BMW K bikes (Bricks)

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Beamer

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Hi,,

I'm having serious trouble the my K75, since I had a batch of bad petrol it's gone from bad to worse and is basically unridable.

It starts  and runs so  badly it's barely able to pull away. Once it warms up it gets a litle better but still runs as rough as guts and barely makes 140 km/h flat out.

I purchased a new Bosch  fuel pump since the pressure was low on the old one ( circa 0.5 bar ! ) and seemed  to have taken a hit with all the crap in the tank. I know the old one was weak already so figured this must be the problem. It changed nothing !

Last week I put some injection cleaner product with the last tankful in case that could clear out the injectors.

I have changed the plugs and today swapped one of the injectors since I figured they were next in line with the fuel problems. Having pulled them out one seemed to be spitting nothing so I though I'd found it. I swapped the electrical connections to ensure that it was the injector itself and not the wiring. Having established that the problem stayed with the same injector I replaced it with a serviceable replacement. All three were spitting a similar looking jet to I figured that was OK. 

It changed nothing. No even a bit better :?   Exactly the same behaviour as before.

I have put the strobe light on it and the timing is close to the mark and seems regular on all three cylinders.

I have put the Hg columns on and all three are nearly equal and rise and fall in a similar way. I don't have a compression gauge but figured this test would have shown if I had a weak cylinder.

I have checked the plug on the fuel injection unit and all is clean and undamaged.

It will tick over for a while though only around 600 rpm. On start up , all three pipes got hot straight away which goes against one not firing at all.

I'm running out of ideas.  Can anyone suggest another thing to look at?

Thanks.

    

charlie99

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did you replace the fuel filter whilst you were in the tank ?


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'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%O
    

MartinW

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+1 on the fuel filter. Check the "Z" hose and the vacuum caps on the throttle bodies. Check for air leaks around the throttle bodies. Check the fuel pump regulator, and the vacuum hose that runs off the No3 vacuum port. And one that nearly caught me out check the fuel return line for kinks (thanks Charlie).
Regards Martin.

    

Beamer

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thanks all.

yes filter got replaced before the pump did. First thing after the crap petrol . I need to get a pressure gauge capable of going  to >=2 bar to see new fuel pressure in situ. I was wondering about the pressure regulator playing up.

I will check for air leaks but this all started after I bought the enema bilge water from the local super market's petrol pumps.

Still, once you have eliminated all possible causes, all that remains is the impossible.

    

MartinW

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A while ago I built a rig for testing injector spray patterns. Check to see if you have the correct pattern.
Regards Martin.

    

MartinW

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The 2V Bricks had a really neat little used self test feature. Get your Brick up to temperature and set the bike to idle at 1000rpm + this test will not work under 1000rpm. Next press the green start button, if the mixture is correct the idle should stay the same or rise very slightly. If the revs drop or it dies the mixture is too rich, if the revs increase significantly the mixture is too lean. When my Brick had a kinked return line pressing the button stalled out the engine due to it being way too rich.
Regards Martin.

    

Beamer

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yes, I was wondering about that.  Though I figured if I was getting about the right dose it should at least be running.  I'd say from what I saw it was more like the left one in your photo. Not much spray or dispersion. More of a squirt.

    

MartinW

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It should be a squirt see previous post on testing. On my Brick it was also one of the final pieces in the puzzle to solving intermittent backfiring on overrun. http://www.k100-forum.com/t12921-oem-fuel-injector-spray-pattern
Regards Martin

    

Point-Seven-five

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Is the fuel filter in backwards?  That is something I would do.

As long as I'm thinking backwards, are the tank connections to the fuel rail and regulator return on the correct spigots.  That's something else I could do.

Is it possible there is some water in the fuel tank?

Pull the fuel line from the tank to the rail and run the fuel pump.  Correct volume of flow is about .5 liter per minute.

If indeed there is actual dirt that got to the injectors, injector cleaner probably won't help.  Cleaners have solvents to soften and dissolve the varnish that forms when fuel goes bad.  They will not work on common dirt which can usually be insoluble mineral particles.  With any liuck if there is dirt in the injectors, it will mostly be in the metal filter at the injector input.  Those filters are available at your local auto parts outlet and are fairly cheap.


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Present:
1994 K75RT
1994 K75S
1992 K100RS

Past:
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

Beamer

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it will mostly be in the metal filter at the injector input.

