks that are probably65 degrees it takes about 20 minutes to come to bike temperature and then since my fuel vent isn't working it is pressurizing my tank.......



My bike might be running to hot too, it is running between 188 and 220 Fahrenheit. What should the range of operating temperature be?



Anyone have this problem and solved it? Or anyone with any hypotheses?
 

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Sounds to me that the fuel tank vent is plugged like you mention. Anything will boil at a lower temp if it's under vacuum.

Check the fuel tank vent under the cap.
 

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Discussion Starter #3
vent plug??

Sounds to me that the fuel tank vent is plugged like you mention. Anything will boil at a lower temp if it's under vacuum.

Check the fuel tank vent under the cap.
The thing is that once when I was having the problem I opened the fuel tank cap and rode with it open and it didn't start running right.

It seems that my fuel is hot(is my bike running too hot) and it is vaporlocking so I removed my inline fuel filter and put in heavy duty fuel line from the tank to carb. This helped a little.

Another question, the fuel line is still super hot next to the engine, Why is my bike holding on to so much heat?
 

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Gasoline will boil and the higher the altitude the easier it boils. The pressure in the tank, held by the cap will help keep it from boiling. You might want to figure out why it is running hot as that may be or contribute to the problem.
 

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Discussion Starter #5
What is too hot????

What is normal 1st gen temperature range?

Boiling occurred at 199-203F engine coolant temperature.

And I wasn't in a vacuum trailing a stealth bomber at 72,000 feet. This was 8000-10000 feet.

I think we can say without a doubt fuel tank temperature was too hot; why though?
 

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The tank vent system is designed to allow air into the tank as fuel flows from the tank into the carb and is burned. There should be neither positive pressure nor vacuum in the tank. If you find either, the tank vent system is not working correctly. If the tank vent is not clear it won't allow air into the tank creating a vacuum inside. The fuel wont be able to flow out of the tank causing a fuel starvation issue for the engine.
The tube you found at the lower rear of the tank should have a hose on it leading down behind the engine and terminating as an open end. It should not be plugged. If there is no hose it should still NOT be plugged. That tube continues upward inside the tank and connects to the fuel cap at the flange the cap seats against when closed. You can carefully blow air through this tube when the cap is open. The passage continues through the cap into the tank. DO NOT use compressed air to check the flow through the cap. I have not seen it yet but I understand there is a rubber one way valve inside that can get damaged if subjected to compressed air. Here is a link to the procedure for repairing the cap if plugged. It is on KLR650.net forums and is an excellent write up on the fuel cap assembly repair.
http://www.klr650.net/forums/showthread.php?t=101547&highlight=tank+vent+seal
I recently found a small screen filter inside the plastic fitting the fuel line connects to on the carb. You may want to pull off the fuel line and check this screen filter for debris. It could be partially plugged also causing fuel starvation. This was on my 2011, not sure if it exists on a 1994.

EDIT: Sorry that little screen filter doesn't seem to show up on the parts list till 2010. jj

Hope this helps.....justjeff
 

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Discussion Starter #7
Good news/bad news

The rear tank vent and cap vent seem to be working properly. I can blow air through the tube up through the cap vent pretty freely.
 

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To me it sounds like you have winter version gasoline. The gasoline will start to boil at a lower temp. Than a summer version of gasoline. Some winter version will boil at temps as low as 90 degrees.
 

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Has your mechanic checked to see if the water pump is working properly? Maybe its not circulating water/anti-freeze?
 

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The rear tank vent and cap vent seem to be working properly. I can blow air through the tube up through the cap vent pretty freely.
troutbum33,
With the fuel cap OPEN, connect a piece of fuel line to the TAPERED NIPPLE air vent, then blow with your mouth.
Chances are that there is NO LONGER any SEAL between the nipple and the metal vent pipe IN THE TANK. And you were just blowing AROUND the nipple.

pdwestman
 

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You are having a venting problem. Thinking back to chemistry class, a cylinder of water under enough vacuum will boil at room temp. That is what is happening in your gas tank, under enough vacuum the boiling point of the gasoline is dropping enough to boil at air temperature. Somehow a vacuum is being formed, which is starving your engine of fuel, and boiling your gas. That big whoosh is air rushing in. Gas does not boil at 90F, it will evaporate, but not boil, think gas can in the sun when it is 105F, even winter blends don't boil.
 

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What I am saying is Winter formula Gasoline has alot of very cheap butane in it. The same stuff that is in lighter. how much is up to the refiner. there is no set amount in The Feds have set for winter formula Gasoline. But there is set amount for Summer blend and it can not contain more than 2 percent in it. But then there is state regs. But over all there is is 23 gasoline formula the refiners
Use but each refiner has its on formula type tweaks.
 
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