Motobecane - slower than it should be

I just got a new motobecane in, and it's acting kinda sluggish. It starts great and has pretty good accelleration - but it's only getting 20-25mph.

I have another 50v I just finished building and it's doing like 35!

So maybe this is a slower model. How can you tell the difference between the models? The only noticable thing I can see is my new one has a bigger rear sprocket (though that should get me faster top-end correct?)

Help pleeease! I want this thing ready to ride this weekend.



Re: Motobecane - slower than it should be

Jason Luther /

larger rear sprocket means slower top end, but acceleration should be faster

Re: Motobecane - slower than it should be

Let me add... I have cleaned the carb spotless and made sure all chains have correct tension

The only thing I haven't done is put a new spark plug in it (The shop had to go get some from their warehouse, and will be there first thing in the morning). The current spark plug looks pretty new though, and is correct.

I have not looked at the clutch or points. It looks like the guy before me put a brand new condenser on it from looking at it. I hope this has nothing to do with points - something I have yet to try. Bleh.

Re: Motobecane - slower than it should be

Ahh, oops. Would that slow it down that much? Do you know how I can tell the difference between the two models? On the tag, in the first box (The one that doesn't have anything next to it) says "4" and then it's 50 "v", and then "A" miles.


Re: Motobecane - slower than it should be

it could have restrictors either in the carb or air box

Re: Motobecane - slower than it should be

My understanding is that Motobecane made 3 models with the 50V: "A", "B", and "C" Models. The "A" is the slowest and "C" fastest. I personally have "C" & "B" Models. Hope this helps.

Re: Motobecane - slower than it should be

Mike Scouty McScoutington /

the intake is smaller i believe. in addition, the carb is also smaller. if you want something to consider, stock mbk spark plug boots are rated as 1 K ohms and ngk makes a boot the is rated to 5 K ohms. this means stronger spark.

Re: Motobecane - slower than it should be


First, congrats. This is the off-road 50V with the big exhaust on one side, right? I meant to bid on that and forgot, but I'm glad someone from MA got it.

I wouldn't bother messing with your spark or anything, it sounds like the bike's working exactly as it was designed to. The large rear sprocket is probably there because this bike is designed to be able to go a little farther off-road than your average moped, and would need the extra torque to surmount steeper hills, ruts, etc. It sounds like switching to a smaller rear sprocket is your best bet for speeding it up.

Re: Motobecane - slower than it should be

where can you get the spark boot your talking about? i have the original and would like to try the 5k?

Re: Motobecane - slower than it should be

You can get that boot here...

Re: Motobecane - slower than it should be

As I have been told, the speed ratings work like this: A = 30(34)mph, B = 25(29)mph and C = 20(24)mph.

My stock "A" model 50V goes better than 30mph.

Re: Motobecane - slower than it should be

Mike Scouty McScoutington /

1977 sells them for $2.99 each and i think they charge $1 a foot for new cable. you can call them at (269)344-1977

Re: Motobecane - slower than it should be

The manifold looks giant compared to my other bike (that goes 35), I dunno if it's bigger on the inside or not. I put the boot from the other motobecane on this one (the one this one came with was pretty shitty looking).

Re: Motobecane - slower than it should be

Actually it's this one,1&item=4558825675&sspagename=STRK%3AMEWN%3AIT

But I won that off-road one last night - can't wait to get it in!

Re: Motobecane - slower than it should be

Argh, which one is it? Is there a way to officially tell via manual that anybody has? I just want to know if I should look for a new carb/intake or not.

I have 3 motobecanes. 1 didn't work, and it was the C model (it has a smaller rear sprocket). I then bought this absolute spraypainted beater that ran (35mph and had a larger rear sprocket) and put the engine on the other bike. Unfortunately the beater-that-went- 35's label was pulled off of it. So I don't know what model it is.

You've got the good one!

A is the fast one.

it has a large rear sprocket because it has a variator clutch. (this is good)

This bike can go faster than any other stock moped.

My 50v "A miles" goes over 35 on flat right now (stock). and it has great acceleration.

If someone replaced the condenser, then they removed the cam. this means the timing has been messed with.

-Is you variator working?

take off the belt cover, and never put it back on. take a ride and watch the belt, does it start to variate.

-Check your compression

-Check your timing

-Check the numbers on the carb (AR.#.#.###)

-before buying a new spark plug boot, take it off, trim the spark plug wire on both sides, and replace

Re: You've got the good one!

