holed piston :( so angry (now with pics)

[Donnie]

Hopefully someone better than me knowledge wise will be able to comment but a 102 main jet seems a bit low to me for your setup???

[Speed Demon]

You can chase every possible scenario listed in this thread but the symptoms you describe immediately before the failure are still fuel starvation - if it went onto reserve at full bore then that will do it.

You can do as many plug chops, re-jets and leak down tests as you like but if the carb isn't getting any fuel from the tank then it will hole a piston. With no supply it will go lean even with the biggest main jet in Christendom fitted.

[tonydevon]

now thats the answer I wanted to see, feel like Im trying to tie knots with mist, cant see any reasons for the failure

but keep being told that it cant have been "just" because I ran out of fuel, so Im chasing other problems that might not even exist

it went onto reserve at same time as I reached base of the hill whilst full chat, so guessing that it dropped away from the tap as well, I didnt immediately realise what the problem was, knocked the tap by foot to reserve, but while waiting for recovery I noticed the tap wasnt fully downwards, maybe I knocked it enough to get some fuel through, but not enough???

if I can afford to get it back together then Im going to leave it on reserve and be more careful and pay attention to the mileage and keep it full. expensive sickening baptism into scooters LOL

[shocky]

just a thought it is actually a 2t carb you have and not a 4t one and 102 seems way low i would have thought a 122 more like it

[shocky]

now thats the answer I wanted to see, feel like Im trying to tie knots with mist, cant see any reasons for the failure

but keep being told that it cant have been "just" because I ran out of fuel, so Im chasing other problems that might not even exist

it went onto reserve at same time as I reached base of the hill whilst full chat, so guessing that it dropped away from the tap as well, I didnt immediately realise what the problem was, knocked the tap by foot to reserve, but while waiting for recovery I noticed the tap wasnt fully downwards, maybe I knocked it enough to get some fuel through, but not enough???

if I can afford to get it back together then Im going to leave it on reserve and be more careful and pay attention to the mileage and keep it full. expensive sickening baptism into scooters LOL

maybe an EGT MIGHT have alerted you to the problem before it got critical

[Darrell Taylor]

as sticky says beware the "switching on to reserve" as the float/fuel level drops it gets leaner for a long enough time to seize/hole before the motor tells you its out of fuel

c.s.i lambretta! heres quite a few checks i like to do pre dyno or after a failure ,you eventually find a problem or 2/3/4

good to try the fuel flow test thru the carbs needle valve ,remove the bolt on float bowl holding it in place and measure as normal flow,check
check the casting hole under the filter is clear as well as filter
check needle valve is 300+
if the carb has a surge baffle plate check its not slid up too far and reducing float height/check float heigt too
check carb body for signs of rubbing on parts of the scoot or engine as vibration froths fuel and runs lean
the fuel tap orientation on the lever needs checking for correct position as on is somtimes 1/4 on due to baggy universal joint
check tank fuel tap isnt touching down and vibrating
check fuel lines arent kinked or trapped with someone or 2 sat on the scoot
check tank cap is breathing
check tap fuel filter isnt blocked
check fuel for oil
check fuel for water droplets
check pilot jet for blockage
check rubber for splits
check inlet manifold faces for sealing youll see wet patches if leaking
check base gasket surfaces again wet patches
check head gasket for leaks(pics look fine)
when reassembled leakdown test(best done before stripping as saves a few of above checks)
add some more checks later lunchbreak over now

[tonydevon]

thanks guys, Im feeling more confident, at least the opinions of the experts is that it "is possible" that it occured purely due to my stupidity of running out of fuel. but obviously not 100% certain

as I understand it the jetting was done to be mainly on the needle for midrange and to make it safe, this overlapping the main hence the smaller size?? (as I say thats just my understanding)

all I can say is that only a couple of weeks previous I had it pinned WOT for quite a while on way to Newquay, was caught up with some slow riding bikes and decided to try and have some fun, riding like I was Rossi LOL

certainly didnt hold back on the throttle and it just went and went, never complained, ride back home 2 days later was slower and more sedate due to club scooters being slower, but again it was fine.

this is what confused me so much, as I had thought that if it was going to blow due to setup, then it would have during the 65 miles of A road caning (had an iridium 9 plug in for that ride)

I thik a few changes are due for it if I can fix it and get it back running, wassel conversion, so I can fit a battery and then fit EGT guage thingy in legshield box. while I seriously pee'd off, the barrel has survived, so in the grand scheme of things maybe I got lucky, perhaps its time to get some "insurance" in the form of modern technology to try and help it not happen again

[Adam_Winstone]

This is identical to the over advanced timing hole in my mate's correctly jetted Mallossi 210. However, what you want to do is slightly adjust all the factors that can cause this, so being pretty sure that you resolve it and it doesn't happen again. As such, you want to go lightly richer on jetting, slightly cooler on ignition timing (retard it to 16 degrees or less), and with compression like that be sure to run a 9 plug at all times.

I'm really chuffed for you that the plating looks ok. Close shave!

[bristolmod]

Glad you're feeling a bit happier about it Tony, and you haven't taken a hammer to the rest of the bike.

As an aside, when they blow like this, doesn't the engine sound lovely and smooth as you coast onto the hard shoulder!!

Hope you get it sorted.

Chris

[ktmh5]

just a thought it is actually a 2t carb you have and not a 4t one and 102 seems way low i would have thought a 122 more like it

I agree that a 102 sounds low but it is only a 26mm carb Shocky and not a 30mm. I thought about a 105 would be about right. I would also try an x7 needle and a 300 float valve.