Fuel from overflow

[TracyPrier]

Hi all.

 

Hoping knowledgable heads here can help point me in the right direction.

 

My bike is a 2000 RT-P that I did a canisterectomy to about 8 months ago. I've noticed over the last week or so that fuel is running out of the overflow pipe onto the ground.

 

Well actually I can't tell if it's the overflow or vent as they are both together and disappear up into the bike.

 

When I finished a ride yesterday I placed a container under the hoses. The bike is parked on it's centre stand on level ground. This morning there was a good 50 mls of fuel in the container.

 

I noticed too that when I reverse out of the garage onto our downward-sloping driveway that it dumped a further 50 ml or so.

 

Could this be a blocked vent causing the tank to pressurise?

 

Anyone ever come across this before?

 

Thanks

Tracy

[bmwmick]

Easy to check for a blocked vent, open the cap slightly.

 

You may also have a bad vent hose inside the tank. The rain vent and the vapor vent both pass through the fuel. If either of them have cracks, they can allow fuel to dribble out the vent hoses.

 

Mick

[smiller]

One possibility is as Mick mentioned, any leak at either hose where they connect to the fuel filter plate inside the tank will cause seepage. Another possibility is that fuel is simply being forced out of the vent line as it expands due to heat. If this is the case you can fix by inserting a one-way vacuum check valve (should be available at any auto parts store) in the vent line so that air can be drawn into the tank but fumes/fuel will not be able to exit.

 

BTW an easy way to figure out which hose is which is to just send some compressed air (or even some water) into the drain opening (the small hole in the fuel filler area) and observe which hose it exits from on the bottom.

[Green RT]

BTW an easy way to figure out which hose is which is to just send some compressed air (or even some water) into the drain opening (the small hole in the fuel filler area) and observe which hose it exits from on the bottom.

 

If there is a possibility that the vent hose may have cracks inside the tank, it probably isn't a great idea to run water through it, though the liklihood of much leaking into the tank seems small.

[Rob L]

If you overfill the tank (all the way to the top)and park it, fuel WILL expand and leak from the tank VENT hose. This has happened to my bike several times since the canisterectomy. If you notice fuel leaking when the tank is full, loosen the fuel fill cap and it will stop! Do not fill the tank to the top unless you plan to ride!

[TracyPrier]

Hi guys

 

WOW! you guys know lot's a stuff

 

Gently blew air up both hoses and cleared them but this morning there was still gas in the container SO it's looking like the vent hose is cracked... sigh. No the tank is not over filled and it is now winter here so doubt it is heat causing expansion either.

 

Figure I might as well do the filter while it's all apart.

 

I've downloaded Rob Lentini's instructions on fitting an external filter. Do you guys think it is worth doing this?

 

Can you guys confirm that I need 5/16 (8mm) high pressure fuel hose? how much do you think I should buy to replace the vent hoses and do the external filter (if it's recommended)?

 

Thanks again for the advise... have been really scratching my head about this one.

[Ken H.]

external filter. Do you guys think it is worth doing this?

 

Can you guys confirm that I need 5/16 (8mm) high pressure fuel hose? how much do you think I should buy to replace the vent hoses and do the external filter (if it's recommended)?

I've kind of come full circle on the external fuel mod. Given that all modern cages have them in the tank too, and how few real clogging issues there are, I say leave it. Heck, on the new hexheads it's not replaceable as a service item at all.

 

But if you do want to do it, kind of depends on where you put it. If back by the rear shock pre-load adjuster as many do, figure about 4 ft.

 

BTW the vent hose is not 5/16" fuel injection hose. Just regular old 1/4".

[DavidEBSmith]

My understanding is that the fuel pump injection on the hexheads only pumps as much fuel as the bike needs, in contrast to the setup on the oilheads that pumps a lot a fuel and returns the excess to the tank. So the idea is that the hexhead is circulating less fuel through the filter and so the life is longer.

 

Whether you need to do the external fuel filter mod probably depends on where you ride. If you stick to main highways, your chance of getting bad gas is less. If you're out in remote areas where the stations may not sell a lot of premium and may not be in a hurry to replace those expensive fuel line filters, you have more of a chance of having a problem. Fuel filter problems are rare, but if you have one clog, you'll be kicking yourself for not doing the mod.

 

If you carried a spare filter and the o-ring for the fuel pump plate, you could almost change the filter by the side of the road, and would have about 75% of the protection from Murphy's Law than you would have doing the external fuel filter mod. (Maybe 80%, factoring in the possibility of doing the mod wrong.)

[Stan Walker]

So the idea is that the hexhead is circulating less fuel through the filter and so the life is longer.

 

Kinda shaky logic in my opinion.

 

It would seem to me that it's not the amount of fuel circulated that matters but the amount of dirt introduced into the tank (assuming it all gets captured). And that would be the same in either case.

 

Stan

[TracyPrier]

Hmmmm... interesting. Over here in New Zealand we don't really have too much issue with questionable fuel supply and my riding IS on sealed roads (hey she's an RT, not a GS )

 

I had originally thought to just replace the standard filter when doing the vent hoses. I bought the bike from Long Beach BMW and I'm pretty sure they didn't do the filter so who knows what state it's in... and as it IS a fairly invloved process to get to...

 

I hadn't thought about the potential risks of mounting one externally, which does stand to reason of course. Has anyone who has done one of these mods ever had any problems??

 

Thanks again for the shared wisdom guys

[TracyPrier]

BTW the vent hose is not 5/16" fuel injection hose. Just regular old 1/4".

 

Thanks for that Ken

[Ken H.]

My understanding is that the fuel pump injection on the hexheads only pumps as much fuel as the bike needs, in contrast to the setup on the oilheads that pumps a lot a fuel and returns the excess to the tank.

Not true. The hexheads have a return line from the pressure regulator just like always.

[smiller]

Not true. The hexheads have a return line from the pressure regulator just like always.

Yes, most all fuel injection systems work that way. And non-serviceable 'self cleaning' fuel filters are not unique to BMW, many vehicles are so equipped these days. I guess we'll know how well that all works in a few more years when we start to have a lot of these vehicles with 50-75-100k miles on them.