Another Holed imola Piston....AAaargh

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nellyboyo
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Fri Sep 27, 2013 4:33 pm

Bit of a story this one....Got a suspect tanks of petrol a while ago, lots of grit and sand in it, blocked the main jet, blocked the needle jet twice all in the space of a few miles.....Had plug out when cleaning the cab out at the side of the road and it was perfect. . Two miles later holed the piston suddenly , heard it pink then bang......Right , drained the tank though a pair of tights, refilled it through a pair of tights again. Fitted new piston and gaskets, had 2 small fill ups from different stations ...80 miles later ....after taking my time ......pink..bang .... When I pulled over the carb was overflowing like the needle jet was stuck .
That`s the bit that`s confusing me ?? I thought it would get too much petrol of the needle was blocked and bog down or something ...I've ordered a new piston and I cant trust my carb anymore
This is getting expensive now...

mick1
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Fri Sep 27, 2013 4:37 pm

Possible air leak.......what's your timing set at ? maybe worth a check

nellyboyo
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Fri Sep 27, 2013 5:09 pm

Don`t think its an air leak as it hasn't been racing or anything .....timing set at 18 deg...if it was overflowing out the carb does it mean the barrel wasn't getting fresh charge at that same instant ?

dave wheeler
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Fri Sep 27, 2013 5:34 pm

still s**t in the system, so as well as a non sealing needle you`ll probably find blocked jets, change the tap, change fuel, check fuel flow through tap, check stickys manual for safe flow rate, THOROUGHLY clean carb and you should be back to where you started

Adam_Winstone
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Fri Sep 27, 2013 6:00 pm

Could be 1 of many possiblle factors, however, I'd start by setting the ignition timing to 16 dbtdc as 18 seems pretty high to me, unless you have a very low compression head. Any idea what your compression ratio is?

Also, which version of the Imola is it? The different versions of Tino's kits seem to vary considerably from one generation to the next so it is not a good thing to mix and match components or set-up suggestions. Please note that this is not intended to fault the continued development of the kit, just a reminder that you need to ensure that head/compression is suitable for the exhaust port height and corrected compression rate... with a holed piston often being the result of getting this wrong with an over advanced ignition setting.

Good kits with excellent performance and reliability, providing that they are set up correctly.

Best of luck with it.

Adam

nellyboyo
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Fri Sep 27, 2013 6:39 pm

It's a new ultimate kit , I did around 450 miles before I holed the first piston . As I say , did about 80 with the next one. I'm going to dump this petrol and go back to using one of my old oko carbs , I have been running a 28mm stage 6 pwk pj carb for a long time no probs , I've got no confidence in it now ,,,

Adam_Winstone
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Fri Sep 27, 2013 6:56 pm

Good luck with resolving the issues. I don't like to hear of any of us having problems with our scoots :(

Adam

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jason frost
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Fri Sep 27, 2013 7:42 pm

If you have the rest set up right I would be looking at the head

gp200ts1
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Fri Sep 27, 2013 8:38 pm

check the cylinder head volume, i blew 2 pistons on my imola before checking the head. it was running way to high compression and combined with the numpty who built the engine before me who put the seals in the wrong way round, i thought changing the seals cured the fault but it blew again, thats when i checked the head. replaced it with one from MB and the scoot has been great since

nellyboyo
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Fri Sep 27, 2013 8:52 pm

I haven't checked the head volume, I might have wrongly assumed that fitting the whole new "ultimate kit " and checking the squish ( 1.5mm to be safe ) would be enough .....
Have not told the missus yet ...she`ll kill me

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