In 2007 i had a Ducati M900 Monster- about 18,000 miles old but not the good early carb one or the fuel injected one ...
...a cheaper black 1997 model with those carbs that ice up, the dodgy fuel pump and the the reduced size inlet valves.
So i got some of the older large valve heads, ground in the valves, shimmed them, fitted the heads and serviced the Monster.
It was running smoothly and well at tickover and wide open but not in between. As is common on those engines the carburettor needles and jets were worn so i decided to strip and clean the carbs and fit a FactoryPro needle kit.
I had the carbs off on the bench and the bike in the middle of the garage about 3 metres away with the inlet stubs facing upwards (but not covered = Mistake 1
I stripped and cleaned the carbs, installed the parts and started the rebuild... all so good so far. But as i tried to get the two carbs throttle spindles to engage the little spring that tensions that engagement said Bye Bye! and jumped.
..cant have gone far... (= Mistake 2
I spent ages with a torch and magnet looking for it on the bench then the floor (= Mistake 3
)- no luck.
I checked my bits-tins for a replacement - no luck
Then i spent a couple of hours on-line checking carb and spring specialists for a replacement - no luck
So i stripped every biro in the house and shortened the most similar looking spring to fit.
Carbs back together - all looking good
So i fitted the rebuilt carbs - it was a pig to start on one cylinder but I assumed it was just due to empty float bowls. The throttles did not synchronise at all well so i took it out for a ride to see if it would settle down. The mid range was better but starting was really poor, top end was soft and tick over was sh1te everything apart from the pick-up was worse than before the carb rebuild.
and next morning decided i needed to go back to basics & check everything.
So into the garage and started with the last thing i had touched...stripped and rebuilt the carbs again but the carbs fuel lines, fuel pump etc all looked fine.
So i decided to to check through all of the things i hadn't touched
(or thought i hadn't
About an hour later i was down to looking at the valve clearances...
And then i found a big (about 0.050") clearance on one of the inlets
...Much swearing ensued
I took off my nice 'new' cylinder head and sure enough i found a bent inlet valve!
A valve with little scratch marks on the valve edge, a line dent in the valve seat and little pock marks on the aluminium of the cylinder head. No other evidence or marks anywhere - a valve that had been sealing 24hr before was now bent
As far as i can tell that Bl**dy spring jumped about 3m then accurately fell down a 40mm inlet stub, caught between the open valve and the seat and as the desmo cam heaved the valve shut it bent... the spring then came loose and bounced around inside the head before finding the exhaust port
Cost total: about 10 hr work, 1 week riding time, 1 new inlet valve, 2 more closing and one opening shims to get the new valve clearances and another gasket set.
Btw - My tips ....(1) don't ever leave inlet ports unplugged
(2) biro springs are great