1986 K75c - Fuel Tank Vent Hose Rounting

[Laitch]

. . . I have done everything in the sodding book . . .

You haven't written that you have adjusted the valve clearances, only that you intend to do so. You haven't written that you determined why one throttle body needs significantly more adjustment than the others according to your bottle manometer. You haven't written that you've done a thorough test of the coolant temperature sensor, or have you? You haven't written that the Hall Sensor is correctly aligned, or have you? You haven't written that you've checked the condition of the spark plugs after one of these low mpg rides, or have you? Have you determined the fuel pressure? Is it warm enough in the Motherland to do these tests yet? If fuel puddling isn't onto the floor while the engine is running, the fuel path seems intact.

[szabgab]

You haven't written that you have adjusted the valve clearances, only that you intend to do so. You haven't written that you determined why one throttle body needs significantly more adjustment than the others according to your bottle manometer. You haven't written that you've done a thorough test of the coolant temperature sensor, or have you? You haven't written that the Hall Sensor is correctly aligned, or have you? You haven't written that you've checked the condition of the spark plugs after one of these low mpg rides, or have you? Have you determined the fuel pressure? Is it warm enough in the Motherland to do these tests yet? If fuel puddling isn't onto the floor while the engine is running, the fuel path seems intact.

HI Laitch, yes, I did some of the above, valve clearances were sorted over the winter as were the injectors. The coolant temp sensor was checked as a first thing back in September at the computer, as recommended by you and the others. I can not check it now, as it is still a tad cold outside to get the bike boiling over (top daytime temp is 10-15C). The spark plugs are OK, tan coloured with a very slight hint of white. As to why there is difference in throttle bodies is unknown to me, most likely because the butterflies open slightly differently, but Gryphon has got the same situation and his bikes are running fine. Fuel pressure has not been done, neither was compression, as I am still waiting for the slow boat from China. Hall Sensor was not touched, as a failing one would give me all sorts of driveability problems, wouldn't it? So yes, you are right, everything was not checked. All the external fuel lines were replaced by me, so I hope, there will not be any puddling in the near future :)

[szabgab]

Look closely at rbm's photo,  the pipe from the burrito exits the tank at the rear,  right underside of the tank,  its for air,  not fuel.

The photo shows the fuel return pipe roughly parallel with the burrito, but your's has possibly been cut.

I took gryph's post as a joke as if you get gas if you eat a burrito.

Maybe give your bike a full service and do the air fuel ratio test,  it takes all of ten seconds.

Daveson, I am still confused, sorry I am just thick at times... I have made a picture, I will attach, maybe you could explain to me, what you have meant, as I am at loss. As I understand, the narrow pipe, that is coming out of the burrito is for fuel vapours exiting the tank. That line was at the beginning of K production connected to the crankcase, at a later date that connection was omitted and both outlets - water drain from the filler hole and the fuel vapour drain were directed into the plastic cup, that is sitting on the frame, just below the tank and the narrow nipples protruding from it.  The barbed pipe might not even enter the burrito, hard to tell from the pics and unfortunately I can not see that in detail even on the bike. It is very obvious, somebody has done something the the pipes on my bike, but I do not know what, as I was looking and feeling around, if I notice a cut line coming from the burrito, but I could find none. I might even obsess over something, that is not important, if that is the case, I am sorry for that...

Now for the pic>

[daveson]

The fuel return does not enter the burrito. It goes behind it in the photo, turns left parallel to the burrito,  but behind it.  It is at all times outside the burrito. Then,  you can see it popping back into view. The burrito is for vapours only, it's purpose is to prevent fuel entering the vent pipe which exits the burrito and then exits the tank at the rear.

[szabgab]

The fuel return does not enter the burrito. It goes behind it in the photo, turns left parallel to the burrito,  but behind it.  It is at all times outside the burrito. Then,  you can see it popping back into view. The burrito is for vapours only, it's purpose is to prevent fuel entering the vent pipe which exits the burrito ant then exits the tank at the rear.

Oh, ahhhaa, I see... I do not see the return line popping back into view but that makes sense, thanks for that! So now back to Laitch's suggestion of fitting a piece of submersible line to the cut-off stub in order to get rid of the cicadas :)

[daveson]

You can see the end of the fuel return pipe pop back into view, but you have labelled it as a barbed pump breather.

[szabgab]

You can see the end of the fuel return pipe pop back into view, but you have labelled it as a barbed pump breather.

OK, I labeled it so, because that is what it is according to Laitch:

The short barbed pipe adjacent to the burrito collector is a vent pipe attached to the filter basket via a hose. The hose that attaches the two is not a high pressure fuel hose, it is a submersible vent hose.

