Negative pressure in fuel line?
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5th Gear
Joined: Sep 2010
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Negative pressure in fuel line?
Just got back from a 5,000+ mile trip on my 1998 Electra Glide Classic. Over 10 times during the trip the bike would sputter and then die. I would coast over to the shoulder and by the time I got there the bike would restart no problem. Here are the circumstances. 1. Only happened when tank was under half full. 2. Only happened when outside temperature was over 95 degrees. 3. Only happened when traveling at 60 mph or more. If any one of these three were not the case the bike ran fine. Additional information, bike has 97,000 miles on it and it has a carburetor. Any suggestions what I should look for to solve this problem? Thanks
Intermediate
Joined: May 2017
Posts: 35
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From: Rincon, GA
Sure sounds like a fuel delivery problem but it could be something else. Start simple. If you still have the vacuum operated fuel valve (petcock) installed on that bike then check your vacuum line on the back of the fuel valve. Trace it back to its connection on the intake and make sure the line is in good shape and is not plugged or collapsing under normal vacuum pressure. You can disconnect it and run the bike for a quick sec (until the carb bowl empties itself) to make sure you are getting a negative pressure at the fuel valve. You should be able to tell by putting your finger on the end of the line, the vacuum should hold the line on your finger. If this is good, I would recommend disconnecting the fuel line from the fuel valve, turning the fuel valve to the normal position and apply a vacuum pressure to the back of the fuel valve. Make sure you have a cup under the fuel valve to catch the fuel. When vacuum is applied to the diaphragm of the fuel valve fuel should flow freely through the petcock. If this appears to be ok, then you may just have a slightly clogged in tank filter that is allowing fuel to get by under full tank, or light engine load conditions, but when the fuel tank gets low or high load engine conditions exist the filter may not be allowing enough fuel to flow to the carb.
Seasoned HDF Member
Joined: Feb 2007
Posts: 6,085
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From:
You state : 1998 Electra Glide Classic
Is that a fuel injected version?
If fuel injected: There is a piece of fuel tank liner that sometimes separates right at the bottom center of fuel tank, directly below the access door.
The piece will be about the size of a USA quarter and it gets sucked towards the fuel filter sock and blocks fuel.
When you pull over or shut down (no suction) the piece floats away to later repeat again and leave you rather confused.
Solution:
Remove top access panel
Look with flashlight for liner piece
Drain fuel, wipe inside of tank, filter fuel, return fuel to tank.
This is a simple do it yourself.
If you take it to a dealer they will make it extra complicated.
Is that a fuel injected version?
If fuel injected: There is a piece of fuel tank liner that sometimes separates right at the bottom center of fuel tank, directly below the access door.
The piece will be about the size of a USA quarter and it gets sucked towards the fuel filter sock and blocks fuel.
When you pull over or shut down (no suction) the piece floats away to later repeat again and leave you rather confused.
Solution:
Remove top access panel
Look with flashlight for liner piece
Drain fuel, wipe inside of tank, filter fuel, return fuel to tank.
This is a simple do it yourself.
If you take it to a dealer they will make it extra complicated.
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,071
Likes: 1,006
check for restricted fuel flow or float level height. with the extra head from a full tank, it is keeping up but as head pressure drops flow isn't enough. if the tank isn't venting it would be reasonable to conclude the problem is not level related. as was brought out, if petcock is vac sourced make sure no leaks of soft/pinched hose.
look at fuel hose routing for a possibility of heat soak and boiling fuel in the line.
look at fuel hose routing for a possibility of heat soak and boiling fuel in the line.
Grand HDF Member
Joined: Apr 2007
Posts: 3,726
Likes: 3,071
From: Brighton, MI
See post #11 in link below, it will eliminate on potential cause:
https://www.hdforums.com/forum/evo-c...l-valve-2.html
I agree with the previous replies, check your float needle and venting. YD
https://www.hdforums.com/forum/evo-c...l-valve-2.html
I agree with the previous replies, check your float needle and venting. YD
Seasoned HDF Member
Joined: Feb 2007
Posts: 6,085
Likes: 1,128
From:
This is a link for a parts finder.
The link helps to identify exact parts and discuss items replaced.
http://partsfinder.onlinemicrofiche.....asp?make=hdmc
The link helps to identify exact parts and discuss items replaced.
http://partsfinder.onlinemicrofiche.....asp?make=hdmc
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