MOPED ARMY

get the 15:15, with the cable choke. it fits the bendy intake just fine. i just bought one from '77 and it was shipped super quick. you may also want to get one of those high flow air filters they have too. it comes with a 68 jet but you'll want to jet it somewhere between 56-60 stock depending on whether or not you get that filter and stuff.

as far as porting, you'll want to raise the exhaust a little too. its not going to hurt anything and it will be necessary to gain the most power from the motor. the porting instructions in the wiki suggest 3mm, so go with that. changing the intake port as specified by the article in the wiki will increase the intake duration (or the time that the intake port is open) and that is a good thing, and will allow you to make the most of the larger carb and what not.

gearing: its not really a good thing to ditch the stock gearing with a variator. using a larger sprocket up front, or smaller one in back keeps the motor out of its powerband too much of the time and kills low end and makes the bike take forever to reach top speed. go 11/54. low 40s is definitely attainable, even with the stock exhaust.

"here":http://www.mopedarmy.com/wiki/Motobecane_porting is the wiki entry I made on porting.

The bits I like to use are the tungsten carbide cutting bits. They're a little pricey, but they won't load up with aluminum like wari says. They also come in a lot of sizes and the smaller ones allow me to get into the transfer passages to open them up.

I do my cleanup with the little sandpaper bits that come with every dremel kit.

I'm sure everybody has their own methods, but these two work the best for me.

And by "working the transfers do you mean widening, polishing, or ?

and ALWAYS put a little radius on the edges of the port, even if you are not doing any port mods it is worthwhile to extend the life of the rings and ensure sealing. you neva want a sharp edge on the port, the sharp edges are there stock because of manufacturing costs. also put a radius on the bottom of the piston skirt while you have the cylinder off.

dip your carbide bits in grease first and use slow speed the grease will hold most of the little metal chips. you have to flush all the cylinder LOTS after machining to make sure there are zero metal chips that are left behind on the cylinder cause that can give you a very bad day.

port that bitch yo

This is kind of a bump, what can I expect with an all stock bike except the addition of a Ninja G3 performance exhaust and 15.15 Dellorto? Speedwise of course. Is the 15.15 the best one to get for that setup, would it fit on stock short intake for fast moby, and do I have to mess with timing at all? (one of my fears).

I've heard that the ninja doesn't give much of a performance boost without a kit. It does sound awesome though.

Steve, when I say "work the transfers," I mean widening and polishing. Make them bigger!... but not too big!

haha.

Nope, and I only use that as a rough guide. I found those pictures from something Bret posted and used them to make a general porting entry.

If you're going to not mess with the timing, you should mostly widen the port windows. Don't go up or down with the transfers at all. You can go up with the exhaust and down with the intake without effecting timing. Working the ramps is a big thing, too. Make the transfer ramps huge. There's like 6mm to play with in there and last night Rafter said that he's not done until he can fit his thumb in there (that might be extreme). Then match that to the case.

Good point. Advancing your timing to 1.5 is nice. They say that anywhere between 1.5 and 2 is acceptable, but advanced is much more fun.

dremil tools are fun to play with

Jesse, 1.5 to 2 Mm BTDC would be ADVANCED timing - the spark is going just BEFORE the piston gets to TDC. If you RETARD the timing it is happening after TDC and you're wasting the power of the explosion, hence bikes with retarded timing running really weak.

Advancing timing gives more power, until you get to the point where it is TOO early and you start blowing up the piston.

"Rotary tools are fun to play with"

I like to do port edges with a hand file. There's a jewelers file set at my shop.

I think i'm right that 1.5 btdc is more advanced and 2.0btdc is more retarded. I've been running it over in my head to make certain...?

hmm...don't you do timing by degrees not mm? How do you know that your plug is firing 2 mm before top dead center?

Put something in the spark plug hole and measure back 2mm. Since you remove the flywheel from motobecanes when you access the timing cam, it's easier by this method.

I like to turn a spark plug upside-down and measure using the letters in NGK B6HS. I've found that the letters are about 2.5 to 3mm tall, so i measure from 3/4 to 1/2way down the B, using a cylinder fin as a sight guide.

Wow. I am dumb.

I've been using a very nice timing tool and using factory specs anyways.

Thanks for the clarification.