the Post Mortem on Purple PD
OK - you asked for the outcome of Rob's findings-
On the ride over to Rob's, from Cambridge, the revs had started sticking at around 3000 rpm, and not dropping back to a normal tickover. We all know what causes that ! Not a major showstopper as far as getting to Rob's was concerned, but certainly a bit of a problem on wet roundabouts- riding without engine braking or proper deceleration is ,at least, interesting ! Whilst stopped at traffic lights in quiet Melton Mowbray, engine was screaming a bit, so switched off, and restarted as the lights changed to "Go" -there was a loud backfire, that must have woken up a few locals having a Saturday lie in !!
So, first thing we did when I arrived at Rob's was to swap out the beancan for one off his GS, re balance carbs and adjust timing, and problem of over revving was sorted- ergo - beancan was 1 problem.
Inspected my beancan, and it looked remarkably clean and tidy, and bob-weights seemed to spring back just fine, so no obvious smoking gun.
However, it is just possible to grease the pin the weights swivel on, so Rob did that, as well as clearing slight amount of gunge on one weight.
Re-fitted to the bike, adjusted timing and carbs again, and straight away sounded and responded much better, tickover was able to be set more accurately etc., -so clearly must have been sticking, despite looking clean. (The bike is in pretty clean condition overall, as well as being low mileage.)
Next job was to remove the ridiculous "Secondary Circulation System" bits;
this involved blanking off the exhaust exit point under the front pipes, replacing the original airbox with a non- SCS one, and fitting screws to the vacuum take-off vents on the carbs. Bits were provided by
MotorWorks and cost grand total of about £26. The exhaust take -off point on one side was fairly loose, so just possible that air was getting drawn in, or causing whole stupid SCS to malfunction, but this was never definitively established.
Took bike for a quick warm up and run, and already huge improvement- no over revving , no lovely backfires
, and smooth tickover. But there was still slight surging , but nothing like the previous kangaroo hops I had before.
So, we then removed carbs, Ultrasonic cleaned, although main jets appeared pretty clean, there was slight accumulation of grime, but nothing too severe.
Carbs were blown through with the airline, and replaced and re-balanced etc.
Ride home was a whole different experience to the morning's careful ride- bike pulled smoothly, and absolutely no signs of surging, accelerated better than ever, and sat at 85-90 ( on the M1/A14 of course
) with no problems. Tickover was sitting steady at around 1000 rpm. A different bike ( but still Purple though.)
So, big thank you to Rob- couldn't have been more helpful , even with his dodgy groin! I'm much relieved now, and it all goes to remind me what , to me at least, this UK GSers site is all about. People offering the benefits of their accumulated wisdom, help, expertise, and not least, time.
I would have been lost without it
I hope the above info on this post has been of help and/or interest to others who might have similar problems, and very happy to pass this on, and report a successful outcome.
