EDIT: Preface, this bike was abandoned outdoors for 5 years before I tried starting it

I have replaced in-tank fuel lines, the fuel pump, and fuel filter. Along with a new battery, I tried to start my '88 K100RS. Here's a video of the attempt. How's it sound??



No start. Could be no spark? Or bad injectors? I tested the injectors first.

I think some people advise pulling the fuel rail to inspect the spray (e.g. onto some cardboard). It was too difficult remove because the injectors were firmly gummed into the engine block, so I disconnected and pulled them out individually.
Injector four (Bottom of the photo = rear of the bike) had a uniquely dry tip. The white residue was a bit puzzling. I peeked into cylinder four and maybe I saw surface corrosion on the intake valve  My gut tells me the O-ring stopped sealing a while ago




After some cleaning (hopefully I didn't damage the injectors) I tested them with a 9V battery. Two of them fail to spray or make sound when I close the circuit. (dumb mistake-- I did not keep track of which injector was which after cleaning) 
Here's what a good (?) one looked like as I push carb cleaner down a syringe


I think my options are 
1) buy good injectors to start the bike with
2) inspect or replace sparkplugs in the meantime
3) take apart the engine taube, before you spend more money

(I tried to look at the spark plugs tips, but I have to buy the socket. Also, the HT leads require absurd force to pull out. I could only get out #1 and #2. There's dirt outside but the contacts are clean.

Proper method for testing injectors recommends to measure the weight of gas they deliver.
You need 120gr. per minute with a 3 bar pressure.
If an injector does not deliver this, it's faulty.

First, I did not hear the fuel pump running in the video of the engine cranking.  Open the fuel filler and put the camera close to the opening when cranking so it can pick up the sound of the pump.

Do you have the tool kit for your bike?  There is a spark plug wrench in it.  If not, get a set of spark plugs and a plug wrench.  It is a tool you need.  If you don't have the factory tool kit, I would suggest going to Harbor Freight and getting a set of metric Allen wrenches, and a set of 3/8" drive metric sockets with a ratchet and several extensions.  along with some screwdrivers, pliers, and a set of metric combination wrenches you should be able to do most of the jobs on your bike.  All the tools you need should not cost more than $60.

The spark plug connectors are normally difficult to remove.  There is a metal tab on them that you can grip with a pair of pliers to pull the connector off.  The plug wires are marked with the cylinder they go to.  The #4 cylinder wire is longer than the #3 cylinder wire and is supposed to fold back.  If you cross them, the engine will not start or if it does, it will backfire and run very badly.

While you have it off the engine, it would be a good idea to soak the fuel rail in white vinegar over night to clean out any rust and dirt that may be in it.  Then blow it out with air or carb cleaner.  

I would suggest sending your injectors out to a shop that services fuel injectors.  From the way you describe them, it would probably be a waste of time to try to service them yourself.

Once you have new spark plugs, clean injectors, and can confirm the fuel pump runs you can proceed on to getting the engine running.

BTW, have you checked the crankcase breather hose and the rubber vacuum caps on the throttle bodies?  If they are cracked and leaking, they will make starting and idling very difficult among other problems.  If they need to be replaced it would save time to get them while the injectors are being serviced.

Point-Seven-five wrote:First, I did not hear the fuel pump running in the video of the engine cranking.  Open the fuel filler and put the camera close to the opening when cranking so it can pick up the sound of the pump.

You can hear a whine that continues for a moment after the bike stops cranking. I could be mistaken but I thought it was the fuel pump. In any case, there was fuel in the rail after a starting attempt. I'll confirm the pump is making noise with a closer look next time.

Point-Seven-five wrote:I would suggest sending your injectors out to a shop that services fuel injectors.  From the way you describe them, it would probably be a waste of time to try to service them yourself.

I think that's a good idea. I'm just worried about the two injectors that don't actuate at all. If the solenoid has failed, I don't think it's serviceable.

Point-Seven-five wrote:Once you have new spark plugs, clean injectors, and can confirm the fuel pump runs you can proceed on to getting the engine running.

BTW, have you checked the crankcase breather hose and the rubber vacuum caps on the throttle bodies?  If they are cracked and leaking, they will make starting and idling very difficult among other problems.  If they need to be replaced it would save time to get them while the injectors are being serviced.

I have not, but I will look into it whilst waiting for new injectors.

Thank you for your advice and suggestions, jbt and .75 

I replaced the fuel injectors. The fuel pump definitely sends fuel through them. The bike still won't start.

I will get new spark plugs and see if that does the trick.

The rubber vacuum caps need to be replaced, and I'll change the crankcase breather hose to be safe. 

The throttle body intake manifold look bad and I might need to change those too. This thread seems to be useful: 
https://www.k100-forum.com/t14821-clean-and-replace-throttle-bodies-and-plenum

Dont forget the vacuum pipe from no 4 to the fuel pressure regulator.

Also get yourself lots of spare injector seals. Those holes in the head will need to be cleaned and it does happen that you get a leak after refitting them....sometimes seal gets damaged in the process.

I removed old spark plugs for inspection. They look good, I think. I gently cleaned them off a little anyway. Re-installed, the engine still won't start and just cranks.




Can I run an '88 K100RS with D8EA spark plugs? I have four new ones I have yet to try because there's no "bobbin" (resistor?) cap  Word on the forums is the resistor is to prevent radio interference.

If it is a 2v engine it will run fine on NGK D8EA, I have run mine on them, sometimes D7EA and other times D8EA.

Do NOT use plugs with R in the code.

But you MUST have the bobbins. You will create all sorts of issues if you dont, destroy your plug leads, damage coils etc and bad running.

Check the Bosch plugs. Unless they are the moulded on type (really well done there, Bosch), a good twist with the pair of pliers should release the bobbins and you can then refit them to the D8EAs. Otherwise:-

https://www.ebay.co.uk/itm/404421262436

Yeah, I know! It's not much more expensive than buying just four and gives you lots of lee room to start losing them.

You will. Trust me.

What is the code on the Bosch plugs that you took out?

The old spark plugs were Bosch X5DC. The bobbin doesn't want to twist off. Thanks for the tips, I will get a cheap pack of terminal connectors so the NGK will fit.

You can also get the nuts from a small engine shop that works on lawn mowers and small tractors.  Those engines often have spark plugs with terminal nuts that can be removed and the shops that work on them almost always have some nuts or old plugs laying around.

I have a start!


The bike will only start if I open the throttle. Does not idle. 

Replacing the awfully cracked vacuum caps on the throttle bodies made a big difference, but I must still have a vacuum leak. I will next change the crankcase breather hose and the vacuum tube on #4