Motobecane 50v starts but that's about it. what now?

Alden Stover /

Oh this bastard moby. I've been learning/working on this for quite a while. It now starts but isn't ride-able. Currently it won't run at idle and when giving it gas it seems unstable; being super weak one moment and then suddenly some pep comes out of nowhere. Also the damn drive pulley clutch doesn't seem to want to catch most of the time, so no power to the wheels and the engine isn't swinging back (the first time I started it, the variator seemed to be working fine and now it won't). I'm not really sure where to go from here. I'm really hoping not to blow it up. Check out the video of it here (the throttle is nearly all the way open, and you can hear it change power at one point):

Things about the bike:

-New bearings, seals, and gaskets (afterwards did a leak test with engine starter, with no changes in idle)

-New coil and condenser

-New motor mounts

-I have some dellerto clone on it (I don't know the size) with a 71 jet (larger jets seemed to bog it down more)

-airsal 74cc with extra thick base gasket, original head.

-variator has been lubed. all of the clutch pads and internal arms seem good. there does seem to be a little too much play on the crank shaft. I can shift the variator 1-2mm back and forth

-recently the brake light went out (could that somehow be affecting my performance?)

Re: Motobecane 50v starts but that's about it. what now?

pedal switch in engine mode? starter clutches not sticking?

Re: Motobecane 50v starts but that's about it. what now?

Moped Lar (OFMC) /

Why do all that work and then put a cheap ass clone carb on it? Spend the few extra bucks and get a genuine Dell’orto for it. I’ve bought bikes with clone carbs and they all ran like crap until I swapped them out for the real deal. I’m not saying that’s 100% your problem, but that’s where I’d start.

Re: Motobecane 50v starts but that's about it. what now?

triple check your timing, points. i dont think moby ignition goes thru brakelight but is somehow attached to that horn button/ kill switch/on off. your clutches should definitely catch at that speed. once timmed, spray some premix directly into carb to find out if its lean. the exhaust nut is loose but check if the muffler clogged?

Re: Motobecane 50v starts but that's about it. what now?

Alden Stover /

I definitely have the pedal switch to engine mode. I'm not having an issue with the pedals engaging the motor. It's that the clutch isn't translating power from the motor to the wheels. I'm assuming its the interior pulley drive clutch, but the arms, springs, and pads look just fine.

I'm sure that the timing could be adjusted. It seems to slip on me regularly, so I'm always resetting it.

The muffler isn't clogged.

The carb is a runtong and while a clone, I can't imagine that's the source of performance issues. It doesn't leak, seems to deliver gas and air properly.

Currently my priority is getting the clutch to engage correctly. It's going to be difficult to work on performance if none of the power is getting to the wheel. It seems that there's plenty of talk on mopedarmy about dealing with the starter clutch but damn near nothing about the pulley drive clutch.

Re: Motobecane 50v starts but that's about it. what now?

the arms inside are starter clutches, swing out when u pedal.

the three leafs along the outside are your go go clutches, r they there?

Re: Motobecane 50v starts but that's about it. what now?

Alden Stover /

oh damn, have I confused which part of the clutches do which? Well, the outer leaves are there and don't seem too worn...

Re: Motobecane 50v starts but that's about it. what now?

Just my opinion, but stop wasting start spray shyte, that 'trick' is rarely effective, but keep at it if you want to kill extra time. Give the engine a proper leak down test to detect vacuum leaks.

If I had that bike I would give is a going through and check a number of issues that you might have overlooked during overhaul and modification.

Carb - SHA15:15 did you put a oring between the carb and 15mm intake. 11/16 X 13/16 X 1/16 oring will suit the 15mm SHA. Make sure you derestrict the intake if it necks down from 15mm where it transitions from round to rectangle. You would need jet in the 74-78 range when you decide to put a goodly pipe on that instead of the stock pipe.

Exhause - is it stock exhause completely and no derestricted? The higher volume of air-fuel being processed bu the bike needs to breathe, derestrict the pipe or get a good aftermarket one on there. Stock exit should be opened to about 11mm ID (not bigger) for the kit and carb. Use a new crush gasket and tight her right tight, first time you get the engine heat soaked check it is still right tight while the engine is still cooking hot.

