80 Moby Carb questions

Pat Finley /

I was hoping for some help from the experts out there.

Finally got my Moby to start after many years. But there must be a fuel flow problem because it won't idle. I took apart the carb and throughly cleaned it, but I must have screwed something up with the choke.

Part of my problem is that my choke cable is severed. So, I am not able to "choke" when attempting to start it. So, I guess I can't tell if the carb is blocked because it may be that I need to 'choke', but I can't. I don't really know what the choke is supposed to do, so that's another part of my problem. (I only know that you typically start the moped with choke action.)

After cleaning the carb, I must have put the choke back together improperly because fuel is leaking out the bottom. Anybody know how it goes on an '80 Moby? I know that somehow the cable comes in from the bottom of the carburetor and applies some sort of pressure that opens a valve - I think. I'm working with 3 pieces, a brass piece with a hole the width of the tension cable, a spring, and a white plastic piece (also with a hole the width of the tension cable). I can't seem to: figure out how to set these 3 pieces to get tension, and, what the choke is actually supposed to do.

Anybody want to help?

Thanks much..

Pat Finley

Re: 80 Moby Carb questions

Ron Brown /

Pat,

I will give this a try, even though your description does not correlate with the carbs on my two '79 Model 7s or my shop manual.

As far as I know, there are only 2 types of choke. One is a mechanism which blocks the air intake to the carb with a flap or shutter, creating increased vacuum in the venturi and increased gas flow through the main jet. The other is an extra passage for fuel to flow into the venturi when opened by raising a sealing plug from the starting fuel supply.

My carbs and I think yours, are of the second type, however, I have never seen one of these operated by a cable which enters the carb fro the bottom. They are usually controlled by a cable which enters the top of the carb, just to one side of the throttle slide.

Look carefully at the parts you have. The hole into which they fit, should have a raised "seat" around a hole in the bottom of it. The brass slug should have a rubber insert in one end of it with a matching indent caused by pressing on the seat. This piece goes in the hole first, rubber end first. The spring normally seats in the outer end of this slug to apply pressure for sealing when the choke is off. You have me on the plastic piece, it could be an alignment piece for the top of the spring but unless someone else posts, you may have to figure this out by figuring out where it fits best. This assembly is then held in place by the top of the carb.

Your fuel leak is most likely caused by the needle and seat vontrolled by the float. Make sure that the float does not have a leak (fuel inside it), that the pointed end of the float shaft and the seat in the top of the carb are clean and in good shape and that you install the float with the pointed end up. Sorry about that last obvious one, but apparently, several people who post here have had that problem.

If you stop the fuel leak, you will neeed to fix the choke to start it. You should be able to make a cable from a 10 speed gear change cable.

Good luck,

Ron

Re: 80 Moby Carb questions

Pat Finley /

Ron,

Thank you for your help I have tried to attach the picture from the Moped manual for the 50V. (It's on the same page as the display in the manual showing your model '7' carb.) Clearly the picture in the manual shows the cable coming in from the top as you described - but oddly enough, I really don't think mine worked that way most recently. (Maybe a mechanic tweaked things at some point in it's life, I don't know.) I don't have the rubber piece you are referring to, but I may have had it and lost it. The white plastic piece I am referring to does not fit all the way into the opening from the bottom, so it might be the bottom seat.

Anybody have a clean digital shot of a 50V carb? I have one from before I took it apart and I will post that tonight for your to see. Thank again Ron.

I'll give it another shot...

Pat finley

21.jpg

Re: 80 Moby Carb questions

Ron Brown /

Pat,

It looks like you have the same carb as me, just different intake and air cleaner.

The rubber I was refering to, I think is peened into the end of the brass slug although I could be thinking of a different carb. I don't recall any means of accessing the choke from the bottom other than maybe driving out a plug of some sort. I would think that if you can see through this area from top to bottom, you really have a problem.

Hopefuly, someone with a carb in hand will try to help, if not, I will pull one of mine and try to describe the mechanism in detail.

Ron

Re: 80 Moby Carb questions

Ron,Pat,I've got a Motobecane 50V manual here.What do you want described?I'll help if I can.

Re: 80 Moby Carb questions

Ron Brown /

Don,

I have a manual too, unfortunately, Pat seems to have a carb with a hole below the enrichener/choke that he thinks the cable used to go through. What we need is for someoune with a carb in thier hand to describe the choke mechanism in detail, including whether there is any kind of removable plug below the choke.

Ron

Re: 80 Moby Carb questions

Okay,Ron! Just in case I'll look anyway.A picture's worth a thousand words....sometimes.

Re: 80 Moby Carb questions

Ron Brown /

Don,

Go ahead, but it seems that Pat's carb has been disassembled or modified past any removable parts shown in the exploded view. On the other hand, if you would like to pull your carb so I don't have to.... : )

Ron

Re: 80 Moby Carb questions

Okay,guys! Just a thought from the manual troubleshooting guide.It says: Engine will run but won't idle : Throttle slide facing wrong directionCould that be it,Pat?

