K75 not starting ( let out your inner Sherlock Holmes)

[failedmechanicnico]

Hi,

after bookmarking about a dozen entries in this forum and checking everything I could possibly imagine I am still unable to start my K75c.


IŽll start from the beginning :
About a year ago I bought a 1985 BMW K75c to convert it into a Cafe Racer (please do not crucify me for this  :oldguy: ),

My Dad and I rode it and were very satified with the engine and the bike I general so I gave up my hard earned savings hoping to have a "bulletproof " bike for my upcoming build.
A couple weeks later I start stripping the fairing, do the oil changes, polish the engine, etc.
Then I put the tank back on an try to start the bike , which failed since the fuel injection had cosen that fuel shall not pass  :oldguy: (sry about that joke, just trying to keep it fun to read).
After trying out a replacement EFI computer I figured out that the problem was a faulty coolant temp. sensor. [The bike would run, with it disconected but not start when it was pluged in].
So I drained the coolant,swiched the sensors and did not try to start since it was christmas an my garage was freezing.

Now I come back home from University, wanting to finish my build and she just wont start.

But this time the symtoms are very different:

Starter turns   ,   the spark plugs fire  , fuel is injected(spark pugs are wet after), it even drips out at the conection of the exhaust and the silencer

So far I have checked the fuel pressure (OK) , the resitance of the temp. sensor (about what it should have been), replaced all 3 Spark Plugs and checked them ( they do all make a beautiul blue spark) ,checked the connection of the spark plugs to the coils and made sure the coils were connected right, checked that the airflow meter door is NOT stuck open,  taken out the airfilter before starting.

I have also tried to lean out the air fuel mixture by replacing the coolant with warm water to fool the temp. sensor.

Still nothing has helped an I have wasted a third of my semester break on this issue.

I have installed 3 "discs " to reduce power to 34hp (original and intended for this bike).

Anyone able to help me solve this problem would be the new Jesus and have my everlasting thanks. :euro

[Laitch]

I have installed 3 "discs " to reduce power to 34hp (original and intended for this bike)

Please thoroughly described this installation, its components and its purpose.

[failedmechanicnico]

The "disc" I have installed were made by Alpha Technik.

Just google "ALPHA TECHNIK 601489" and you should find an image of them.

IŽll leave this link to them below , but I dont know if I am breaking any rules with this:
http://www.rakuten.de/produkt/alpha-technik-601489-drosselsatz-drossel-bmw-k75-bmw75-85-91-55-auf-25kw-1723487604.html?cid=google_base&utm_source=gshopping&utm_medium=referral&utm_campaign=googlebase-2010-07&portaldv=6&sclid=a_google_de_pla_empty_www_zietech_de_698-405-8651_1723487604_c&gclid=COK22s2TmNICFZUV0wodmEkIdw

They are installed  into the rubber thing above the intake manifolds

[Laitch]

The "disc" I have installed were made by Alpha Technik.

Just google "ALPHA TECHNIK 601489" and you should find an image of them.
They are installed  into the rubber thing above the intake manifold

I get it now. You didn't qualify to ride a bike with that size engine performance so this nice company made it so your K would qualify for use with your license and, consequently, you would be safer.  Did it ever start with this gizmo in it?

You can always get rid of it if you want the bike to start, or discuss the problem with the manufacturer. Sherlock or Jesus will be along momentarily. 

[failedmechanicnico]

By european law  :nono  I am only allowed to ride up to 48hp (until next year).

[Laitch]

By european law  :nono  I am only allowed to ride up to 48hp (until next year).

See my post above yours.

[failedmechanicnico]

Unfortunatly I did not try to start the bike before installing them.

 Still I doubt that the problem is caused by this, since these things undergo extensive testing and were installed on thousands of bikes.
Also I cant imagine them restricting the airflow so much that the bike would not start.

I do appreciate your help but I think removing them and trying to start without them would be a lot of effort and strain on the rubber.
But unless anyone comes up with a different answer IŽll try it out this weekend.

[Laitch]

Also I cant imagine them restricting the airflow so much that the bike would not start.

Sometimes products don't work as advertised. Clearly, by your description, there is too much fuel in the mixture. That will keep an engine from starting. Talk to the manufacturer. If this scheme has worked on "thousands" of bikes maybe you missed a step in the installation. They might be able to help you.

I personally cannot envision a K75 working well with this system. I hope it works for you and that you report back with results.

[Elipten]

Engines are basic. Air, fuel, in proper ratio, ignition source and then the compression with proper timing of spark

Fuel leaking out says too much fuel

Did it run before installing the 'disks'?

If so remove them, dry the cylinders and plugs and see if it runs

If it does you know the source of the problem

I always suspect modifications in a case like this


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[The Mighty Gryphon]

Two possibilities come to mind. 

First, the injectors are delivering too much fuel.  Are they stuck open?  Is there a problem with the Jetronic signal to the injectors?  Have you checked the spray pattern and pulsing?

Second, there is a problem with the fuel.  How old is it?  Is there water in it?  Have you drained the tank and tried fresh fuel?   Are you trying to use fuel purchased in the summer?  Summer fuel does not atomize well in cold temperatures.

Bonus problem:  Are you holding the throttle open?  These engines are designed to start with the throttle closed.  Just use the "choke" lever on the left handlebar.

[Martin]

+1 Too rich the restrictors are not allowing enough air in. Try starting without touching the throttle or remove the fuel pump fuse #6 pull the plugs and dry them out, crank over the engine to push out excess fuel. Replace the plugs and try and start the bike, it should start, as the engine starts to die replace the fuel pump fuse. It will help if you have an assistant to either replace the fuse or work the throttle.
Regards Martin.

