Now we see the same problem time and time again coming through the workshop, especially in spring when people get their bikes out after a long storage… and that time is (nearly) upon us.
The fuel left in has turned to varnish in the carbs or injectors, clogging them completely. They need stripping and cleaning; typically, when stood one carb or injector will have less fuel in it than the others, and as it dries out the residue gums everything up.
For older bikes, in extreme cases you’ll need a new bank of carbs, and it’s not the jets or needles that are the problem but the air bypasses in the cast body; once they’re blocked, it’s game over.
Petrol these days is effectively useless after two months so the best thing you can do is use a product by Silkolene called Pro FST – it’s a fuel additive that will stop petrol deteriorating. For everyday running you add a very small amount – 1-2% – but prior to laying up the bike put about 500ml into a full tank and run it through to make sure it’s in the carbs or injectors. It’s much cheaper than a carb or injector strip and clean, trust us… just ask the owner of this track day Ducati 998S!
The Ducati 749S below is owned by a customer who’s been coming to us for several years. It’d been parked up for a while but he dragged it out wanting to use it but found it suffering with a load of running problems – holding back, misfiring, general lack of power etc.
And it’s the thing we see a lot of; the fuel pump, fuel filter and everything connected was clogged up with the gunky remains of what was unleaded. The bike was in for a normal service, which we did first, but then we had to strip out the fuel pump, clean it and change the fuel filter, but with only partial success.
With a pressure gauge attached the fuel pump was found to be lacking – just plain knackered, so we sourced a replacement and slotted it in. Bingo! The bike’s now running better than ever. Pro FST in the tank would have avoided the problem…
- Cleaning the fuel pump an filter helped this 749’s poor running – replacing the fuel filter made it perfect…