How can can I test the fuel pressure regulator on my K100 Rt? It still keeps juddering and I've double checked the fuel filter isnt blocked as I replaced it less than a 1000 miles ago as the air filter, and the filter on the end of the fuel pump.It ticks over and starts straight up but when riding it, it struggles to pull through the gears. Also done the exhaust and inlet valves and checked the throttle body rubbers for air leaks and balanced the same. Been all through the electrical connections and earthing points which all seem good. Starting to run out of ideas now?
Thanks Steve.

Hi Steve,

If you are a member of the BMW club (UK) they have a tool hire facility. In it is a fuel pressure gauge that can measure both the pump outlet pressure and that at the injectors to see of all is o.k.

Mike.

hi thanks for that

Steve,

The fuel pressure should be 36psi.  I am reliably informed that the fuel pumps we use in our bikes should be good for about 80psi, as they are taken from the car industry. 

If the fuel pressure is correct, then I would next be looking at the flow rate which would lead me to the fuel pump.  I am assuming you RT is a 1984. Is it the original pump or correct replacement?  I believe there was a change of pump around 1985. 

Also if the bike has had a few owners then POs could have played around with the airflow meter which may be giving you an incorrect fuel/air mixture.  As far as I know it should not be touched as it is set at the factory. 

I hope this helps.

TacKler.

HAve you checked the vacuum hose from the rear TB vacuum take-off back to the bottom of the FPR. If its kinked the engine will run a little rich on acceleration. If its split it'll be sucking air and the engine will be running lean. Pre '85 the vacuum hose did not have the spring hose protector installed on later models which prevents the hose from kinking. Yours is an '84. Just a thought. Worth checking.

Pic coutesy BlaKey

Another possibility could be missing or split TB vacuum blanking caps on the other
three TBs

Hi thanks for that, I have just another fuel pressure regulator and its no different and the vacuum hose looks good to me with no kinks, thought I'd solved it as for the first 300 yards or so it pulled nice and smoothly but soon as I came to a junction and moved off it was juddering as bad again. 
Thanks for the tips they are well appreciated. Regards Steve.

What condition are your spark plugs in? They could be faulty but can also give clues as to what's happening.

wonder if steve has checked the engine breather to plenum ...that s shaped hose that seems not to last for many

Hi again, The spark plugs are new D7's and the breather pipe is in good condition, Thanks for your help Regards Steve.

OK. Plugs might be new but what deposits do they have on them after running with the issue you have?
Oily, sooty, grey??? This will give you some idea about what's happening.

Thanks for this discussion. Attempting to beat the degrading (splitting) effect of heat over time on conventional rubber tubing I have fitted silicone rubber tubing. Any thoughts on this option? Have just purchased the spring to fit over the tubing to retain the integrity of the tubing inner when going round a sharpish bend. I suspect without the outer spring to retain airflow/vacuum where there are bends)the somewhat softer silicone tubing may be more prone to kinking and thus blocking inner tube. My aim is to have tubing with a clear internal passage when going round a bend and to be made of a material (silicone rubber) better able to cope with prolonged heat.

That silicone rubber tubing can collapse when it gets hot with vacuum applied.

Thanks for all your help and advice, I have now got it running spot on after I changed the injectors for another set. They sat loosish in the chamber and are now a tight fit, so they must have been drawing air in and that was the cause of my problems. Thanks again to everyone your a good bunch of people, Regards Steve.

Yep... that'd do it. You can get injector kits to replace the little filter, o-rings, spacer and pintle cap. They're pretty cheap. Also, all that gear gets replaced when you get the injectors professionally cleaned