hello everyone...
i´m from hamburg, germany...and our mopeds are extreme restricted so they run about 25kmh...
and so my n150 (restricted 50) does.
no variator, 10mm bendy intake, gurtner ar 2-10, oval exhaust pipe...
i don´t really know about my cylinder, i´ll tell you tonight...

1.i think my piston was squeezed in the past...it turns freely and it has a normal compression but the piston has some vertical ´´traces´´, at that spot it looks like a cast-iron piston...

my cylinder looks perfect...

2.the intake isn´t fixed with some regular bolts, their head is flat without any slots or anything else you could use to turn them...
i tried to remove one by miling a slot and using a screwdriver, but there was no chance...
í´ve got a dellorto sha 13/13 and could make an intake for it, but first i have to remove the old one.

2.the exhaust port doesn´t open alle the way, at tdc the piston blocks 1-2mm of the port, i´think it´s the same thing with the transfers...
i herard about a similar problem with some 70cc parmakits but mine is definately an original 50cc.


it runs and it accelerates good, but it´s very sensible about the ignition timing.
it often makes some strange sounds, sometimes like a bell??? but only at lower rpms, at higher it sounds good. may this be a consequence of the squeezed piston?

hope you know what to do,
mr. moby

Can you post a picture of the intake bolts?

The vertical traces on the piston - scuffing - can be polished out with fine aluminium oxide (corundum) emery cloth. Check that there is no shadow on the inside of the cylinder walls corresponding to the piston scuffs. The cylinder can be polished out with the same aluminium oxide in a butterfly hone if it is heavy deposit or just chrome polish on cloth in the butterflu hone if it is light marks. The cylinder walls are shrome and should be like a mirror finish.

With the piston at bottom dead center and the ports are partially blocked at the bottom of the port and at top dead center the intake is blocked at the top the cylinder can be shimmed up a little with a thicker base gasket.

The ignition can be retarded slightly to closer to 1.5mm if you have a derestricted exhause. Stock band seems to pull nicely then hit a switch that turns off the pull, retarding the timing wakes up the motor a little bit in the top end of the rpm band.

I am not a huge fan of a lot of the kits for the engines, I have found the quality of the castings is often very poor and high grain alloys which do not machine well.

but using a thick base gasket will cause a poorer compression...should i use a thinner head gasket too?
i´ll make some pictures tonight (well, in about five hours, time shift canada-germany?????)

Yes - placing double thick base gasket will move the port floors higher in relationship to the piston and will raise the cylinder deck higher. To compensate you can place the thinner Motobecane gasket 0.6mm thick. You also could get some copper sheet 0.4mm or 0.3mm thick and cut a new head gasket then heat it with a propane torch and quench it in water or oil to soften the copper so it seals well. The copper gasket can be reused multiple times if you soften it up after each use with heat and quench method. The copper sheet can be bought in a hobby shop that has supplies for card making.

for my cady i made one out of thick aluminium paper, it worked very well...
my fucking camera is broken,´i´ll post some pictures later...
i polished both, piston and cylinder and it worker well...
but my piston looks worse...i thougt i looked better...
in two weeks, i´ll work at a motor-shop for some time...
i hope i´ll be abled to convert a piston from a 103 (i found in my garage) to my moby cylinder...
it´s about 40mm, so i´ll have ca. 55cc if everything works fine

Aluminium paper works well if it does not have a head leak. If you get a leak it will evaporate immediately from the heat scorching.

If you can turn down the piston it will work - if you open up the cylinder you will need to find a place that can do industrial chrome plating to rechrome the cylinder. Opening up the cylinder will be difficult to open through the chrome without damaging the aliminium. Perhaps you should look at eBay or LeSolex for a piston.

i think someone there can do, we´ll see...
so, motor is complete again, better compression i think???
i didn´t use another base gasket, i worked the piston so the gas can flow freely through the intake port and through the exhaust port...i think it will work fine, we´ll see...

some photos...
she´s complete again, runs about 35kmh, feels a bit better now...
downhill, she does about 42kmh, at 45 she starts to sound strange again, like a bell???
finally, some photos (from yesterday...)

That is a very nice looking moped. I can see the intake is very similar in design to the one on the mini-moby. You would need to grind the tamper proof screws, drill two holes, tap the holes and have two studs added if you want to change manifolds. That is annoying to do but then you could swap to a more common manifold which would allow some flexibility in chosing carbs.
The bell sound could be running too lean or if it seems to be on the left side only of the engine it could be the dimoby clutch over running.

no, it´s from the cylinder...
i had to cover the holes in my airbox completely to get her running better, so i started ro think about my main jet...i took a look at it, it´s an 48 (seems to bee a late one...)
i had some 210 and 215 left from some cady carburateurs, i tried the 215 (without covered AIRBOX)
semms to run nice, i couldn´t test really, i´ll try tonight...
another picture:

so, main jet 210 is best...runs 45kmh when warm, but sounds really strange
i think i´ll have to buy a new cylinder...
ignition is perfect now.

i tried to remove the clutch (with the puller), i had no chance...instead of removing the clutch, i crashed my brass nut (i forgot to remove)

what do you think about this exhaust?
http://cgi.ebay.de/Motobecane-Mobyx-Bj- ... 3|294%3A50

i´ll have to paint it in black (re-chroming is too expensive), but i like them...
i think it´s the old version:)

The picture from eBay is of a earlier exhause which is a better design. The silencer portion of the exhause is a ball that can be opened a little on the input side to give a better response.