Last half of the tank issue - Kawasaki KLR 650 Forum
2008+ KLR650 Wrenching & Mod Questions For repair, maintaining or modifying discussions related to the newly updated 2008 and beyond, Generation 2 KLR650 Motorcycle.

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post #1 of 36 Old 03-27-2020, 07:03 PM Thread Starter
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Last half of the tank issue

Hey all. I've previously posted on the thread below as what I was experiencing was similar to the original thread post. Basically, I've got hesitation from mild to pretty bad under load. It feels like you are running out of fuel. It always seems to appear on the last half of the tank - never the first half. Today, with about 130 miles on the tank I went from a dead stop @ stop light, to pull a decent little hill on a hwy - so getting back up to 70 mph. By 3rd gear, I thought I was going to have to pull off the road. Keeping at it and finally getting up to 70, the power would kind of fade in and out.
I've recently did the KLX needle - same issue existed previously. I also have the manual fuel shut-off from EM.

I've rooted around, checking things like kinks in lines, vent line, fuel level in the bowl, etc. But I've never found the smoking gun on why this is occuring. When I did the KLX, I did have the carb apart and didn't see anything (at least that I know to look for).

https://www.klrforum.com/2008-klr650...ed-pump-4.html

Sounds like a lawnmower, Rides like a paint shaker!

I got 99 problems but fuel injection, 6th gear or a 2nd cylinder ain't 1!

My wife: "I didn't know if that was you coming home, or a neighbor mowing"
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post #2 of 36 Old 03-27-2020, 07:55 PM
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Try it with the fuel cap open. You may have stuck or sticky tank vents. They live in the cap.
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“On the way downtown I stopped at a bar and had a couple of double Scotches. They didn't do me any good. All they did was make me think of Silver-Wig, and I never saw her again.” -Philip Marlowe

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post #3 of 36 Old 03-27-2020, 10:29 PM Thread Starter
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I think I'll disassemble the cap. I've googled and have seen some pictures of what I'll call a small flapper valve that have torn on some.

Looking back on today's ride. It got to be an issue as soon as the sun came out and things heated up. Black bike exacerbates the issue. Thanks for the help. I'll be glad for this particular issue to be gone. Not a good feeling when you are in the middle of nowhere.

Sounds like a lawnmower, Rides like a paint shaker!

I got 99 problems but fuel injection, 6th gear or a 2nd cylinder ain't 1!

My wife: "I didn't know if that was you coming home, or a neighbor mowing"
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post #4 of 36 Old 03-28-2020, 02:26 PM Thread Starter
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Things seem to be working. Could it be that it just can't keep up with the volume of air needed to equalize, essentially putting it in a state of vacuum? I'm guessing there is a fine line between a vacuum state and too much head pressure at full tank.
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Sounds like a lawnmower, Rides like a paint shaker!

I got 99 problems but fuel injection, 6th gear or a 2nd cylinder ain't 1!

My wife: "I didn't know if that was you coming home, or a neighbor mowing"
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post #5 of 36 Old 03-28-2020, 02:34 PM
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Pul the pink plastic bits out and make sure the umbrella seals are free and clean. That's about all you can do, other than eliminating them.

Tom [email protected]

“On the way downtown I stopped at a bar and had a couple of double Scotches. They didn't do me any good. All they did was make me think of Silver-Wig, and I never saw her again.” -Philip Marlowe

“'Why' and 'How' are words so important they cannot be too often used.” -Napoleon Bonaparte

Sting like a butterfly.
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post #6 of 36 Old 03-28-2020, 02:41 PM Thread Starter
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Pulled the upper flap off to see how the lower one looks. Upper and lower depending on your point of reference. Anyhow, shot carb cleaner and then canned air (at a low pressure/volume) through air passage.
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Sounds like a lawnmower, Rides like a paint shaker!

I got 99 problems but fuel injection, 6th gear or a 2nd cylinder ain't 1!

My wife: "I didn't know if that was you coming home, or a neighbor mowing"
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post #7 of 36 Old 03-28-2020, 04:41 PM Thread Starter
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Quote:
Originally Posted by Tom Schmitz View Post
umbrella seals
I knew my 'flapper valves' weren't quite up to correct nomenclature!