[The Mighty Gryphon]

Martin, the restrictors aren't blocking air flow when starting.  They probably don't do anything at less than 1/4 throttle.  They won't restrict air flow until the throttle butterflies open to an area larger than the hole in the restrictor plate.

[Martin]

 :2thumbup: Still sounds like it's flooding.
Regards Martin.

[Laitch]

I understand from your first post that the bike was running well after your bodywork modifications then you installed the restrictor and it would not start. Is that correct?

The AlphaTechnik kit seems to be an airflow reducing restrictor in this case rather than a throttle stop restrictor. The company recommends its being installed by a professional.

The K75 develops a fuel sending signal partly based incoming airflow entering unrestricted throttle bodies. It makes sense to me that there would be excessive fuel in the mixture after restricting air volume unless the system was modified to account for reduced air volume caused by the restrictor discs.  I wonder how this kit adjusts fuel delivery volume to accommodate the restricted intake volume at the throttle bodies. That would seem to need a modification of the fuel injection control itself. What exactly was supplied in the kit?

[The Mighty Gryphon]

Laitch, the MAF sensor determines the amount of fuel injected.  By measuring the actual amount of air flow into the engine it will automatically compensate for the restricted air flow. 

If the bike had the typical Mikuni carbs of my misspent youth, there would be all kinds of jetting changes to be done. 

Those restrictor plates are an elegantly simple, reversible solution to the need to reduce engine output.  Probably why even Nascar used them.

In any event it looks like we chased off another newbie.

[Elipten]

Since my German is about 40 years since last use, not much ability to read the page in the link.  All I see are three significant restrictor plates and three new clamps in the picture.

Can you show,or explain what, where, the kit was installed?

You have instructions in English?.

My instinct says the restrictor kit is the issue.


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[The Mighty Gryphon]

The restrictors go in the bushing above the throttle body.  They restrict the airflow through the throttle bodies when they are open more than about 1/4 way.  At anything up to 1/4 throttle they have absolutely no effect on the airflow.  The restrictors limit horsepower at wide open throttle settings, basically reducing acceleration and top speed.  They have NO effect at idle or nearly closed throttle settings. 

As I mentioned above, they need no tuning with the fuel injection system of the K75.

[Laitch]

Since my German is about 40 years since last use, not much ability to read the page in the link. 

I use Google Translate, Elipten. The website url gets copied then pasted into its left hand box. Above the box the language of the site is selected. In its right hand box English is selected. When the content of the url is displayed in the left hand box, the right hand box might display a translation or a mix. Click the blue Translate tab above the box then the whole translated website will appear. Sometimes there is a disclaimer box at the top that requires Dismiss to be clicked.

It does a pretty fair job of making things understandable. In this case I couldn't find a link to pdf installation instructions on the site.

[Laitch]

. . . they need no tuning with the fuel injection system of the K75.

Not convinced yet. Still waiting for Jesus or Sherlock. 

[John Lang]

Those power reduction throttles are static and do not interact with the electronics so perhaps Bert Vogel's flow chart can help.


http://hrsbstaff.ednet.ns.ca/bvogel/K100/download/bike-wont-start1.htm

[failedmechanicnico]

Thanks for your help so far,

later today I  will remove and test the Airflow meter , since it is something easy and quick to do.

Tomorrow when the shops open again I will get myself a 12V LED to test the electrical power at the fuel injectors also I might take them out and check the spay pattern if necessary,but if I do that IŽll have to wait till tuesday to get the new O-Rings. Still the probability that all 3 injectors were stuck open or in some other way malfunctioning at the same time is pretty low.

In my opinion everything points to a sensor or EFI problem and if the restrictors / discs/ reduction throttles were the problem then opening up the throttle a little should be enough to let more air into the engine ( although I donŽt know how that would influence the amount of fuel injected ), which it isnŽt.

IŽll be back with more this evening.

[Laitch]

In my opinion everything points to a sensor or EFI problem and if the restrictors / discs/ reduction throttles were the problem then opening up the throttle a little should be enough to let more air into the engine ( although I don't know how that would influence the amount of fuel injected ),

You are approaching this in an orderly way so I think you might turn out to be your own Sherlock.  You seem to have already substituted an EFI with no change in results. Using a multimeter and following Bert Vogel's troubleshooting chart from beginning to end is a good approach as Martin indicated.


What stands out to me is that the bike functioned before the throttle restriction modification. If the modification itself is not the source of the problem then it might have occurred during the reassembly of the fuel system and electrical components. Checking all the throttle body linkage connections is probably on your schedule already.

[failedmechanicnico]

Testing the airflow meter and air temp. sensor revealed nothing new ,
tomorrow IŽll check the TPS and do the LED check on the injectors.

IŽm pretty optimistic that by tomorrow IŽll know where the problem is.  :riding:

[John Lang]

Think back carefully. Did you accidentally auftanken with clean Diesel? :-)

[failedmechanicnico]

I should patent this technology and sell it to VW, youŽll pass any emissions test if the engine doesnŽt start  :hehehe

I think I have solved the problem now, it seems to have been a bad connection to the water temp. sensor .
I took it out and short circuited the connector (from the EFI) them measured the resistance and still got 4500 Ohm and the bike started.

IŽve ordered new cables which should arrive late this week.

Thank you for all the help
Turns out I didnŽt really need Sherlock or Jesus to solve this one :bang-head: