aprilia rs 125 blown pistons??????

[gedi1305]

hello
i own a aprilia rs 125 2007, i have had the bike since 2012 and in that time i am on my 3rd piston.
the bike is kitted with:
arrow exhaust (140 main jet)
28mm standard carb
derestricted spark plug
standard wood ruff key
ecu has not been tampered with

the first time it went the spark plug had completely detonated and it made a crater in the top of the piston, i bought a new cylinder and piston etc and had it re built. just after i did 600miles another piston went and did similar but the piston had a hole in the top and the spark plug was grey.
after that i had to have the engine fully rebuilt,(piston, main bearings, oil seals, new gaskets etc)
i have just got the built back up and i am reluctant to ride it until i know what the problem is.
soo please if anyone has had a similar problem or knows what it could be, please help?
thanks

[kerr]

Iv no idea about jetting or anything, but i take it your taking it easy the first 700-1000 (i think it is) keeping the revs below 7k if your hammering it right away that could be the cause.
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aprilia 125 Af1 Futura >> Suzuki gsxr 600 srad >> J1 zx6r >> cbr 600rr >> Speed Triple

[Ariel Badger]

For some reason it is running weak, strip the carb, make sure the tank is venting properly.
BTW, what is a derestricted spark plug?
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[gedi1305]

Hello thanks for the reply
How would i check venting
Its just when you der restrict a bike you have to change the spark plug to allow more rpm

[Timmeh]

Methinks your plug heat range is wrong.

What is it?
____________________
GSXR400 x2 | '94 RVF400 | '93 TZR125 4DL (again)
20:22:30 BLUEX5: i would love to be forced to undergo a**l plugging with different sizes
20:48:18 Temeluchus: comp you hunk of smouldering homos3x you

[gedi1305]

The first time it blew the piston it had a BR8EG (i think) and when i looked on PJME website it had a BR10EG and in the description it said "for all unrestricted engine"

[Timmeh]

What make of piston did you use?

Did you bother checking the compression or the squish band?
____________________
GSXR400 x2 | '94 RVF400 | '93 TZR125 4DL (again)
20:22:30 BLUEX5: i would love to be forced to undergo a**l plugging with different sizes
20:48:18 Temeluchus: comp you hunk of smouldering homos3x you

[gedi1305]

It was a miaka piston
And we usded the thickest gasket and i check for compression once it was all together
Just took the spark plug out and put my finger over the hole and pressed the starter and there was compression

[webhead]

I would say its your ecu its restricted I expect give me the number and ill tell you,also put a br8 in it as that would be correct for standard restricted bike, you can cut jumper on ecu to make it full power if you want easy to do, also your jets are way to high for a restricted rs125 ,120 is standard ,mixture about 2 turns and a bit out.

if deristricted put a 132 in , if restricted with air filter mod 128,

also if you have rave unit ,you got to make sure that ecu is deristricted aswell, or you bugger it up again.

and remember you must run it in properly or your blow it like I did on my first rs125 took it for mot it passed and on way back I thought id be celver opened her up for about 1 minute and pop goes my piston lol

and I knew that would happen but I still did it what an idiot lol but who cares.

[gedi1305]

Thanks mate
Was this a similar problem to your bike and Have you sorted the problem on your bike?
Are you after the number on the ECU?
Thanks

[_Iain_]

[Timmeh]

[gedi1305]

The bike is de restricted as far as the ecu, im not too sure if thats de restricted.
Ill try upload a pic for you

[gedi1305]

It wont let me upload a pic
But the number is
0624911002265

[Kickstart]

Hi

Which shape of RS125 is it? Which carb is it as standard?

If it is the rounded shape (could be one of the last ones at that age) with the PHBH 28 carb then the main jet sounds too big. Suggests that if it is burning a hole in the piston that either the compression is too high or the timing too advanced (or you are using pathetic petrol). For the timing check that the woodruff key locating the flywheel hasn't sheered off. Also on these the cdi unit mod does nothing outside the range of 4750 to 6000rpm (at those revs it causes a massive amount of ignition retard, causing a flat spot as standard), so unlikely any change there will cause a major issue.

If it is the newer shape one then afraid no idea on the jetting.

[gedi1305]

Hi
Its the new shape bike and it is a standard 28mm carb
I checked the wood ruff key and thats still fine

[Kickstart]

Hi

If a late shape with the VHST carb then a 140 main jet seems way too small. These run very different jetting to the older phbh carbed bikes.

Think the Aprilia guide for de restricting them lists changing the main jet from a standard 132 up to a 185.

All the best

Keith
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[bladerunner]

A hole in the middle of the crown is caused by lean mixture or to hot a grade plug....which you ain't with a 10. And std Cdi should be fine if std woodruff key used. Either air leak or lean jetting. Jet up a couple of sizes and do a plug chop.
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

[Blau Zedong]

Why do you keep throwing pistons at a bike with a setup issue? Seriously there is zero point fixing it until you know why it's melting pistons. Although am betting it needs jetting properly.
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[gedi1305]

Hi
Thanks for the advice
So what size jet would you reccomend?
Parts fitted:
Arrow exhaust system
Pipercross panel airfilter
Standard 28mm carb

[webhead]

hi dude I cant tell with that ecu number so its haven't a clue on it , I would buy 1 that says its derisricted and try that, if I was you I would use a 128 main jet, go down road and check color , keep checking it until right , or your just going to keep blowing them pistons up, rs125 are very fragile but great when there right.

[Timmeh]