I was sitting here thinking more on this. Please correct me if my thinking is incorrect. Seems like a black tank collecting heat would create more head pressure, while these umbrella seals are supposed to allow the tank to equalize with outside pressure to keep from a vacuum state. These two forces are in opposition, not in concert. These umbrella seals seem to only allow air in, not out. When things heat up, is pressure keeping these closed, not allowing correct function?

Sounds like a lawnmower, Rides like a paint shaker!

I got 99 problems but fuel injection, 6th gear or a 2nd cylinder ain't 1!

My wife: "I didn't know if that was you coming home, or a neighbor mowing"
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post #8 of 36 Old 03-28-2020, 06:36 PM
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Sportinh2o, Test its fuel flow / air flow. With open cap & closed cap.

Get yourself an empty 5 + gallon fuel can/jug/bucket. Connect 1/4" fuel hose to fuel tap. If automatic vacuum fuel valve, connect a 3/16" vacuum hose, squeeze a Visine bottle near flat & connect to vacuum hose. That tiny amount of continuous vacuum is all that is needed to open the fuel valve.

The fuel needs to flow at a rate of at least 3 gallon per hour or 6.4 ounces per minute or better for the full tank. That would more than feed the worst fuel mileage (35mpg) I've ever gotten in a head wind at full throttle.

Could measure it on a cool night & a Hot Sunny day. It is pretty common to hear those fuel cap vents 'sing' or maybe its 'whimper' to us on a hot day.

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post #9 of 36 Old 03-28-2020, 06:53 PM
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Quote:
Originally Posted by Sportinh2o View Post
...These umbrella seals seem to only allow air in, not out...
They pass air both ways. Air comes in to let the gas out and they let the air out to allow for expansion due to heat build-up. Sometimes they even whine and moan.

If you look at the pink plastic thing you'll note that it has a labyrinth passage and at each end of the passages is an umbrella seal. One passage lets air out, the other lets air in. The labyrinth makes it hard for gas to get out. If you take the plastic thing out and leave it out, the tank will breathe easier but gas will dribble out if you tip the thing over. The solution is 'don't tip the thing over'.

Tom [email protected]

“On the way downtown I stopped at a bar and had a couple of double Scotches. They didn't do me any good. All they did was make me think of Silver-Wig, and I never saw her again.” -Philip Marlowe

“'Why' and 'How' are words so important they cannot be too often used.” -Napoleon Bonaparte

Sting like a butterfly.
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post #10 of 36 Old 03-31-2020, 04:57 PM Thread Starter
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Quote:
Originally Posted by pdwestman View Post
Sportinh2o, Test its fuel flow / air flow. With open cap & closed cap.

Get yourself an empty 5 + gallon fuel can/jug/bucket. Connect 1/4" fuel hose to fuel tap. If automatic vacuum fuel valve, connect a 3/16" vacuum hose, squeeze a Visine bottle near flat & connect to vacuum hose. That tiny amount of continuous vacuum is all that is needed to open the fuel valve.

The fuel needs to flow at a rate of at least 3 gallon per hour or 6.4 ounces per minute or better for the full tank. That would more than feed the worst fuel mileage (35mpg) I've ever gotten in a head wind at full throttle.

Could measure it on a cool night & a Hot Sunny day. It is pretty common to hear those fuel cap vents 'sing' or maybe its 'whimper' to us on a hot day.
So I did a flow test today. Put the bike out in the sun, full tank of fuel, fuel cap closed. Excellent flow. The last bit of the tank did lower in flow/volume, but not to the degree that I think it would cause an issue. Of course, I have been inside the cap now, so disturbing the umbrella seals could have made an impact. I think the only way to see if there is still an issue is to ride this tank out.

If the issue persists, I'll pull the umbrella seals out.

Also @ pdwestman, I re-jetted the carb to the suggestion you made on another thread. Running KLX needle, 142 main, #40 and 2 turns out. My previous tank was on the 140 main and I was getting 41mpg, mixed riding. My ride today to top off fuel was the first since I installed the 142. Limited ride, but it seemed better. More responsive. I'll update after putting up some real miles.

Thanks!

Sounds like a lawnmower, Rides like a paint shaker!

I got 99 problems but fuel injection, 6th gear or a 2nd cylinder ain't 1!

My wife: "I didn't know if that was you coming home, or a neighbor mowing"
Sportinh2o is online now  
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