Ah that's worth knowing, I did not realise that there was another level of filter.

I will check the direction of the petrol filter.  I know there is a direction arrow but I have an alter-ego who does shit like that to me from time to time. I'm pretty sure it went in right, but everything has to be double checked at this stage.

I'm going to test for air leaks tomorrow even if that is also improbable that it sprung an air leak at the same time as the other problems. Obviously the stars are not in a favourable configuration at the moment. Probably the bloody blue moon thing or a conjunction of Beatlejuice and Uranus.

    

MartinW

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There is a small mesh filter situated in the inlet of the injector. In order to remove it, screw in a self taping screw of the appropriate diameter and pull out using vice grips, pliers or a vice. Extraction normally renders the filter screens unusable.
Regards Martin.

    

Beamer

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From Martin's link:

1. Good spray pattern but weak supply (clogged filter)

Could be suffering from that but not sure that is serious enough to get to the stage of not even being able to pull away.

some 'budget' retailers of petrol who decline to add sufficient amounts of polyetheramine to the base petrol.

More like frog-spawn, swamp weed, bilge water and gravel. ( All at no extra cost.)

    

Beamer

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I checked the compression  and I got a pretty even 9 bar on all cylinders. Volumetric ratio is  11:1 on K75 it seems.

I measured with throttle wide open and spinning the motor on a fairly good battery.

What sort of figure should I expect for measured compression on these bikes?

    

MartinW

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Should be 8.5 to 10 Bar, so you are fine. Due to variations in compression gauges, and the fact that once bought they are never serviced or calibrated, even readings are more important. 
Regards Martin.

    

Beamer

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Thanks very much. That's reassuring. I know there are a lot of variables that change measured compression, so it has to be compared to the same vehicle in similar test conditions.

It's a new gauge but only a cheap car shop model.

At least if it's in the right range that's another box checked off.

    

Crazy Frog

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@MartinW wrote:A while ago I built a rig for testing injector spray patterns. Check to see if you have the correct pattern.
Regards Martin.
I totally forgot about that, but in 1995, I built a similar test rig for the fuel injectors of jet engines. It was testing one full segments at the time (maybe 12 injectors, but I don't remember). The injectors could be turn 90 degrees (facing you or facing down)
It had 2 function:
Spray pattern (It was spraying on a fix piece of plexiglass where the right pattern was printed on).
Flow rate by spraying down into graduated recipients.


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1986 k75, 1985 K100rt, 1985 K100rt/EML sidecar.
    

Crazy Frog

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There is something that nobody talked about..... Water temperature sensor and Mass air flow sensor(MAF) or, the throttle position switch (TPS).

If you don't have any air leak (Even the engine oil filling cap could be a problem if it's not tight)

First thing is to disconnect the TPS (Easy and no cost)
Second thing is to check the water temperature sensor (more difficult to access). If the reading is false, the engine may run on poor or rich mixture. (The color of the plug should give you and indication)
The last option is the MAF. If the vane is not moving freely, the engine will not get more fuel when you open the throttle.
I suggest a good reading of my EFI troubleshouting page in order to understand the relation between all the components of the fuel injection system.


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1986 k75, 1985 K100rt, 1985 K100rt/EML sidecar.
    

chris846

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Hi, I am full of sympathy - most of us will have been in this situation many times with different bikes. For me, each time it was something really really simple, despite me convincing myself it must be something unfathomably obscure.

Example 1: bike rode normally enough at lower revs/speeds, but just wouldn't rev out, no matter how hard I tried to make it! Cause: blocked fuel filter - recently fitted so not suspected, but I had not long since replaced the tank with a secondhand one that had been full of dried fuel that I had mostly washed out (but not enough, obviously) The dried fuel had loosened over a couple of weeks and the tiny gummy lumps had soon choked up the new filter. Before I found the real cause, I had bought and fitted a wideband AFR meter, variable fuel pressure reg etc. etc.

Example 2: a oilhead boxer, ran rough & smoked, didn't want to rev, took it on the motorway to try and 'clear it out' (yeah, that works...) and it seized. Rebuilt it with a new barrel and piston, did exactly the same. Spent lots. Cause: local petrol station had sold a batch of petrol mixed with diesel - that was what I had in my tank. Yep, if you can get it to run a bit with diesel in a nikasil bore, it will seize it.

