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Hi got a mugello 198 with reed valve ,had the kit on scoot for about 18 months .Last September the small end bearing failed causing scoring to the barrel and ruining the piston and rings.
I sent the barrel for a re plate and reassembled it with a new piston ,rings and head earlier this year .Every thing else exhaust, carb and ignition remained the same
The scooter started and ran ok in1st ,2nd and into 3rd but after 3/4 throttle the motor began to loose power and not rev on. stripped top end down again to find a piston circlip had made a break for freedom (my own fault ) scoring the barrel again about 5mm above and 10mm below transfer port
My question is firstly would a scored barrel affect the performance that drastically as I have read on various forums of people with scoring from the top to the bottom of their cylinder with no issue,or could the cylinder somehow been wrongly re plated in relation to the ports
I have also tried a mates spare carb ,stator ,cdi and replaced the fuel tap just to rule out any issues there

Hi Simon,

Welcome to the forum.

The symptoms you describe sound like classic over-gearing issue, but as you say, the scooter worked before you had the small end bearing let-go.

It sounds like you are asking whether the engine would demonstrate this same poor 4th gear performance if you rebuilt it with the damaged cylinder. It doesn’t sound like the damage to the replayed cylinder is too bad, so I could only suggest that your best way to evaluate the damage is to rebuild it and give it a try. You may find that the 4th gear issue was just a result of an escaping gudgeon pin circlip.

Sometimes, the only way to answer your question is to try it. Soz.

(Let’s see what others have to say)

Have you measured piston/bore clearance ? Did you send them the piston for the re-plate ?

Thanks for the welcome knowledge, with regards to my post ,I should have mentioned that I have already refitted the cylinder and the poor running still persists As for gearing I have had an li 150 box 15/46 in it for a number of years ,which was a lot better than the original tv 175 box

Hi Mick ,yes sent new piston with the cylinder .If my memory serves me right the bore clearance was about 0.055mm and the piston ring gap around 0.35mm