There is a lot of misunderstanding of what is what, as the design of various components changed over the course of the production and obviously God only knows, what kind of a tank is on my bike manufactured in 1986 (but certainly replaced by the previous owner, as the original one was eaten by a too aggressive paint stripper). The pump assy inside was a hatchet job of a narrow aftermarket pump zip-tied to a deteriorating 53mm rubber insulator and it's filter basket without a hose attached

[daveson]

I think he is suggesting that the hose directs fuel from the return pipe to the pump to displace any air bubbles from cavitation caused by the pump.

Rbm explains that under his photo too.

Look at reply #4 by BrickMW. See the red line close to the burrito, that is possibly where your pipe has-been cut. Hopefully it has been supported somehow to regain stability. At least it looks stable.

My bike doesn't have that hose either,  and it runs fine.

By the way is your air filter good? Any obstructions to the air flow or exhaust?

[szabgab]

I think he is suggesting that the hose directs fuel from the return pipe to the pump to displace any air bubbles from cavitation caused by the pump.

Rbm explains that under his photo too.

Look at reply #4 by BrickMW. See the red line close to the burrito, that is possibly where your pipe has-been cut. Hopefully it has been supported somehow to regain stability. At least it looks stable.

My bike doesn't have that hose either,  and it runs fine.

By the way is your air filter good? Any obstructions to the air flow or exhaust?

Air filter is new, replaced in September, some 2000 miles ago. No restrictions, I am aware of, neither is the exhaust leaking.

Upon further investigation it looks like, the barbed pipe on mine is not connected to the burrito either... So I have a favour to ask, would you mind to check inside your tank, if the returning fuel is streaming out of that barbed connection, or some other place?

Thank you!

[The Mighty Gryphon]

My fuel returns through the barbed connection and sprays down onto the bottom of the tank a bit inboard of the fuel level float.  It is this way on all three of my Bricks, '94K75S, K75RT, and '91 K100RS.  There may be some minor differences in the later models compared to yours, but the operating principles are the same.

There have been two different filter screens for the fuel pump.  The earlier version looked like a basket  It had a stub on it that a hose from the fuel return barb connected to.  I guess that the idea behind the hose is to prevent pump cavitation caused by a dirty screen.

Later models had a larger screen shaped like a sock.  I suppose the larger filter area of the new style reduced the risk of cavitation so the hose from the return wasn't needed. 

I like having the returned fuel visibly splash in the tank.  It's an easy way to confirm that the fuel delivery system is working.  As far as noise, the only noise I hear from my tanks is the running of the fuel pump when I am down to 1-2 liters in it.  Kind of a final warning that I need to get fuel.

Regarding your fuel efficiency, 29-30 MPG is very low.  The lowest I have ever seen on my bikes is 38 MPG.  You say your plugs are tan and all the components are working correctly.  As far as I know, that only leaves the ECU and your odometer.  If the bike is performing properly and the plugs look good I would think the ECU is working properly.  That leaves the odometer.  I would suggest checking the tripmeter by riding a known distance.  A measured run of at least 20 km.  My experience is that the odometers are very accurate, but you never know.

Do you warm up the engine before riding off?  Are you frequently stuck in traffic?  I know from personal experience that can lower fuel mileage by as much as 10% depending on how far you travel. 

Another possibility is a slipping clutch.  Can you make the engine rpm's increase without increasing the speed, especially in 4th or 5th gear?  Dragging brakes can cause reduced fuel efficiency as well.  Is the bike easy  to push?

You mention MPG.  Have you measured your efficiency recently in km/l? 

[Laitch]

Hall Sensor was not touched, as a failing one would give me all sorts of driveability problems, wouldn't it?

The suggestion was to look at it, not touch it. A mis-adjusted sensor could affect performance without being a failing sensor—a timing issue. Until weather is suitable and you have the tools and opportunity to finish diagnosing your engine, you'll probably just need be satisfied with what you have.

The fuel seems to be getting to the cylinders regardless of the chop-job done in the tank that might have been done by its previous owners.

[szabgab]

The suggestion was to look at it, not touch it. An mis-adjusted sensor could affect performance without being a failing sensor—a timing issue. Until weather is suitable and you have the tools and opportunity to finish diagnosing your engine, you'll probably just need be satisisfied with what you have.

The fuel seems to be getting to the cylinders regardless of the chop-job done in the tank by its previous owners.

OK, is there a way to check, if the Hall Sensor is in the right place? Or am I asking something that is obvious and described in detail in numerous posts? :)

Fuel is getting where it should, mainly because I replaced that crappy pump and the clogged fuel filter a while back, now there is a proper stream of returning fuel (and hence an army of cicadas inside)

I have taken the plugs out today to check again, they look OK to me:

[The Mighty Gryphon]

I would say that your plugs look very good, maybe even a tiny bit on the lean side.  Your fuel/air mixture is pretty good, along with the other operating conditions like cooling, etc.

