Let me explain:

The outfit hasn't been running too sweetly of late, getting progressively worse. Rough at low engine speeds but seemingly OK above 
3000 rpm.

I suspected the AFM, maybe a sticking flap, but changing it made no difference.

Last Friday I realised that it was running very rich and, remembering posts about this topic, I used the search facility to find references to 'RICH MIXTURE'.

A good read came up with many ideas, but Krambo's thread seemed to match my problem perfectly, with the following suggestions.

So, 3 possibilities, fuel pump, fuel pressure regulator or a blockage in the return feed to the tank.

Using Bert's (Crazy Frog) excellent 'Trouble Shooting Guide', I connected a pressure gauge to the fuel rail via a tee piece......WOW pressure off the scale! 

Next, check the pressure coming from the fuel pump........again off the scale. I used the tank off the solo to confirm that the FPR was still functioning correctly and hadn't suffered from the excessive pressure. Yes, we all need at least 2 K's  

The conclusion was, therefore, a duff pressure relief valve in the fuel pump.

Today the new pump arrived and, after resetting the bypass screws (I had tried to get a decent tickover with the fault, so they were way out), all is back to normal. 

So, you see, without this FORUM I, and probably many others, would be struggling to keep my bikes running.

Hence a big THANK YOU!


Paul.

Glad to hear it, Paul. Did you use an OEM replacement?

No, Kyle, I put the substitute pump in a separate thread so that it will be easier for anyone to find at a later date.

Paul.

Just saw it. Love to find a US counterpart for that price.

That's a good price (referring to the eBay link on the other post)! In the USA, check EME's price on a new Enduralast fuel pump. With the exchange rate from Pounds to USD from the eBay site, £48.95 plus £22.00 postage = £71.00, that's equivalent (today) to USD$111. EME has one for $129 plus postage or $112 for a replacement 'kit' which includes ancillaries. And no extra waiting for the Royal Mail parcel to arrive at your door from the UK. The deals are out there if one knows where to look.

Enter Here Then Scroll Down

sidecar paul wrote:
The conclusion was, therefore, a duff pressure relief valve in the fuel pump.

You just give me a wonderful idea
Never thought of that, got 2 K75 with fuelproblems.
(What "we all must have at least 2 K's".....)
Heaters up, shedman is coming

Two Wheels Better wrote:Enter Here Then Scroll Down

Thanks TWB. EME's a great shop, too.

great solve paul

would never have thought of that, without the forum

cheers and great news that contributions have rewarded in a solve ...yet again ...

cheers from down here

Paul,

Using Bert's (Crazy Frog) excellent 'Trouble Shooting Guide', I connected a pressure gauge to the fuel rail via a tee piece......WOW pressure off the scale!   

Was that where you would have expected 32 psi? If so would that not point to the regulator not dumping the excess back to the tank?

Mike

No, its indicating that the fuel pressure regulator doesn't allow any fuel to return to the tank. Therefore you'll be seeing the max pressure the pump can generate until its build-in safety blows

Mike, as I see it, the pressure at the fuel rail should be maintained at 36 PSI by the FPR, with the pump supplying at 65 PSI, so a
 tee-piece to a pressure gauge from the fuel rail should read 36 PSI.

 Now, if the pump pressure relief valve isn't working and the pump is supplying around 160 PSI, the FPR can't allow enough fuel to pass to reduce the fuel rail pressure to the required 36 PSI, hence the high pressure reading.

Paul.

This forum is getting to be a great database on knowledge thanks to people like you who post their findings. Well done, nice result!

Team, there's a difference between pressure and delivery volume with a pump. I doubt that the pump can bring up enough pressure at volume if the FPR is fully open.

ReneZ wrote:Team, there's a difference between pressure and delivery volume with a pump. I doubt that the pump can bring up enough pressure at volume if the FPR is fully open.

Thank you, Rene. Getting a bit confuzzled there...

Opinion please. I've installed 4-hole injectors. Love them. After reading thru the posting re pressure levels for 2-hole vs. 4-hole and the possible drop in injector efficiency (Thanks Capt. Hollister) I am considering an aftermarket adjustable FPR (ref. this) to dial in a bit more pressure for the 4-holers. 

Thanks in advance.

It seems that I was a bit premature with my report of success as, on the first ride, the richness reappeared after a short distance. Returning home I found that I was still getting an excess pressure at the fuel rail. 

The only other item in the chain is the fuel pressure regulator, so I bought and fitted a new one and, bingo, after a short 30 mile hop last night things are now really back to normal.

On reflection, considering some of my hasty conclusions, I can't see how a simple spring loaded pressure relief valve on the fuel pump could fail, but I did see a high reading on the pressure gauge when connected to the output. Anyway, a new fuel pump after 28 years use is probably no bad thing. 

Last night, discussing all this with a friend who used to work with fuel systems, he said he was surprised that a Bosch FPR, being quite a simple bit of kit, could fail causing a blockage. The more likely failures would leave a free flow or, with a ruptured diaphragm, dumping fuel into the manifold via the vacuum hose. So he urged me to take the old one apart.

This morning I turned off the flange and here's what's inside a FPR.



That flat valve should be captive in it's housing, but with wear on the ball and on the plate that holds it in place, it was able to escape!



So, it would seem that the diaphragm was moving backwards under fuel pressure but leaving the valve behind to block the output port.

Well, at least I now know what's inside a FPR and in spite of a few blind alleys, I've got to the bottom of the problem.

I suppose a modern engine would probably have a sensor on the fuel rail which would shut down the 'computer' when over pressure is detected requiring a visit to your dealer! It's a tribute to the K design that it still runs with such a fault which makes it possible to (eventually) diagnose.

Paul.

wouldn't be the first time we have seen intermittency on the failure  paul

interesting to see the internals

cheers

Good one and thanks for posting the pictures, good knowing how it looks like and what possible fails might come from it!