Vespa et4 125 slow ? please help!!!!!

When fitting a new top end you may have broken the piston rings. On a Two Stroke engine the rings have a gap which must not enter any ports. To prevent this the slot for the rings has a metal peg to hold the ring gap in one place.
On Four Stroke engines there is no ring peg as there are no ports.
If a ring breaks whilst being fitted the broken parts will enter a port and then be dragged up and down the barrel causing damage to piston and barrel. The broken parts one having made their way to the top of the piston will be crushed between the cylinder head and the piston damaging both. The cyl head can be re used but the piston is most likely ruined.

Pete

- this problem might be a worn variator belt/rollers - Vespa technology requires a variator-belt service every 10'000miles
- contrary to the belief that the carburetor causes such trouble...

Yes it can be bored, .050 over is fairly common on this bike. Before boring the cylinders, the new pistons should always be matched to the old ones. You always find problems with aftermarket parts. Have the cylinders bored to match the new pistons. Don't bore the cylinders and expect the new pistons to be a perfect match. I hope this helps.

G'day. The torque specs for the 8mm head bolts is 18ft/lbs.the jug?(cylinder or barrell) is just tightened down even & firm, as there is no acess for a torque wrench.
OK. other things to note.
Clean the cylinder first in solvent(kero or fuel).Then in warm soapy water in a bucket. Dry-(compressed air is best for this-wear eye protection).once dry lubricate all power valves with oil.
Using a clean white rag-soak the end in your 2 stroke oil & wipe the inside of the cylinder surface untill the rag comes back clean(you will need to do it a couple of times-turn the rag over & do it again).Lube the new piston just before assembly-Also pour a little oil down the main bearing oil holes & over the big end too.
Other things to be sure of are-
Piston on the right way round-arrow to the exhaust.
Rings right way up. Some 2stroke dirtbike rings will only go one way up.Look CLOSELY at the ring ends-on the upper or lower surface there may be an etched dot or "T" or "N" or other marking. the mark goes facing up(on both rings unless single ring piston).
rings positioned with end gaps over the locating pins(the ring grooves have a pin in them to stop the ring turning)
Piston pin clips in correctly.
Powervalve moves freely.
Again-watch when you fit the cylinder-it can be tricky to keep the ring end gaps over the locating pins as you feed the cylinder over the piston.
Hope this all helps
Regards(done this a thousand times)Andrew Porrelli

Poor compression I expect. Fit new rings and rebore the barrell to bring the compression up again. Using easy start or eather will damage the piston and seats.

It seems you have worn rings and/or barrel and piston. You will have to get the barrel off the engine to ispect. Unbolt the carb and exhaust from the engine. Unbolt the 4 nuts on top of the head. Remove the head and barrel from the engine. Inspect the piston for scoring and wear. Remove the piston by removing the circlip next to the gudgeon pin. Do not drop the clip into the engine.(stuff some clean rags in the engine under the piston. The gudgeon pin can now be pushed out of the piston and the piston removed.Have the barrel and piston measured for wear.
If you're on a tight budget you can replace rings only but this is a penny wise pound foolish solution. You'll have the same problem in 2 months time.
It is best to rebore the barrel and fit an oversize piston and new rings. The barrel can also be resleeved but this is a more costly option and should only be exersized if you cannot obtain an oversize piston.

when your putting the barrel back onto the piston start lowering it down. when you lower so far swing the power rod into posistion cause you cant fit it after you have reinstalled the barrel. hope this helps just fitted a new piston and rings on ma kx80 and a had the same problem lol

Hi
Sounds like a broken piston ring, & now its embedded itself into the piston & / or barrel
Remove exhaust pipe & shine a light up into barrel / piston to inspect !!

Ride safe
Bike-Doc
Please mark this as very helpful (if it has been!!) - it helps my ratings

I am pritty sure were talking two stroke here. i would suggest that you have made a mistake on re-assembling the top end.
First remove the head only.
Now try to turn over again.
If it turns over now your head gasket is at fault.
If it is still seized/won't turn over you may have installed the piston backwards(should be arrow to exhaust) or have installed the rings without lining up the end gaps with the locator pins that are in the ring groves.
Check these. If you're sure this is right, remove barrell/piston/rings.
Now check the fit of the piston in the cylinder. Make sure it moves freely & dosn't bind. Now insert the rings (one at a time) into the barrell & check the end gaps.

Hope this helps narrow down the problem.
Regards Andrew Porrelli