I've owned and ridden my bike since last March 2020 and have only put about 1,500 miles on the clock, previous owner had told me that he'd done a full service and ridden her back from Heinsberg in Germany at the end of January 2020.
So my bike was in storage for 6 weeks over the winter,dry and cool lockup.
 She started up first time when I took her out , rode her home , rod her her around for a week, refuelled her and rode 8 miles parked up at a friends for a cuppa, came out 3 hours later... started straight away... 300 yards down the road the revs dropped , I dropped a gear, revs still dropping, dropped into 3rd ... then 2nd throttle wide up ... bike is kangarooing down the street with erratic revs...managed to get home 3 miles.
went online checked here and other places for symptoms....  
decided to check air/ fuel/ electrics ....problems I found  
* spark plug 1 showed soot
* Spark plug 2 plug cap was damaged not connected to spark plug
* Spark plug 3 wet unburned fuel
* Air filter was grey with muck


I replaced all the Spark plugs ,  3 of the Spark plug caps and the air filter 

fired her up and ran nicely ....... went out yesterday battery flat... battery on charge overnight , wouldn't turn over today... hooked her up to spare battery... started and the problem is back  ... any suggestions ?
 
 i've put a link to a video of  what she sounds like  .... during the video the rev surges and drops are not me over revving the throttle

https://drive.google.com/file/d/1ygBt9YAj2iyiwDLspKxgwqCfHw6TBPyv/view?usp=sharing

WayneD wrote:. . .  previous owner had told me that he'd done a full service and ridden her back from Heinsberg in Germany at the end of January 2020.
* Air filter was grey with muck

The condition of the air filter contradicts the owner's assertions. Check the fuel filter to see if it's clogged. Check the tank's interior fuel lines to determine if they're loose or deteriorating. Verify that the Jetronic plug is tightly seated. Verify that the battery's ground connection is clean and tight on the transmission. Check the condition of the z-hose connection from the crankcase to the air box. Maybe you'll get lucky by addressing only these conditions.

Laitch wrote:

WayneD wrote:. . .  previous owner had told me that he'd done a full service and ridden her back from Heinsberg in Germany at the end of January 2020.
* Air filter was grey with muck

The condition of the air filter contradicts the owner's assertions. Check the fuel filter to see if it's clogged. Check the tank's interior fuel lines to determine if they're loose or deteriorating. Verify that the Jetronic plug is tightly seated. Verify that the battery's ground connection is clean and tight on the transmission. Check the condition of the z-hose connection from the crankcase to the air box. Maybe you'll get lucky by addressing only these conditions.

thanks for the suggestions, I've been and checked  what you mentioned and also replaced the fuel filter in the tank .. but I'm still getting the same problem.

You might have condensation in the tank from its storage time, especially if the tank was low. It might work if you lean it to the right so the water goes away from the pump.

WayneD wrote:thanks for the suggestions, I've checked  what you mentioned and also replaced the fuel filter in the tank .. but I'm still getting the same problem.

It looks like you're crossing into bad luck territory. Tell us what else you have investigated to remedy this condition.

Laitch wrote:

WayneD wrote:thanks for the suggestions, I've checked  what you mentioned and also replaced the fuel filter in the tank .. but I'm still getting the same problem.

It looks like you're crossing into bad luck territory. Tell us what else you have investigated to remedy this condition.

so after much fiddling i took out the fuel pump while bench testing it I realised it was making a 'squeeling' sound... ordered and fitted a new fuel pump... problem solved.
 out of curiosity I opened the old pump and found the inside 'gunked' up with a brown grey sludge that smelt of petrol and burning rubber and appeared to be stopping the fuel from passing through.. showed it to a local mechanic who said he thinks its a dissolved  seal possibly caused by ethanol in the petrol

The ethanol does that to the damper mounting, right diagnosis!. Did you replace it?

92KK 84WW Olaf wrote:The ethanol does that to the damper mounting, right diagnosis!. Did you replace it?

Yes , I replaced the black  fuel pump mount with a silicone one I 'found' on ebay