holed piston :( so angry (now with pics)

[Adam_Winstone]

To double quote a couple of you already...

"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"

I had plenty of time to watch my EGT on the motorway in France for the recent Euro and I noted a couple of times that the temp started to creep up and was getting worryingly high... then the bike would go onto reserve! Flicking onto reserve would keep the bike going and I would then see the EGT readings slowly drop again. This did confirm that getting close to reserve will lean the bike out and make it run hotter but it certainly didn't cause me to suddenly put a hole in the piston. Perhaps this is because I run with a somewhat wider safety margin but I imagine that a motor would have to already be on the weak/hot side of normal for this to put the final nail in the coffin.

Adam

Edit: Perhaps this becomes more of an issue with a long-range tank, where you are nearly on reserve for a longer period (based on surface area of fuel dropping)?

[tonydevon]

the 300 float valve is in the 26mm carb now, been right thru the carb and all fine, going to up the main a bit, cam lam mentioned when I called them about a piston that the AV266 might be a bit lean, so will try a AV268, as well as knocking the timing a degree

dont mind losing some power,

but cam lam also said that this happening is the reason that they sell the taps with warning lights instead of reserve tap.

nobody seems to believe me that it came out of nowhere, oh well such is life, hopefully have it back up and running in a few weeks.

without this forum it probably would have been sat in the middle of my carpark with people round it toasting marshmallows on it

[tonydevon]

yes I have a 14.5l tank, but Im also thinking that my riding style needs tweaking, I had been riding quick then was behind a car downhill on a section of road with double white lines, just rolled off the throttle and cruised along behind it, Im thinking that this next to no throttle travelling might have raised the heat, this then compounded by running out at full throttle once the car had turned off the road.

I assume that being on the overrun theres no fuel going into the barrel?

Im used to 4 strokes, not ridden 2 strokes for about 20 years, even then it was watercooled stuff,

[sean brady scooters]

yes its very important i think and advisable to dip the clutch and blip the throttle often when coasting ,especially after hard faster riding ..suddenly shutting off the throttle starves the engine of much needed cooling fuel exactly when it needs it.

[dapper]

yes its very important i think and advisable to dip the clutch and blip the throttle often when coasting ,especially after hard faster riding ..suddenly shutting off the throttle starves the engine of much needed cooling fuel exactly when it needs it.

I typed up a similar response when I read that it happened on a hill, but must have forgot to hit submit

[sean brady scooters]

you also have to envisage what happens at the point of going onto reserve ,not only does the fuel flow cease suddenly but also air gets in ,not good !.
again I always prefer( and advise folk ) to ride scoots only ever on the reserve position in order to prevent that scenario .

[Donnie]

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)

Well to me that translates as you were set up lean when on full throttle, which is when you said the problem happened :-/

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

so, likely running lean all that time and starting to weaken the piston crown

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.

Probably because you never got into main jet area, ie were mainly in the needle / slide / atomiser

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)

Nope, to me it looks now like you were running lean all the time on main, the 9 plug may well have kept the temp down a bit but I bet there was already a degree of damage on the piston crown at that stage. Then after using the 8 and your latest caning it was enough of running lean to finally pop the crown. I bet it running beautifully just before it want pop too

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 one of the joys AND FRUSTRATIONS of running an alloy barrel. If you had tried running an iron barrel with the same settings then it would quickly have given you the feedback that also gives you a warning that something is up; a seizure. However, the alloy kits shift so much heat that they don't seize, even when running very hot (for whatever reason), and keep running, and running, until POP!, you hole your piston. For this reason, whilst you may get away with more margin for error with an alloy kit, you may not have any indication (or small signs that you may not pick up on) that there is a problem before it goes wrong.

An iron barrel quickly tells you if something is wrong, whereas an alloy kit may only whisper it.

Adam

[tonydevon]

well the pop was audible LOL

I heard that ok, and my wallet heard the price of the new piston

to be honest I maybe should have started with more of a standard engine, than building this one as my very first scooter.

however this lesson is learnt, wont do that again, but some other mistake will be waiting in the wings

[Doom Patrol]

An iron barrel quickly tells you if something is wrong, whereas an alloy kit may only whisper it.

Adam

Yep! Back to cast. You just don't have the feel with an alloy barrel.