Whew! Well that's somewhat good news.

Okay, in frustration I took the carb and manifold off the one that's going 35 and put it on this one. Still no luck!

Carb: AR2.12.873

It variates fine. I've trimmed both end of the spark plug wire - and put the boot from the 35mph one on there.

Good lord, it might be timing huh? Sounds like a bitchass process.

Re: You've got the good one!

Mike Scouty McScoutington /

timing isnt bad if you have the tools.

Re: You've got the good one!

Mike Scouty McScoutington /

dan do you ahve any belt covers? i know of a couple of people here in kzoo that would be interested in one or more if you have any.

Re: You've got the good one!


- Allen wrench

- Wooden ruler broken thin on the centimeter side so it can fit in the spark plug hole.

- Screwdriver to adjust points

- Thin piece of paper

I've got the flywheel off right now. Maybe I should go to Office Depot and get to it.

What else can I use besides an allen wrench? I don't have one laying around.

Re: You've got the good one!

By belt covers are you talking about the little metal piece that fits onto the engine to cover the belt a little? Those are pretty.

Re: You've got the good one!

yeah thats what I am talking about


Yeah I've got a few.

I like to be able to look down to see the state of the variator while riding.

I also like to be able to remove the engine easily.

I am selling 2 50v's right now, so I figured I would give them to the future owners.

I may still have an extra or 2 though.

AR2.12 is the right carb.

setting the points gap is only usefull for a slight timing shift.

a cam puller is need to really change the timing.

you can atleast check it though.

you do not need an allen wrench. Anything you can put on to the piston top and watch go up and down will work.

If you do not have a multimeter, you can use a piece of cigarette paper, or the plastic wrapper off a box of cigarettes.

place it between the points, and pull slightly on it. as you rotate the engine, and watch the ruler you will feel the paper give as the points open. they should open 1.5-2mm before TDC.

if the timing is good, then it is time to check the compression.

you should also check for carbon build up in the muffler and exhaust port

Re: You've got the good one!

Mike Scouty McScoutington /

if you do have a couple of extras drop me an email and what not. im sure that we could work something out with payment or something if you want to unload them.

Re: You've got the good one!

The belt covers give the engine a nice clean look. I'm all about looks I guess.

Okay, I have a clutch puller for it. I'm not quite familiar with the 'cam' but I'm sure I can figure it out. I haven't done much at all with electrical systems yet - though I rebuild analog synths so it shouldn't be too difficult.

I wish I could watch somebody do it once before I rip this puppy apart. Thus is life living in non-moped country. You should create a video to go along with your wonderful little manual.

Re: You've got the good one!

Ok, this thing is truly going to be the death of me.

Timing is perfect

New spark plug

New belt

Tried different carb (same model)

It's still going 20-25.

The last thing is compression I guess. I don't have a guage so I'll have to go buy one.

Is there any last thing to try?

Re: You've got the good one!

Mike Scouty McScoutington /

take your pipe off and see if your exhaust or port are partly clogged with carbon and crap. that can give you a little more. did you buy the right belt, or jsut one from a hardware store? the belts that i have gotten from the hardware store are close, but not exactly right.

Low Compression?

Okay - exhaust port is good and clean. The belt is the correct one.

I went and bought a compression guage - and it looks like it's getting low compression (90) ? One of my Puchs gets 120, and somebody said that was "_okay_".

New rings? Piston? Cylinder? All of the above?

If I need a new Piston or Cylinder - are there any good performance ones to get? I don't want to get a new exhaust.

Re: Low Compression?

I forgot to mention - I looked in the exhaust port, and the piston looks a little banged up which could obviously cause this. Should I just be safe and order a complete cylinder kit from MopedJunkyard ($130)?

Between the ABC models, is the cylinder/piston different? I have a few beaters that I could steal them off of to try out - I just don't want to put a smaller one on there not realizing.



Re: Low Compression?

my best 50v measures at 160# compression

allthough I am not sure I used the tool correctly.

90 is bad

here you go!

Re: Low Compression?

Glad we seemed to have finally nailed this down.

I've got an absolute beater motobecane:

It's a C model - if I take the cylinder/piston off of it, will it fit on my A? I sure hope so - if that doesn't work, I'll order the one on eBay.

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