Example 3: my project bike - built a plenum chamber to my own clueless design, bike wouldn't rev past 4000, swapped everything, convinced myself it was resonance or whatever in the plenum. Actual cause: an iffy HT lead that didn't like being in a tight radius.

Just trying to offer some encouragement, it's most likely something simple and not too unrelated from the problem fuel. Maybe look at your plugs. They could be gummed up in the annulus around the electrode, even though they look clean. I've had that happen after an extended spell of rough running for some or other reason and it weakens the spark in an otherwise perfectly good plug. You could try and clean them with a wire/cloth but the best thing would be to swap for a new set.

Good luck!

Edit. Apologies, I reckon to read the thread so's I don't go and idiotically suggest something you've already tried. Missed the bit about you already swapping the plugs.

Bearing in mind Example 1 - a new fuel filter can clog up really quickly if there's still some crap around in the sytem, you could try quickly bypassing the filter inside the tank?



Last edited by chris846 on Mon Feb 05, 2018 4:03 pm; edited 2 times in total

    

Beamer

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Thanks for the tips CF. I am very familiar with your guide, a fine reference work on the subject.

I posted a very detailed study of renovating the MAF sensor on this forum, so I'm confident I know how that works.

I think I posted above that the plug colour looked good after giving it a bit of a run. Once warmed up it does run but badly , not getting beyond 140 km/h flat out.

I'll look into the points you raised about the various sensors, though I suspect that they are secondary factors and not likely to produce the extremely bad running I am seeing.

Thanks for your comments.

    

Laitch

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In your opening post, you seemed to tie together the use of contaminated fuel and a concomitant drop in engine performance. That would indicate all fuel delivery components should be checked. Did you clean the interior of the tank after this mishap, remove all fuel lines to determine whether the delivery and return lines are partially blocked and clear them with compressed air? Have you determined the fuel injector fuel delivery rates? Have you checked the vacuum line to the fuel pressure regulator and the regulator itself for proper function?

In post #4, you stated you'd be checking for air leaks. If you haven't checked the bike's crankcase z-tube and checked for faulty vacuum caps along the throttle body, those probably should be inspected—as has been previously suggested—although malfunction in them probably wouldn't be caused by one serving of contaminated fuel.

As chris has observed, these pesky conditions are often resolved right after somebody says, "Well I'll be dipped! This thing here isn't plugged in right." Smile


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1995 K75T 68,000 miles
    

MartinW

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Did you check the fuel return line as I stated I had problems with mine running badly. It was due to a crimped return line. You need to let us know what you have checked as per the inmates  suggestions.
Regards Martin.

    

gabriel


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hi

Have you considered the battery.

    

gabriel


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hi

Have you considered the battery.

    

Beamer

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As chris has observed, these pesky conditions are often resolved right after somebody says, "Well I'll be dipped! This thing here isn't plugged in right."

Well, I'll be dipped.  ( not sure that's exactly what I said ).

Having checked for air leaks, I went back to check the pressure of the new pump. It seemed improbable that I'd bought duff one that could only manage one bar.  I put the pressure gauge back on and pressed the tit.  Still 1 bar, but it suddenly hit me that what I had assumed was the frothing of the fuel return could not be that because the fuel ramp was not connected.

I looked inside the tank and saw petrol squirting back , I realised it was around the fuel filter. In fact the 2 inch bit of tube linking the filter to the ali tube leaving the tank.

I whipped it out and though in good condition it had a short split along its length. Almost as though cut with a razor blade. That is why I had poor pressure and doubtless by the old pump was even worse ( 0.5 bar ).  Having replaced it I have tons of pressure and the bike is running. No good but running.

I think this has been going on for a while because I'd noticed this squirting before but just thought it was the return line.

I will not have to look at the flow meter bypass , timing etc. which probably can now be set to run much better. Last time I checked the timing it would not run well if I set right, so that was probably part of the story too. 

Many thanks for all the well informed comments and suggestions.


Hi, I am full of sympathy - most of us will have been in this situation many times with different bikes. For me, each time it was something really really simple, despite me convincing myself it must be something unfathomably obscure.

This astute comment was on the money , though it did not tell me where to look, it probably helped me focus on the problem.

Thanks to all. Wink

    

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