Timing - for stock points set the points to 0,40mm (.016 inch) at index, timing should be 1,5mm BTDC. Plugs should be gap at 0,40mm.

Kit install - did you index the kit to the motor or just throw on a thicker base gasket? Index the kit by putting the piston at BDC and check that the edge of the piston aligns with the floor of the exhause, Use gasket material of proper thickness to make that alignment happen. For the ring gap, if you have no kit manufacture spec it is 0,004 per 1,00 of bore, you need that to be correct, it is only coincidental if it is correct with a new assembly, they are not pre-gapped from the manufacturer.

Clutch is not hooking up in that video. On the clutch, the inner arms are for starting and the pads on the periphery of the cover are the main clutch. First make sure the starter arms extend fully to the outer bell without effort with their little springs unhooked. Even if its starting action seems to be acceptable. Make sure the friction surfaces inside the cover and inside the carrier are free of surface rust, you can scrub them goodly with 220 aluminium oxide cloth. If the main pads are not squared then they may be worn too much, so if the tips of the friction material is worn down you would want to change them out, or change the entire cover. Treats sells the main clutch pads, there are two sizes of rivets used in Moby main clutches, 3mm and 4mm. Dont know what size this set comes with but you will need those drill bits to drill out the original pad's rivets anyway.

https://www.treatland.tv/motobecane-stock-clutch-PAD-n-RIVET-set-p/mbk-clutch-pads-n-rivets.htm Treats also sells the cover as an assembly https://www.treatland.tv/motobecane-stock-clutch-drum-p/mbk-clutch-drum.htm but you need to wire weld the cover to the core before using it because they are not very well assembled from the factory.

Hope some of that helps.

Re: Motobecane 50v starts but that's about it. what now?

Alden Stover /

Ok update:

Yesterday I went into the clutch, cleaned out the bell and scuffed up the pads. After cleaning the carb adjusting the timing I got it running and the clutch catching. Though it still doesn't want to idle, with a little throttle it stays running. I immediately switched to a 79 jet, out of concern that if I have it too lean it'd lock up.

Admittedly this time around I advanced the timing further than usual. I've had quite the issue with the timing slipping which puts it too far behind. My hope is that it'd slip to where it needs to be. I should probably get the proper tools for this as I have been setting the timing by feel and according to the markings on the cam. I've also entertained the idea of lapping the crankshaft so the cam can hold better.

So I took it for a bit of a ride, and currently it's fairly slow and the engine seems to be vibrating too hard, but it's running. I took a mile long cruise to a restaurant I work at (though shut down due to corona), and there I borrowed an infrared thermometer. The motor registered just above 200 degrees, which is surprisingly low. After riding back home, I gave the motor a good look over. I see no leaks coming from any of the gaskets or anything.

It's my current assumption that I'm running too rich and need to work my way down on jets. It also appears that my throttle is set so that the carb can't open up all the way, which I'll adjust.

I have a stock pipe but I do intend on derestricting (though note, I'm not trying to have a screamer; I just want a bike that can handle hills)

I have the engine properly indexed, which took a 2mm handcut base gasket.

I'll have to check but I'm fairly certain that my carb doesn't have an o ring, and I'll have to look into derestricting the intake.

Hearing about ring gap is new to me (I'm learning on this bike and just had to google that) but should I assume it's coincidentally correct since it hasn't snagged in the cylinder?

Re: Motobecane 50v starts but that's about it. what now?

> Alden Stover Wrote:

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

> Hearing about ring gap is new to me (I'm learning on this bike and just

> had to google that) but should I assume it's coincidentally correct

> since it hasn't snagged in the cylinder?

Assume nothing . The only way to know for sure is to physically check it .

Re: Motobecane 50v starts but that's about it. what now?

If you have been "setting the timing by feel and according to the markings on the cam" you need to be a bit more accurate. The "divot on the cam" trick is just an indication of where it should be, unless you are at the Pantin factory over 40 years ago on the assembly line there is no accurate way to use that mark. BUT there are no fancy tools needed aside from the puller and a piston stop tool.

Check the timing

Adjust the timing

Make a piston stop

Re: Motobecane 50v starts but that's about it. what now?

^ So cool this information is immortalized on the internet.

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