1977 Motobecane 50V Upgrade

Hello everyone,

Just got my Motobecane and would like to start some performance upgrades.

At this point I have done the simple upgrades to see what kind of power I can get out of it for the cheap. Here is what I am currently running:

1977 Motobecane 50V - stock AV7 motor

Airsal 74cc kit

Dellorto SHA 15.15 carb

Stock exhaust

With a GPS I have been able to only get 30 - 33 MPH. My goal is to reach at least 40 MPH comfortably with a nice even power band.

I have looked into the AV10 crate motor (http://www.1977mopeds.com/parts/engine/complete-engines/motobecane-av10-crate-motor.html) but have read the mixed reviews on here. Apparently one can just check all of the surfaces and apply loctite to the necessary hardware and it can run just fine.

Otherwise the Doppler ER3 Variator caught my eye.

Any thoughts on options for my build to help with my goal?

Re: 1977 Motobecane 50V Upgrade

The AV7 is perfectly capable of your speed goal. You'll likely want to stick with it seeing as it already kitted. I'd steer clear of the crate motor. Derestricting the stock exhaust pipe should do you some good. Did you rejet the carb properly?

Welcome to the forum. Couple pages you may want to check out Wiki: Performance Tuning and

RebelMoby's page .

Also, while the ER3 is a nice variator option, the "clutched" model will require a different method of starting the bike(pullstart, kickstart, or cardboard trick). The "clutch-less" model will require the use of a clutch pulley to work.

Re: 1977 Motobecane 50V Upgrade

I'm hitting that on a (ported?) 50cc. sha 1515 with a shorty intake and mesh air filter. topped out at 48 flat gpsed. unrestrict your stock pipe. it helps a lot I've heard. hack out the long pipe in your stock pipe to open up the chamber. also I recommend getting a launch lever. I made my own but you can get one for like $15 on treats

Re: 1977 Motobecane 50V Upgrade

Alex Frank Wrote:

-------------------------------------------------------

> I'm hitting that on a (ported?) 50cc. sha 1515

> with a shorty intake and mesh air filter. topped

> out at 48 flat gpsed. unrestrict your stock pipe.

> it helps a lot I've heard. hack out the long pipe

> in your stock pipe to open up the chamber. also I

> recommend getting a launch lever. I made my own

> but you can get one for like $15 on treats

How many mesh layers do you have in that filter? I have close to the same setup as you and I top out at about 30 flat.

Re: 1977 Motobecane 50V Upgrade

All you'll really need to do is change your gearing. a 48 tooth rear sprocket will put you just where you wanna be.

Re: 1977 Motobecane 50V Upgrade

Thanks everyone. I am going to try to work with what I have at this point. Unrestricting the exhaust will be my next step. Any experience with power contrast between an unrestricted blunderbuss and an aftermarket pipe with a larger expansion chamber? Some research shows: "Expansion chambers almost always have turns and curves built into them to accommodate their fit within the engine bay. Gases and waves do not behave in the same way when encountering turns. Waves travel by reflecting and spherical radiation. Turns causes a loss in the sharpness of the wave forms and therefore must be kept to a minimum to avoid unpredictable losses." This brings me to believe that the aftermarket models might offer an improvement over the stock blunderbuss.

I have upjetted the carb but not sure if I am at the optimal setting yet. I have a few to play with yet. Need to just play with them and check the sparkplug to see where I am at.

Also, will check to make sure that my tires are properly inflated as well.

Any thoughts on if my timing should be adjusted since I have a larger kit? If so, has anyone had beneficial results with adjusting the contact breaker point gap or the actual ignition timing?

My manual states the setting to be: Timing Spec: 2mm BTDC ; Point Gap: 0.35 - 0.40mm

Re: 1977 Motobecane 50V Upgrade

Downhill Harvey (OFMC) /

I'd start with a temp gauge. It will tell you how much every modification affects the engine.

Re: 1977 Motobecane 50V Upgrade

If you buy a Doppler pipe for that thing and use the header spacer, a few things will happen:

1: You'll overheat that poor little engine in short order.

2: You'll more than likely snap your crank or cause other hideous damage.

3: You'll have to lose your pedals, kickstand, or both

4: You'll have to use much lighter variator weights and/or get a much stiffer engine return spring/Launch Lever

5: You'll want to regear thoroughly because otherwise you'll be doing 45MPH at 9000 RPMs, if you can rev that high.

Re: 1977 Motobecane 50V Upgrade

max g Wrote:

-------------------------------------------------------

> Alex Frank Wrote:

> --------------------------------------------------

> -----

> > I'm hitting that on a (ported?) 50cc. sha 1515

> > with a shorty intake and mesh air filter.

> topped

> > out at 48 flat gpsed. unrestrict your stock

> pipe.

> > it helps a lot I've heard. hack out the long

> pipe

> > in your stock pipe to open up the chamber. also

> I

> > recommend getting a launch lever. I made my own

> > but you can get one for like $15 on treats

>

>

> How many mesh layers do you have in that filter? I

> have close to the same setup as you and I top out

> at about 30 flat.

hit more than 50 down hill with no filter, but I'm running a treats 60mm high flow screen filter now.

Re: 1977 Motobecane 50V Upgrade

Alex Frank Wrote:

-------------------------------------------------------

> I'm hitting that on a (ported?) 50cc. sha 1515

> with a shorty intake and mesh air filter. topped

> out at 48 flat gpsed. unrestrict your stock pipe.

> it helps a lot I've heard. hack out the long pipe

> in your stock pipe to open up the chamber. also I

> recommend getting a launch lever. I made my own

> but you can get one for like $15 on treats

How did you port the stock cylinder.

Which pipe do you have and how far did you hack off the tube.

?

Re: 1977 Motobecane 50V Upgrade

I honestly have no clue if it's ported. When I bought it it was 4 stroking so I got a better filter than the stock sha and the pipe is the stock cashew with no inner pipe. just went on a cruise yesterday with my friend, he has an 800cc cruiser. I was capable of cruising and keeping up with him haha... until we hit hills.

Re: 1977 Motobecane 50V Upgrade

This is the pipe. only changes I made were that I painted it black and chopped the inner pipe making one big chamber.

http://www.treatland.tv/MBK-AV88-stock-chrome-exhaust-pipe-p/mbk-av88-stock-pipe-chrome.htm

Re: 1977 Motobecane 50V Upgrade

Alex Frank Wrote:

-------------------------------------------------------

> I honestly have no clue if it's ported. When I

> bought it it was 4 stroking so I got a better

> filter than the stock sha and the pipe is the

> stock cashew with no inner pipe. just went on a

> cruise yesterday with my friend, he has an 800cc

> cruiser. I was capable of cruising and keeping up

> with him haha... until we hit hills.

so chop the whole tube all the way down to the sheet of metal that devides the chamber ?

Re: 1977 Motobecane 50V Upgrade

I chopped it off so it's flush with the end cap lip. like the pipe is only an tiny tube at the very tip

Re: 1977 Motobecane 50V Upgrade

would i cut where the red line is? (edited)

motobexhaust.jpg

Re: 1977 Motobecane 50V Upgrade

Capture.PNG

that's where mines chopped. as close to the end as possible

Re: 1977 Motobecane 50V Upgrade

Raymond Magsaysay /

Hi I noticed your very knowledgeable. I just got a mobylette with an Av7 motor. A friend of mine recommends getting an av10 motor. Just wondering if you have any advice as to how I can improve performance on the Av7 and if it's worth doing do so or just get the av10 and upgrade it?

Thanks

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