Fuel Question

[mattro51]

2002 Yamaha F80 Carburated

Engine seems to be starving for fuel. Thourghly cleaned and synched carbs which took care of the sneezing issue. Now my issue seems to be a poor fuel supply. I took four feet of clear hose and hooked it straight to the fuel filter on the engine. I ran the opposite end of the hose directly into the tank. No fittings inbetween. The fuel pump pulled gas the entire length of the hose with no air bubbles. I took an eight foot piece of same diameter clear hose simulating the length of entire fuel hose system which does include a fuel water separater and primer bulb. The fuel pump was not able to pull gas from the tank and maintain a full gas line. There was a large air bubble in the line. Is this normal? There is no leaks from the gas tank to the fuel filter. You guys were a great help on the carb. side by correcting my sneeze issue. The engine currently will idle great with the eight foot piece of hose but at high RPM the engine begins to run rough.

Thanks

[robert graham]

Could be an O-ring seal leak on the quick disconnect fitting on front of cowling?

[throrope]

Could be an O-ring seal leak on the quick disconnect fitting on front of cowling?

Another cheap and often last addressed repair - good suggestion.

[mattro51]

The hose has no quick connects. It is ran directly from the fuel supply to the fuel filter

[robert graham]

The hose has no quick connects. It is ran directly from the fuel supply to the fuel filter

Then where could the air bubble come from?.....

[99yam40]

Where is the primer bulb?

You need to use it to prime the system so the fuel pump can pump fuel, it does not suck and pump air very well.

You need to use a fuel pressure/vacuum gauge to see if pump is able to do its thing. the Vacuum side of pump will show if there is too much of a restriction going back to tank.

Maybe you have a fuel pump problem

[mattro51]

I attached the line to the fuel filter, filled the line with fuel, then placed the other end in the tank. This left approximately 2-3 inches of hose that had air in it. When I had the short line attached the fuel pump pulled the air out and filled the hose with fuel very quickly. When I attached the longer hose the pump would not pull the air out and only pulls a small trickle of fuel past the air bubble. It doesn't seem that a 48" increase in line length would increase the friction loss or negative pressure needed to a point above that of which a properly functioning fuel pump could overcome.

[throrope]

Quick question - when you connected the long hose, did you use the tank connector or put the hose directly in the fuel?

Since you're painfully loosing hair, I though I'd toss in another cheap past experience.

Years ago I had the cap vent closed, while running which collapsed the poly tank enough to jam the plastic pick-up tube against the bottom and broke it off. Over time, the plastic became brittle. A crack at the top of the tube within the tank will bypass air instead of allowing fuel to flow.

[mattro51]

I put the hose directly into the tank. I made sure to have a full tank of fuel and kept the hose off of the bottom of the tank.

[99yam40]

It doesn't seem that a 48" increase in line length would increase the friction loss or negative pressure needed to a point above that of which a properly functioning fuel pump could overcome.

Like I said before, maybe that is your problem