You mention the army of cicadas.  Are you absolutely sure the isolation damper for the pump is installed correctly and the pump is not touching anything in the tank?  If the engine is running you should only be able to hear the pump if the tank is almost empty.

[Martin]

The 2v Bricks have a built in mixture check. With your bike idle set at 1000RPM press the green start button. If the mixture is correct the idle should stay the same or rise slightly if the idle rises significantly it's lean if the RPM's drop or it dies it's too rich. There are a couple of ways to adjust the mixture 1/ The lean drop method instructions on this site 2/ Use an exhaust gas analyser.
Regards Martin.

[daveson]

Ay Martin,  how does it work ay.

I've used your tip on all my bricks,  luckily they have all been good. How does pressing the button alter the mixture? Is there a way to understand it,  or is it by computer magic?

[Martin]

When you press the green button it richens the mixture. I've been told that after 711 RPM the computer stops the starter from engaging, I haven't checked it. I do my checks at 1000RPM. Some have alluded that pressing the starter while going can be used as a boost, I did try it and it didn't make any difference. :tinhat2
Regards Martin.

[daveson]

Thanks,  that makes sense.

[daveson]

Ay Gabe (sorry there's too many syllables in Gabriel)

I can only get to my '92 k100 today. It's way different plus it was made from pieces by the previous owner. The fuel return pipe is welded to the filler area and does a u turn, the fuel lands on the raised centre portion of the tank at the front. There is a mini burrito, smaller than the fuel pump relay. There is a barb on the left,  fuel does not exit it. BrickMW's photo shows the barb as the return exit. The barb on the left on my bike is noticeably smaller in diameter than the return pipe so is probably a vent for the old style pump. The diameter of yours might give you a clue.

Since Gryph's also exits on the right, maybe yours hasn't been cut, maybe it had a hose that was roughly removed, bending the pipe,  so that it now unfortunately squishes the fuel between the top of the tank and the burrito.

Have you done a compression test? Are all exhaust headers equally hot?

[daveson]

Is the returning fuel causing the float to tap against the side wall of the tank?

Filter, hose or cables tapping against anything?

If your feeling lucky you would only have to bend it a little, so as to avoid the burrito, well are you?

Maybe bend the float wire too, if its too close to the wall.

Your exhaust may not be leaking, but is it partially blocked, and are there swishing, hissing sounds coming from it?

[szabgab]

My fuel returns through the barbed connection and sprays down onto the bottom of the tank a bit inboard of the fuel level float. 

There have been two different filter screens for the fuel pump.  The earlier version looked like a basket  It had a stub on it that a hose from the fuel return barb connected to.  I guess that the idea behind the hose is to prevent pump cavitation caused by a dirty screen.

Regarding your fuel efficiency, 29-30 MPG is very low.  The lowest I have ever seen on my bikes is 38 MPG.  I would suggest checking the tripmeter by riding a known distance.  A measured run of at least 20 km.  My experience is that the odometers are very accurate, but you never know.

Do you warm up the engine before riding off?  Are you frequently stuck in traffic?

Another possibility is a slipping clutch.  Can you make the engine rpm's increase without increasing the speed, especially in 4th or 5th gear?  Dragging brakes can cause reduced fuel efficiency as well.  Is the bike easy  to push?

You mention MPG.  Have you measured your efficiency recently in km/l?

You mention the army of cicadas.  Are you absolutely sure the isolation damper for the pump is installed correctly and the pump is not touching anything in the tank

Gryphon, I somehow completely missed your first response, sorry. As there is no fuel coming out of the barbed end on mine, we can safely say, the return line has been cut and the remaining stub cut off up to the barbed end, as I can not find the missing piece by feeling around the collector. No biggie as long as I know from Daveson's reply, that line never enters the burrito. I will get a length of submersible line connected to the cut off end, even though there will be no barb to retain it, so it might slip off eventually. The army of cicadas is the noise, splashing petrol makes first on the edge of the burrito then hitting the wall of the tank. The pump starts it's noisy operation, when I am really low on petrol, just like on yours, I guess the empty tank becoming a resonance chamber.

Fuel consumption wise, I have converted l/100km to MPG, I should have gone to fuelly straight, as I see, I have made a calculation error - please see my profile at http://www.fuelly.com/motorcycle/bmw/k75/1986/szabgab/840106/fuelchart Disregard the first fuel up, as that was, when I have gotten the bike and it was partially filled by the PO, so that reading is better, than anything else measured by me. Also there was a really bad 8.2l/100km consumption in December, but I must have been so shocked, I forgot to log it :) I do a lot of city rides, basically the bike lives in the metro area rarely venturing further, than let's say 20 miles, I do warm up the bike before take off and being inpatient I chose routes, where I do not have to be held up by the cagers too much.

