Motobecane runs like a champ! but only when choked

this is related to the recent posting about recommended mixture ratio.... We just got the '78 motobecane 50v started up today and she runs very smoothly. Everything is stock, besides to the new gaskets, very clean, almost like brand new. The problem is this: with 50:1 fuel (synthetic oil) it tops out at about 24 and has sluggish acceleration. When I engage the choke about 1/3 of the way and hold it the moped runs perfectly with great acceleration and 30 mph top speed on the flats. The manufacturer recommends a 32:1 mixture but since I used very good synthetic oil I thought 50:1 certainly wouldn't cause any lubrication problems, but is this causing the fuel mix to be too lean? What would you suggest I do in order for the ped to run well without having to hold the choke? Thanks.

Re: Motobecane runs like a champ! but only when ch

See Ya Moped Army /

Check the fuel flow from the tank to the carb. Also make sure the main jet is clean. It sounds like it's starving for fuel.

Re: Motobecane runs like a champ! but only when ch

this moped is 100% clean, perfect fuel flow, spark, compression.... everything. This moped has been totally disassembled, cleaned, and reassembled. I guess my question is does a fuel mixture with less oil make the combustion leaner than a fuel mixture with more oil (i.e. 50:1 vs. 32:1)?

Re: Motobecane runs like a champ! but only when ch

Also, the moped continues this behavior even after thoroughly warmed up.

Re: Motobecane runs like a champ! but only when ch

See Ya Moped Army /

What makes it run lean/rich is the ratio of fuel to air. Running a 50:1 gas/oil mixture should not cause the problem you are experiencing. The only other thing that could cause this problem is the float level. The fuel may be cutting off too soon because the float is not adjusted properly.

Re: Motobecane runs like a champ! but only when ch

im having same pro with my ttlx to

Re: Motobecane runs like a champ! but only when ch

Can you tell me how I might go about adjusting the float level? It is a gurtner carb with a cylindrical looking float and a needle that comes out of the top, I don't see how this can be adjusted. I will try cleaning out the main jet again since it won't hurt to double check.

Re: Motobecane runs like a champ! but only when ch

See Ya Moped Army /

You can actually push the metal needle up or down. If you want to push the float closer to the non-pointed end of the needle, just apply pressure to the float and push down on it. The float should slide pretty easily. If you need to move the float in the opposite direction, it's a bit trickier since you don't want to bend or distort the pointed end of the needle. Use something firm, but flexible, so you don't bend the needle when applying downward pressure. Someone may have a better method of doing this, but this works just fine for me. Also, make sure the pointed side of the needle points upward when replacing it in the bowl.

Re: Motobecane runs like a champ! but only when ch

Is ther a ruber gasket around your like float bowl at the top and like a black bar with two little hole groves that go onto the cover is that the carb ur talking about and the float has a needle going right throught it?? I had this problem because my ruber gasket wasnt working probrely it was sitting funny if it isnt sealed it spills some gas out alnog with not enuf suchion so the fuel doesnt get in fast enuf mighn would run for like a couple of feet and then i would have to hold the choke to keep it running it seems to me like u have a lesser case of what happend its defanatly get soething to do with the about of gass gettign in changing your oil ration has no affect of short term running quality i ran mighn on pure gasoline all the way home about a mile and it is fine the leaner ur fuel oil ration lean being less oil rich being more the leaner it is the more top end u will have altho if ur running no oil slight damage that will occur over a long period of timewill happen check all ur seals encluding ur head gasked .....Make sure the two surfaces it is touching are not bumpy at all if they are this will cause not enuf compresion and DO NOT PUT ANY STREESS ON YOUR ENGINE untill you have checked to make sure they are perfectly flat or u will blow ur head gasket. if it isnt flat let me know and i will tell u how to fix it properly i had a comlpletly warped engine the cycender shaft war an ovel and the top or the head was like the rocky mountains because my dad took a hammer to it to try and get a piston in lol i got it into perfect working condition

Re: Motobecane runs like a champ! but only when ch

k? let me know

Re: Motobecane runs like a champ! but only when ch

Is there any holes on your air box if all elts fails plug up one of the holes with some tape that would make it be eqwivilant to holding the choke just a thought

Re: Motobecane runs like a champ! but only when ch

Do you have the airbox on?

Re: Motobecane runs like a champ! but only when ch

It really sounds like a air fuel mix issue.

the choke on a moby is not really a choke.

It is a fuel enrichener (more fuel)

So your bike is running better when you are forcing more fuel into it.

I would flush the jet again.

maybe set the float a bit higher.

If you do not have the airbox on, put it on. that will cut air intake a little and enrichen the mix.

Re: Motobecane runs like a champ! but only when ch

Thanks! I did not know that the float was adjustable, I will do that today. moving the float closer to the pointed end of the needle will make it richer? The airbox and filter screen are in place and clean. Thanks for all the suggestions.

Re: Motobecane runs like a champ! but only when choked

I know this is an old thread, but I had the same issue today on the 50L I am restoring, and I wanted to add my two cents in case somebody else stumble on this thread with the same issue. I have done all that was suggested in this thread, to no avail. I have good fuel flow, good lines, and a shiny gurtner I had super thoroughly cleaned. I did find a tiny crack on the airbox, near the screw, that I sealed, but it did not help.

Looking deeper on the (french) web, I found out a way to access the atomizer (it did not appear to me that I could reach that when I cleaned the gurtner, so I had not cleaned it). The atomizer has two tiny jets, one of which controls the idle, so when it's clogged, you don't idle. The atomizer is not really visible when you dislocate the carb.

You can in fact access the atomizer in two steps, once the main jet is unmounted:

1. Unscrew the atomizer support at the far end of the main jet tube with a flathead screwdriver

2. Release the atomizer itself by pushing on top with a non-metallic object to make sure you don't damage it.

I just unmounted my atomizer tonight and the idle jet was completely clogged. In fact, it was even hidden below a thick white deposit... No wonder why the idle did not work in my case... I am cleaning it tonight and testing tomorrow, I hope that was the only issue with idle...

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