Fuel starve at load, air in fuel line, tank vacum? - Kawasaki KLR 650 Forum
1987 to 2007 Wrenching & Mods For maintaining, repair or modifications of Generation 1 KLR's. 2007 and earlier.

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post #1 of 12 Old 08-20-2012, 12:40 PM Thread Starter
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Fuel starve at load, air in fuel line, tank vacum?

1994 KLR 650

It is absolutely a fuel starve problem, air in the fuel line between tank petcock and Carb.
In regard to my cutting out problem it turned out to be air getting in my fuel line between the petcock and outlet of fuel filter. Happened bad going up a steep grade at 65. I looked and could see air in the line after the filter. So I pushed the tube tightly onto tithe fuel tank petcock and the fuel filter and taped them both.

Then I remembered someone saying something about a vacuum in the fuel tank. So I popped the tank lid to take care of that if it was a problem. Off I go for 375 miles of major rough riding and probably 20,000+ feet in vertical gain and drop. No problems.
Then I get back to that same hill and halfway up it starts cutting out and valves clattering, unbelievable! So I get down there and look and there is air in the fuel line again. Both connections still taped.

So to test the vacuum theory I pull the fuel line off the petcock at the tank Nothing! Shouldn't fuel be flowing freely out of the tank at this point?

Somebody mentioned a possible issue with a butterfly valve in the petcock that gets messed up, anyone heard of this?

So if I do have a vacuum in my tank where are the vents I need to clear out?

Last edited by troutbum33; 08-20-2012 at 12:44 PM.
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post #2 of 12 Old 08-20-2012, 01:11 PM
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The petcock itself is vacuum operated. There is an air line running from the petcock to the carb. Not flowing when the motor is off is normal with the stock petcock because there is no vacuum to open it. I heard of problems with the stock set up so I replaced mine with a manual petcock from Eagle Mike.

http://eaglemike.com/Manual-Petcock-for-KLR650-mpcy.htm

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post #3 of 12 Old 08-20-2012, 01:13 PM
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Originally Posted by troutbum33 View Post
So to test the vacuum theory I pull the fuel line off the petcock at the tank Nothing! Shouldn't fuel be flowing freely out of the tank at this point?

Somebody mentioned a possible issue with a butterfly valve in the petcock that gets messed up, anyone heard of this?
No fuel will flow from an operational factory stock petcock, unless the engine is running, pulling vacuum on the petcock . . .

No "butterfly valve" in the petcock, AFAIK; however . . . a diaphragm resides there. The diaphragm responds to the vacuum in the tube connected to the carburetor vacuum port, opening a valve allowing fuel to flow.

Given the garvity-fed fuel system, I can't account for air in your fuel line.

Maybe other forum members have experienced the phenomenon.

Even with air in the fuel line, seems to me like the float bowl would harbor enough liquid fuel to feed the jets, enabling the engine to run. When drained, the float bowl has nothing but air inside; gasoline from the fuel line fills the bowl when the petcock is actuated by carburetor vacuum. Since the whole fuel bowl volume of air can be displaced by fuel flow, some air in the fuel line shouldn't be a serious problem, I'd think. Don't know; clarifications and corrections welcomed!

Last edited by LoneRider; 08-20-2012 at 01:19 PM.
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post #4 of 12 Old 08-20-2012, 02:05 PM
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Quote:
Originally Posted by troutbum33 View Post
1994 KLR 650

It is absolutely a fuel starve problem, air in the fuel line between tank petcock and Carb.
In regard to my cutting out problem it turned out to be air getting in my fuel line between the petcock and outlet of fuel filter. Happened bad going up a steep grade at 65. I looked and could see air in the line after the filter. So I pushed the tube tightly onto tithe fuel tank petcock and the fuel filter and taped them both.

Then I remembered someone saying something about a vacuum in the fuel tank. So I popped the tank lid to take care of that if it was a problem. Off I go for 375 miles of major rough riding and probably 20,000+ feet in vertical gain and drop. No problems.
Then I get back to that same hill and halfway up it starts cutting out and valves clattering, unbelievable! So I get down there and look and there is air in the fuel line again. Both connections still taped.

So to test the vacuum theory I pull the fuel line off the petcock at the tank Nothing! Shouldn't fuel be flowing freely out of the tank at this point?

Somebody mentioned a possible issue with a butterfly valve in the petcock that gets messed up, anyone heard of this?

So if I do have a vacuum in my tank where are the vents I need to clear out?


Ditch the fuel filter.

No eye has seen, no ear has heard, no mind has conceived what God has prepared for those who love him. 1 Cor 2:9
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post #5 of 12 Old 08-20-2012, 04:23 PM Thread Starter
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You mean replace the fuel filter right?
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post #6 of 12 Old 08-20-2012, 05:04 PM
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You mean replace the fuel filter right?

No get rid of it, just a straight piece of fuel line from the petcock to the carb. Try it see what happens.

No eye has seen, no ear has heard, no mind has conceived what God has prepared for those who love him. 1 Cor 2:9
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post #7 of 12 Old 08-20-2012, 05:05 PM
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Originally Posted by troutbum33 View Post
You mean replace the fuel filter right?
I think he means take it out. Merely a troubleshooting step.

I've had issues with in line fuel filters before.

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post #8 of 12 Old 08-20-2012, 06:48 PM
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KLR's have internal tank filters, or screens . . . jettisoning the in-line fuel filter doesn't mean no protection at all. However, should the petcock internals deteriorate and fragment, a functional in-line filter can protect the carb from this type of debris.

As a test of the filter's flowability, you could disconnect the fuel line at the carburetor, place the end in a clear container, then start the engine; see if fuel flows freely . . . this test may also determine whether the vacuum-actuated petcock is functioning properly . . .
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post #9 of 12 Old 08-20-2012, 08:34 PM
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Get rid of the Cal emissions, that stuff doesn't allow the tank to vent correctly. I had similar symptoms and on a whim decided to pull the smog crap. My bike has never run better. My bike's tank was under vacuum and fuel would not flow. Also I still have the vacuum petcock with no problems.

1) You will need to to either plug the tee off vacuum line that goes to the smog crap or just run run a new piece of vacuum line from carb to petcock.

2) Tape hole left in air box. I used gorilla tape.

3) Plug right side tank vent. (remove seat to find on lower rear).

4) From left side tank vent (remove seat to find on lower rear) run vent line to under side of bike).
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post #10 of 12 Old 08-20-2012, 09:26 PM
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Originally Posted by CraigES View Post
Get rid of the Cal emissions, that stuff doesn't allow the tank to vent correctly. I had similar symptoms and on a whim decided to pull the smog crap. My bike has never run better. My bike's tank was under vacuum and fuel would not flow. Also I still have the vacuum petcock with no problems.

1) You will need to to either plug the tee off vacuum line that goes to the smog crap or just run run a new piece of vacuum line from carb to petcock.

2) Tape hole left in air box. I used gorilla tape.

3) Plug right side tank vent. (remove seat to find on lower rear).

4) From left side tank vent (remove seat to find on lower rear) run vent line to under side of bike).

My bike runs fine with all the smog stuff still hooked up.

No eye has seen, no ear has heard, no mind has conceived what God has prepared for those who love him. 1 Cor 2:9
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