Thunk on startup (and intermittent)!!

[Matt splat]

Hi guys, just finished cleaning the GSA after my poland trip, powerwashed it down yesterday, ACF-50'd it today. On startup (to burn off excess acf) i noticed a slight thunk just before the bike started. This is a new noise!

I thought nothing of it and have been letting the bike tickover, while just blipping the throttle there was a THUNK again. I stopped the bike immediatly. Started her up again, and got the thunk (not so loud as the running thunk) again. I let her tick over and i start blipping it again, nothing, BUT every now and then THUNK!

Anybody any ideas before i drive down to the dealers tomorrow?

Im thinking maybe the spring on the starter spline is knackered??

BTW (june) 07 GSA.

Ta. matt

 

[Dahoum]

from what area is the THUNK ?

 

[Matt splat]

Sounds like its from the front of the bike not been able to track it down yet, stopped for coffee and to pray its nothing serious

 

[Matt splat]

I dont think its the starter motor, it almost sounds like piston slap! It happens when the revs die to idle, then if i give it a blip it happens, only every now and then tho

Any idea's??

 

[terayon]

Seeing as you used a jetwash/powerwash, you might have got water into some of the ignition electrics, which might be giving you a bit of late or pre ignition as soon as you open the throttle.
See what it's like when the bike has dried out

 

[Matt splat]

Problem seems to be gone, she's running smooth as silk now, i must remember to be less liberal with the ACF-50!!

 

[Brian ROSEN]

I wonder if water could have been sucked into the cylinders after your power wash ? A small amount would have been enough - now it has been ejected and the 'thunk' has gone, hopefully without damage..

 

[jammyk]

same thing happened in norway

I had something similar. i traced it to two possible things.

1. starter motor not engaging cleanly
2. contaminated fuel caused (pre)ignition problems

running on UK fule that is clean the problem has gone. even starting with the clutch pulled in (like what you get taught on these new fangled off-road courses) doesnt replicate the problem.

if it comes back make a note of what you changed - i.e. fuel from different garage, just washed it (contaminated fuel/ignition) etc etc... usual testing ruleas apply.