Bought a 1983 K100 that has been sitting idle for a few years. Here is what we have done so far: 

I changed the oil and oil filter, drained the gas out of the tank, put in a new fuel filter, and put in a new Odyssey battery. The bike would turn over but it would not start. I can hear the fuel pump whirring loudly. A few times it could 'chug' once as if it was about to start but it didn't.

Then we changed the spark plugs but still nothing. We checked they were sparking and they were wet so it is getting fuel. We then took out the injectors and gave them a good clean. We cranked it when they were out to verify they were spraying ok. Putting everything back together - and then when we try to start it - it usually 'chugs' the first two but not much after that.

Today I did a few things like cleaning the ground and connections with electrical contact cleaner. Then we tried starting it while spraying "Easy Start" in the air box - and she fired right up. However then she died a few seconds later. We managed to do this a few times but it would not keep running. Once we heard a big of a bang and some smoke rose from the engine, not sure why.
Tried many times more, at one stage I was able to get it running without the Easy Start, on what seemed like incredibly low revs, it turned over for good few seconds just gurgling slowly, but then it would cut out.

So I'm guessing a fuel problem. Can anyone give me some pointers? Thanks

Sounds like a crap fuel pump to me. The flow back into the tank should be realy strong and put your thumb over the pump outlet and the pressure should be enough that you find it very hard to stop the flow
For a fuel pump go to Ebay for a Mapco 22301 it should be around 50 euro

Thanks Rick. Yes I had a feeling it might be this. How can I test that it is the fuel pump before I go ordering one?

It's very common for the fuel pump to be cactus after sitting for a few years.
Disconnect the fuel filter from tube that goes to the top of the pump and making sure to keep the it inside the tank so fuel doesn't spray put your finger/thumb over the end of the hose that comes from the pump and turn the key on and touch the starter button. The pump should run for 1.5 seconds and the pressure should be high enough to push your thumb away from the hose to let fuel out. (take care to prevent fuel spraying out of the tank) The fuel circulates very quickly and when you reconnect the fuel line the return of fuel to the tank should be almost as much as when the filter was disconnected. If that checks out OK then it's fairly safe to say the pump is OK. To check any further you need to use a pressure gauge connected into the system.

However, one small little thing. Check out the multi plug connector on the Fuel Injection Control Unit [FICU] under the seat. Clean off the contact pins and make sure that the plug is seating correctly. Its an easy job and known to create issues too. The 'start' as in turning over function relies on signal from the starter button which may be ok if you are getting fuel and wet plugs. But when it fires it relies on the signal from the Hall Effect Sensor. If that is absent then no start. This arrives to the FICU by way of that plug connector and if the connection is in any way off the signal can be disrupted. Been there. You can run the test on it after cleaning the pins without putting the FICU back into position but just by connecting the plug to it.

Also, try this.

Take your plugs out and clean. Then turn engine over a few times to blast out any old oil etc from cylinders. then replace and try again.

Every time I pick up a K bike that's been sitting for a while I don't even bother trying to start it until I've had the fuel injectors reconditioned. Have never had one fail to start after that. Gas dries out and turns into varnish if it sits for a while.

(Although I do agree that a stuck fuel pump may also be a likely culprit.)

He did say in his original post that he could hear the fuel pump whirring loudly. Whether this means it is working properly or not is not clear but fuel does seem to be getting thru.
So I think you might be right Duck, or something relating to this. I wonder if the fuel lines and rail were flushed when the tank was emptied? If not it may have been started on stale fuel and varnish and other gunk may have blocked the injectors right from the beginning. Also, stale fuel can cause valve damage in some circumstances.

I'd be checking the flow from the pump at the fuel rail then the return line from the FPR. Issues there would indicate a problem with pump, filter or FPR. If they're OK I'd then refurb the injectors with a thorough clean and new kits.

One thing I will add is that if you had a backfire which it sounds like the injectors can be dislodged from the hole DAMHIK so clean around them with carb cleaner and blow out the crap then remove the injectors and replace them using some pteroleum jelly to lube the O-rings.
NOTE If you dont clean around them the accumulated crap goes straight into the engine.

RicK G wrote:Sounds like a crap fuel pump to me. The flow back into the tank should be realy strong and put your thumb over the pump outlet and the pressure should be enough that you find it very hard to stop the flow
For a fuel pump go to Ebay for a Mapco 22301 it should be around 50 euro

Thanks, you were right. I disconnected the hose and there was no pressure in it. Ordered a new fuel pump so I'll fit it next week and hope that it starts then!
Thanks for the help everyone 

Keep fingers crossed you have it up and running soon. Do make sure you also check out that plug connector to the Fuel Injection Control Unit under the seat.

Will you be down for 88s Lecarrow Invitational and BBQ on Saturday 21st? Its not too far from you.

A few of us are planning camping over at Lecarrow Harbour on the Friday night. If that doesn't work for you looks like meet up point on Saturday morning will be at the Kilmartin's services at Athlone. Route takes us around the lake and back to Lecarrow Harbour for a BBQ.

Thanks a mil, sounds fun but I doubt I'll make it, bike is totally stripped and will be a while before its drivable again. Hopefully next time! I'll let you know how I get on with the Fuel pump!

I remember Will was going to France with me in 2014. At 1am he was putting a rear seal in his K. At 1pm same day he rolled up on it for lunch at Rosslare Harbour.............Not sure if he had leprechauns helping him along but he had sleep as well.

So the fuel pump arrived and we fit it tonight - and she started! So happy I finally got her running. Thanks for all the advice guys.

Only problem is she cuts out a bit the revs seem to dip - takes some fiddling with the choke to get it right. Also it can take a while to get her started. Probably not uncommon for a bike that's been off the road for a few years - but what should I do now to try to get her running properly?

I have a few videos I'll upload later

Some of the Ks can be a bit hard to start but you will find the sequence after a while. My K100 was very ornery and if I even breathed on the throttle it refused to start. Some times if you tap the start button so that the pump runs for its allocated 1.5 sec that will bring the fuel pressure up before you try to start it.
New spark plugs and a clean of the injectors will also help.

Thanks good to know. I have already changed the spark plugs. We also took out he injectors and gave them a scrub to remove any crap - sprayed them with carb cleaner. I was told to get a injectors spray and spray into the airbox. What else should I do to clean them?

Its the inside of the injector that needs cleaning. Use a 9 volt battery (the little square one in the smoke alarms) to hold the pintle open and squirt some carb cleaner in the top then remove the battery and leave it for an hour or so then repeat until the fluid coming out is clean. Probably need 2-3 times. Put new O-rings, filter in the top and pintle cap and you have a nice clean injector.

Maybe you should head down to Lecarrow for the meet up. I hear a rumour 88 can organise an ultrasonic injector clean for a few €.

If you check out the part nos they are also used in some of the BMW 6 cylinder engines and a set can be had from breakers at a good price.

Make sure though that the rough running isn't coming from perished rubbers on the intake.

Wohoo! I got her Started!     Thanks for all the advice guys. I cleaned the fuel injectors but she was still running a bit rough and cutting out. We started hunting around and I found the big pipe connecting the airbox was loose. Took it all apart and connected it up properly, she stared on the button and purs like a kitten! So relived. Really appreciate you all taking the time to help.

Now the real fun starts