Clutch is not slipping fortunately, however I did have problems with my brakes, especially the rear one dragging slightly. That is an odd one, as the bike is very easy to push since servicing all three calipers and master cylinders, but somehow the rear rotor still gets hot to the touch after rides.

[Laitch]

As there is no fuel coming out of the barbed end on mine, we can safely say, the return line has been cut and the remaining stub cut off up to the barbed end, as I can not find the missing piece by feeling around the collector. The pump starts it's noisy operation, when I am really low on petrol, just like on yours, I guess the empty tank becoming a resonance chamber.

I believe we can safely say none of that. I believe you have a later model tank that is exhibiting classic noisy pump symptoms caused by fuel not being returned to the most effective location for uptake when the fuel volume is low. I alluded to this and its remedy in an earlier post. Fuel is coming from the correct pipe in the correct location within your moto's tank. I've attached to this post a service bulletin that describes this condition. In the service bulletin's low-quality illustrations, notice the size and location of the pipe into which the prying tool is inserted. A ghostly burrito appears to the right of the pipe. The pipe looks to me like the one dumping fuel in your first video. The pipe is being carefully pried away from the burrito to allow room for the hose and its clamp. Use of a high-quality fuel injection hose clamp to attach the hose to the pipe should fasten it securely to the pipe. This is something you can do.

I do a lot of city rides, basically the bike lives in the metro area rarely venturing further, than let's say 20 miles, I do warm up the bike before take off and being inpatient I chose routes, where I do not have to be held up by the cagers too much.

It's unreasonable to expect low fuel consumption if the bulk of your riding is short haul in cold weather on a moto that has not been fully tuned. Short-duration cold weather riding is hard on engines even with a warmup. The warmup is mainly effecting water temperature. Lubrication needs more time in circulation to perform optimally and increase engine efficiency. Once weather warms and you've completed your engine maintenance, fuel consumption will probably lessen. The moto needs distance riding to get it in shape. Use your scooter for commuting. Put skull decals on it to give it street cred, if you haven't done that already. :giggles

A 10-year old Prius up here in the mountains drops from 45–55mpg in mild weather down to 38mpg in winter.
 

[Laitch]

The coolant temp sensor was checked as a first thing back in September at the computer, as recommended by you and the others. I can not check it now, as it is still a tad cold outside to get the bike boiling over (top daytime temp is 10-15C).

You could check it right now because it doesn't matter how cold it is outside. The coolant temperature sensor is removed, immersed in boiling water, connected to the leads of a multi-meter, then as it cools, the resistance values are compared with widely-accepted specifications. Admittedly, parts need to be removed to access the sensor and that task certainly could be inconvenient for a self-described impatient man on the go.

The plugs look good though, so the task seems optional right now.  :yippee:

[szabgab]

The 2v Bricks have a built in mixture check. With your bike idle set at 1000RPM press the green start button. If the mixture is correct the idle should stay the same or rise slightly if the idle rises significantly it's lean if the RPM's drop or it dies it's too rich. There are a couple of ways to adjust the mixture 1/ The lean drop method instructions on this site 2/ Use an exhaust gas analyser.
Regards Martin.

HI Martin, I have tried that a few times before, pressing the starter button does absolutely nothing, so I guess my mixture is OK.

[szabgab]

Is the returning fuel causing the float to tap against the side wall of the tank?

Filter, hose or cables tapping against anything?

If your feeling lucky you would only have to bend it a little, so as to avoid the burrito, well are you?

Maybe bend the float wire too, if its too close to the wall.

Your exhaust may not be leaking, but is it partially blocked, and are there swishing, hissing sounds coming from it?

Dave, the hissing sound is very obviously coming from the tank if you are next to the bike. It is (was) the fuel stream hitting the burrito full blast and subsequently the wall of the tank

[szabgab]

The coolant temperature sensor is removed, immersed in boiling water, connected to the leads of a multi-meter... Admittedly, parts need to be removed to access the sensor and that task certainly could be inconvenient for a self-described impatient man on the go.

The plugs look good though, so the task seems optional right now.  :yippee:

:) For some reason I am impatient with city traffic only when riding a bike (although seeing all them others race off from red lights and so on is not my world), I drive a car like a grandpa on sedatives.

Would this extensive test be necessary, if the values measured at the computer are well within specs?

What about the HES? Is there an easy way to tell, if timing is correct?

Thanks!