Motorcycle Fuel System Question?

Question

In the process of trying to figure out what's wrong with my bike I've installed 2 inline filters for each fuel line out of the petcock. They are the clear kind so I can see what's going one. Here's the deal. The front filter never fills more than a few mms while the rear one fills right up to the top and stays that way. The bike runs great for the first 5 minutes then it just loses power, almost like when a plug goes bad. I'll let her sit for a while then take her out a few hours later and same thing. I'm wondering if the symptom of the filters is a hint to something that's going on and also, most importantly...

WHICH fiilter is behaving normally? Should it be filling up right away and staying that way even when the bike is off or should it always be almost empty like the other one?

BTW, I swapped the filters just to make sure it wasn't a bad one but they just did the same thing again.

*** New Test - I swapped the 2 lines, with each filter still attached , turned on the bike and watched as the full filter (now in front) slowly drained, while the empty filter (now in back) started to fill. Hmmm???

1990 Kawasaki Vulcan 750

Answer 1

Always give year, make, engine size and model # when asking questions. We need all of that info to give an informed answer.
I don't know how your petcock works, or how it's supposed to behave without that info.
Check that the petcock isn't restricted.
Turn the petcock off, remove both lines.
Put a container under the outlets and turn on the petcock to see if fuel flows equally from both.
Next, install the hoses with filters attached, onto the petcock.
Remove the hoses from the carbs and repeat that test to make sure the filters aren't restricting fuel flow.
Depending on what bike you have, the overflow tubes on the float bowls are also the vent tubes.
If one of the vents were clogged, fuel wouldn't enter that float bowl at the normal rate.
Try blowing through the tubes to check for blockage.
The gas cap vent may be clogged.
While one line is letting fuel escape from the tank, the other line is acting as the vent.
The negative pressure from the fuel tank is sucking on the second line, preventing it from flowing.
Try removing the gas cap to see if the fuel flows normally.

Answer 2

I would pull the fuel line with the partially filled filter and replace it making sure it was the same diameter as the line that appears to be working correctly. You could also open the petcock with the line off to check if fuel can flow freely out of the tank (don't do this when the motor is hot and try to contain the fuel leaving the tank).

If the line is ok and gas easily comes out of the tank, drain the tank and pull the petcock. They are cheap to replace and you can also remove any sediment or rust that may have formed inside the tank. The screen filter should also be replaced at this time.

Answer 3

The filter should fill with the petcock in the on position. You may have a clogged petcock or, there is also a screen on the petcock inside the tank. That may be clogged.
And yes, it sounds like it's starving for gas when you run it.
I'm assuming here that you have two petcocks.
Is it a single tank or split tanks?

Answer 4

You've got restricted fuel flow.
Two filters in each line?
One doesn't fill? That alone might be the restriction.
As the bike draws fuel, float bowl levels drop.
Finally it starves.
If you had a problem origionally, check for a
clogged tank vent. It can cause this problem.
Did you change the fuel lines.
Did you use the same size hose?
Also check for any damage to the inside of the fuel lines at all those connections. That can do it.

Answer 5

I can only say that my husband has owned many motorcycles (both carborated and fuel injected) and now that he is looking for yet ANOTHER motorcycle, he does NOT want carborated.... He prefers fuel injected 100% so there's got to be a good reason!

Answer 6

ha ha, you said petcock.