Hi,

a couple of times recently I have gone to the bike turned the key and when I push the button, it fires up the petrol pump but not the starter motor. Also the pump keeps running rather than stopping after a few seconds.

The last two times this happened I fiddled with that fuses and after a few minutes it fired up and ran fine. I though it must be a bad contact on a fuse and waited for the next manifestation to carefully work out which one.

Today it dumped on me.

I was out of town shopping and it did the old routine but flat out refused to start. I poked and fiddled everything: no go.

Finally some kind sole gave me a lift across town and I manage to get friend to run me out to the bike to secure it and run me home.

Of course the damned thing started. OK at least I got it home.

Now I need to work out what the mystery fault is now it's not there to look at any more.


I initially thought of the pump being weak and not getting up to pressure: a pre-condition for the injection control unit to energise the starter IIRC.  However, I pulled off the feed to the injector ramp ; folded it back to seal it and could feel there was plenty of pressure. The pump was also straining against the pressure and making a different sound, so clearly it was getting higher than the pressure relief value normally allows.

This leads me to either suspect a wiring fault or the fuel pressure sensor or maybe the pressure release value is releasing too low. 

Anyone familiar with this problem?

TIA.

"a pre-condition for the injection control unit to energise the starter IIRC."
You don't recall corectly there is no fuel pressure sensor.

Yeah. I doubt it's anything to do with fuel supply. Most likely the starter relay or earth continuity thru your starter motor.
If you can hear the starter relay clicking when you press the starter button, then I'd be looking at the starter. Although it'svery possible for the relay to work but the contacts have been blown away. 
If the relay is not clicking then there are other issues.

OK, I think I was confusing the 1.5s hold on delay of the pump relay with the idea that it there was a pressure contact.

I can here the relay clicking so most likely seems worn brushes on the starter motor.

Ah, nice article from robmack

https://www.k100-forum.com/t2342-starter-motor-cleaning-tutorial

No. Simply remove the battery. Undo the power cable. undo the two mounting bolts. Pull it out straight and carefully  to minimise damage to the o-ring on the shaft.
Check for corrosion on the contact surfaces of the mounting bed because it earths to the GB casing there.
You can get the brushes easily or you can buy a kit with bearings, o-rings and brush set from EME for about US$29 + frt

Check for 12v on the starter cable when you press the starter button just to be sure you're getting power thru the relay.

It can take some effort to get the starter out too.

On my LT it came out easily just by 'sliding' it back towards the rear, but RT its a heck of a wriggle to do it but it will come, the only thing holding it is the O ring seal.

Comment on brushes is good but don't be tempted to clean off the commutator too much, just clean it with a cloth. Abrasive cleaning and it acts like sandpaper on the brushes. The 2 mounting points need to be clean with good electrical contact. You also have a single 10mm nut electrical connection which also needs to be a good electrical contact.

Before undoing the 2 long screws mark the end and cylinder points to line them up correctly. And then when you clean the outside as one is inclined to then you wish you had scratched the markings in the casing and not used marker. When it comes to reassembly the feeling I got was it was real easy but it seems it like if it goes together real easy its the wrong way round so make sure to have the markings.

Unfortunately Robmack's post on this is locked now, for some reason. :?

I had to use a tyre lever to hook onto a ridge where the end cover meets the body to get enough backwards force to get it to move. Obviously this needs to be done with some care so as not to force it off axis too much. The O-ring was fairly firmly stuck to the casing and although I could wiggle it there was not net movement backwards.

I found it needed some 'persuasion' to get it to come out and that removing the bracket with the coils gave better access to the starter motor body.

No way for the moment to know if this was the cause of the problem since like all intermittent faults, it only manifests at the most inconvenient moments, not when you are looking for it with the necessary tools at hand.

Anyway a bit routine maintenance and a check of the state of the brushes will either resolve it eliminate this as a possibility.

There is something about the commutator being worn resulting in a non start situation depending on where it has come to rest from the previous use. But this should still result in an audible click at the relay.

I doubt the commutator would wear so asymmetrically as to produce such a fault, however a defective winding could cause that. I don't think that is my case.

One of the brushes was particularly low and probably has little pressure on it. I've swapped in the starter from the other bike while I get replacement brushes. I'm going to upgrade the rather wimpy earth wire from the battery while I'm in there.

I have upgrades the power cables to the relay and starter as well as the earth and it made a big difference.

I now have an earth strap big enough to start a truck! 

Upgrading the rest is a good idea but it will have to wait, I need the bike.

Thanks to all above for help and comments.