Hi, Conman, sorry about the delayed reply, I've only just spotted your post. I can, in no way, claim to be an expert but I have experienced the same problem as you when a friend was restoring our Yamaha RXS100 that had stood in the garage for 6 years on a SORN. My friend described the deposits in the carb as 'a varnish' and, via a contact, successfully cleaned it out using ultrasound; I'm sure that it would be well-worth you trying it. I understand that the deposit is caused by additives in unleaded petrol.

I also recall that the fuel tank needed a thorough cleaning out, though I can't remember if this was due to the 'varnish' or simply rust that had formed inside the tank.

Good luck - let us know how you get on with the Adventurer.

Sadly, the Yamaha is again awaiting restoration/rebuild following just 3 months on the road, after which it was t-boned and written off by an impatient twerp in an Audi.

Hi well back again.

well I stripped the carbs down again and found one of the pilot jets blocked. Cleaned all carbs again, still found little bits of s--t lying around but hardly any, on closer inspection of the tank found it rusty, so treated it to a PQR 15 lining treatment. It is done in three steps.

1/ marine clean that does as it says, I couldn't believe the amout of gunge that came out,

2/pre paint treatment, this treats rust etc.

3/paint. it stresses not to rush this stage and make sure the tank is thoughly dry before hand. luckly I had a snake scope to enable me to see some of the inside and on two occasions when I thought it should be dry on closer inspection it wasn't. 8 days I left it in all. now all is perfect tank wise .

when I started her up finally, with a bit of carb balancing and pilot jet adjustment she now runs as sweet as she did when she was new, I have put an inline petrol filter just incase and getting back to my original question should I buy or use a ultrasound cleaner. my answer would be no, but I would get some PQR 15 marine clean as that seemed to dissolve the 'varnish'. You bet.

Hi, I had the same problem with my 1993 Triumph Sprint after it was stood for only 3 months. A flushing with a good quality fuel additive followed by a tank of non-ethylene fuel cleared it

Turned out to be ethylene coming out of the mix and depositing itself. This is a real problem for the small bore jets, injectors and fuelways on motorcycles. Not to mention the devastating effect on plastic fuel tanks, for some makes.

In the Uk, there is now 5% ethylene in our pump fuel and it seems this might well increase in the near future. Doesn't bode well.

AndyB