hey guys, This is my first post here, after my introduction! I have a 1985 k100rs, and I'm looking for a second opinion...

Last week, I went out to my bike early in the morning and it wouldnt start. Normally I need to put the choke on to get my bike going (even when its hot out), but today nothing was working. Later that day I push started it with a friend and got it going. For the next few days, the starter wasn't working. Not sure if its the battery, or the starter, or what. Anyway, I had to park on hills and push start every time. One day i pushed start it at a low speed in a small area, and it turned on, but i didnt give it enough gas, and it died. 

Since then, I haven't been able to get the bike on, even when push starting. i've tried multiple huge hills. My assumption at first was something electrical, but now I'm leaning towards fuel. when i try to push start it, it just sort of grumbles and skids to a stop. Also, I can get the bike to fire up if i spray carb cleaner into the air box.


i'm guessing the fuel pump. 

I'm getting horrible mileage out of the bike. Someone yesterday said it sounds like my fuel pump is out, and that now i'll need to adjust the valves, which are probably out of wack from puel pump being out for so long. fuel pump could also explain why I need choke on to start bike. Also, a few weeks ago I was changing the fuel filter and when I removed the tank cover, a ton of debris fell into the tank, and I couldn't get some of it out.

What do you guys think? The bike has plenty of other problems, so maybe im overlooking some other tell tale signs.

Thanks guys!
Ben

First test is When you push the start button does the fuel pump run, it should run for 1.5 seconds after the start button is released or if the engine is going it will continue to run.
I would suspect that this is where the problem lies so do that check then if it doesnt run check the plug where the electricals attach to the tank, that plug is a very common source of trouble. Also check that the plug on the ECU is seated properly, it is below the tool tray under the seat.

There is a very good flow chart available for troubleshooting a no start situation on the downloads page but you will need to contact Crazy Frog (our admin) to get initial access.

If you want a manual send me a PM and I will send a link to you.

Hi Ben, after reading your description I'm left with the feeling you're guessing or grasping at straws.  Better to be methodical and do some testing, starting with the common problems that often crop up on these old bikes.  When you say the bike will not start, you don't mention if the starter itself is working or not.  Is the engine turning over but not firing?  Have you measured the battery?  Did a load test?
If you found swarf and bits of black stuff in the tank, you'll be needing to remove the tanks and give it a good flushing.  The rubber cuff that holds the fuel pump can disintegrate in time and contaminate the fuel.  Once the pump ingests some of that stuff, it's pretty much curtails. New pump time.  Fortunately, there are lots of non-OEM options.  Have a look on ebay now and you'll find a pump that is about the equivalent of a good lunch, price wise. 
Tell us some of the details of the problems you're seeing and suggestions can be more on point to help you get the old girl back where she belongs -- on the road!

A quick test to see if the pump is working is to lightly squeeze the fuel pipe that feeds the injector rail. If the pump is working you'll be able to feel the pressure in the pipe.

Paul.

I have a similar problem and inside my tank is clean as a whistle. Even better I drained it off a few weeks back.

I checked and eliminated the tank plug connector and also the connection under the seat, as Rick G says well known trouble areas. 

I have the diagnosis down to pump and/or filter and about to do one test. Suggestions are to run the pump backwards/reverse to unblock it, as a bench test but I figure why not do that in tank..... Not sure this will work but the fuel pump is 'running' as it makes the normal whine, only no fire and no return fuel moving around inside the tank [I tried it with the tank open].

So being too busy just now but wanting bike back ASAP, I would prefer do this without pulling it all apart and without draining the tank which is almost full......I checked my spares bike and see I have a perfectly good tank connector and was going to remove it with a certain amount of wire. The object being to plug it into the tank socket, in place of the normal one, then connect a battery with the terminals reversed so it will run backwards inside the tank.... Ok, its got 4 wires of which I assume the 1 brown is an earth, 1 is for the 7 litre warning and 1 for the 4 litre warning and 1 for the fuel pump. So which of the other 3 powers the pump......?

Not going to do any more for now, ordered one of MotorbikeMike's pumps off eBay this evening and if reversing the polarity doesn't work I will fit that with a new filter.