How do I drain the fuel tank in my 1991 K 75 RT ?

I'm thinking I may have water in my gas. I first thought a hose maybe off inside the tank, and siphoned most of the gas out ,but not all.. I would like to drain the whole system, but not if it's difficult .
If water is my problem it's probably clogging the injectors ,or something in the pump..
Someone suggested using " Heet" to get rid of water in the lines , I have no idea about fuel injection systems ..
I have fresh gas here ,but with water plugging EFI's close tolerances I'm not sure what to do .. I'm not sure irt's water causing my problem, but it seems most likely ..

With the tank removed, insert a wire or similar up into the return line stub on the bottom of the tank. It has a ball type check valve. The wire will raise the ball and allow the fuel to drain.

Thanks , I'll take a look at what's involved in removing the tank . I am not used to working ion a BMW . so far everything seemed scarey, my Haynes , and Clymer books both open beside ,me ! LOL .
















until I got into it

xcaret said:

Thanks , I'll take a look at what's involved in removing the tank . I am not used to working ion a BMW . so far everything seemed scarey, my Haynes , and Clymer books both open beside ,me ! LOL . until I got into it

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Before you do that, just put in some Heet and a little fresh gas. Water in sufficient quantity can clog a filter and even clog injectors but that is rDumping the tank will not unclog a filter. If it is water logged then replacement is needed. But before doing all of that just use some IsoHeet in the red bottle.

PGlaves said:

With the tank removed, insert a wire or similar up into the return line stub on the bottom of the tank. It has a ball type check valve. The wire will raise the ball and allow the fuel to drain.

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Paul,

You must be thinking of Voni’s R bike. The early Ks return line (forward nipple on left side) is a solid line that goes from the outside up into the double walled roof of the tank. There is no check valve and fuel (other than what is in the line itself ) will not drain out of that port.

The next nipple back on the left is the pressure port. It is connected to the filter and the pump, so it is not a good way to drain the tank.

The easiest way to drain the tank is with a pump. Harbor Freight and Summit Racing both sell this battery powered pump that works very well.

https://www.harborfreight.com/batte...sfer-pump-63847.html?_br_psugg_q=battery+pump


I agree, it is most likely water in the bottom of the tank or the filter is trashed from water. The filter can be checked by removing it, emptying it, and then letting it dry out over night. If you can then lightly blow through it with resistance similar to a large milkshake straw, then it is fine. The higher the resistance, the worse it is.




That is IF the pump is working. With the fuel cap open, hold open the silver flapper (if it still has one), put your ear near the filler, turn the key on, in neutral, and TAP the starter once. The pump SHOULD run for about two seconds. If it doesn’t, you could have other problems.

98lee said:

Paul,

You must be thinking of Voni’s R bike. The early Ks return line (forward nipple on left side) is a solid line that goes from the outside up into the double walled roof of the tank. There is no check valve and fuel (other than what is in the line itself ) will not drain out of that port.

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Look up this part number. Said part screws into the bottom of the fuel tank, the piping inside the tank notwithstanding. I think it is in the return line.

https://www.euromotoelectrics.com/product-p/ftvalve348.htm

Paul,

The only tanks that I’ve seen that had that valve were ‘85 and older K100s.

I have 14 tanks here (8 loose and 6 on my bikes). None have any threaded connections on the bottoms.


From Anton’s website:

The first K100 tanks (before 5/85) had:

a ball-type check valve in the return line. The resulting rattle annoyed many owners and it was removed
a rear mount that bolted on (which was prone to cracking)
strip-based level sensor which didn't work well
No provision for a screen on the fuel pump
a small vent chamber directly behind the filler opening.
In 1985 the tank was changed to add two mounting posts for the rear of the tank, replacing the flat plate and single bolt that was prone to causing tank cracks. An opening was made to allow a vent hose to run down from the vent chamber to the filter basket on the pump. This apparently helped when the fuel got very hot, which was a big issue with the early K100s.

In mid-1986 when the K75S was introduced (according to Clymer's) the fitting for the check valve was removed from the tank. From that point onward, all of the tanks had regular pipe stubs for the inlet and outlet. This indicates that the first year (1986 models) K75T and K75C may have had the threaded return fitting.

http://www.largiader.com/ Under: K75 fuel tank variations.


I know that the parts fiche shows that valve, but BMW’s illustrators were notoriously lazy (efficient?) If they already had panel (picture) from a previous model that was close with only minor differences, they would just copy and paste. Usually the editors would catch any differences and make changes in the text part by just eliminating the line, but they didn’t catch them all.

My 1986 K75T had that valve.

Given the sparse use I wonder why EME even handles this obscure part?

PGlaves said:

My 1986 K75T had that valve.

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That would be correct according to the last sentence of Anton’s comments.


There were alot of ‘85 K100s imported to the US. There have been alot of them with gunked up tanks due to the deteriorating pump vibration dampers. So I would imagine when the tank gets gunked, those valves get trashed.

Half of EMEs business used to be fuel pump kits for early Kbikes with trashed vibration dampers.

For a while you had me worried, Lee. I couldn't imagine that I dreamed up that valve bit out of plain air. I have not looked at any of out other several K bikes. Even disconnecting the hoses I didn't bother to notice the presence or absence of that valve.