Re: 80 Moby Carb questions

No,I'm still kicking myself for selling that fine 1980 Moby.Big,tough bike with the big,comfortable seat.You won't see me badmouthing Motobecanes.But I like the Motobecane Sebring the best!

Re: 80 Moby Carb questions

Ron Brown /

Don,

I don't even know how you can do that, I am fairly sure there is only a groove in one side for the key. Aside from that, he has gas pouring out of the carb and apparently, a hole right through the carb where the choke installs.

Ron

Re: 80 Moby Carb questions

Yeah,Ron,I was wondering about that.But it's in the troubleshooting guide so I thought I'd post it.You see,I didn't learn much about my Moby `cause I sold it too quickly.Should've kept it.I'll keep looking.

Re: 80 Moby Carb questions

Well,Ron,the more I look at this picture,the more I think Pat's confusing the bottom fuel jet assembly with being a cable connection.If that top screw that accepts the cable end threads into the same threads as the bottom jet,I could see how he may have gotten confused.Other than that he must have a maverick carb.What do you think?

Re: 80 Moby Carb questions

Ron Brown /

Don,

At this point, I would believe anything. Pat says he is going to post a "before" picture tonight so maybe that will help. I suppose that if the threads are the same, you could screw the main jet in the rop and the choke in the bottom. Certainly would cause one hell of a leak.

Ron

Re: 80 Moby Carb questions

Yup! Better wait for the pic ,I guess.You'll have to help him if it's after 7pm `cause I'll be offline `til 7am after that.

Re: 80 Moby Carb questions

Pat Finley /

Ron and Don,

Thanks for your help. I should caution you that I am really a neophyte with this carb. I may be confusing the throttle and the choke even. I will post my "before" picture tonight. But just for clarification until then...

The part that I am trying to describe as the choke is the piece to the far right as you look at the picture in the manual (the attachment I posted).

What I am referring to as the

Re: 80 Moby Carb questions

Simon King /

Yeah, it's only supposed to fit in one way because of the groove in the throttle slide. However, I have two Motobecane's, and both of them have that groover broken off. In fact, oddly enough, I have a Moby that will only run when the slide is in backwards. Obviously that's pointing to some other gas / air issues though.

Ive also had good luck getting Moby's to run without the choke at all, so I'm guessing that his problem is the throttle. Motobecane carb is a tricky one.

Re: 80 Moby Carb questions

Ron Brown /

Pat,

Lets start from the top and go through the throttle assembly, then you can tell us what is left over and how you manage to get a cable into the bottom of the carb.

Bear with me if I am repeating what you said. I am just trying for clarification.

I think your carb has an extra bowl with a fuel filter in it. I am ignoring this because I don't have one and it looks strait forward enough to assemble from the manual.

With the carb body in your hand, if you look in the big hole in the top, you are looking down on the opening (venturi) where the fuel and air mix on thier way to the engine. In the bottom center of this opening is a small brass diffuser, if you were to drop the slide into the big hole, it would sit on top of this. If the diffuser is removable (some are, some are not), it is installed from the bottom of the carb and held in place by a small brass screw with an axial hole through it. Access to this screw is by removing the main jet (if you see no screwdriver slot after removing the main jet, your diffuser is not removable). This screws into the bottom of the carb, directly below the diffuser. It has a hex end visible on the outside of the carb, a narrowed section with a hole drilled radially through it, then a threaded section with a very small hole drilled axially through the threaded section to the cross hole.

Make sure this assembly is together correctly, it really only goes one way.

In operation, fuel flows from the float bowl to the narrow area of the main jet, into the cross drilling, then up through the small hole which is actually the main jet, to the diffuser.

From the top of the carb, the top cover with the gasket and o-ring, spring and throttle slide should be assembled to the throttle cable. The top of the carb can now be fitted, Making sure that the cut away on the bottom of the throttle slide faces away from the engine. Try the throttle control while looking through the veturi to make sure it closes almost completely and opens all the way.

At this point, you have only choke pieces left over and I hope, not too many holes in the carb to fit them into.

Try to describe these pieces and where you think you are going to put them in the carb.

By the way, I think you have identified the choke correctly in the picture, but as you can see, this has the cable on top.

Ron

Re: 80 Moby Carb questions

Pat Finley /

Ron,

I am at work, so carb is not in my hand. However, I am very confident that the portion of the carb you described in detail above is installed correctly. You have exactly identified the carb and it does have an extra fuel filter as well. The diffuser is removable and is in place just as you described.

The only 'choke' parts I have left are a spring, a white plastic piece with a hole in it the size of the tension cable, and a brass piece that also has a whole in it the size of the tension cable. I also have a brass washer that I thought was to be used to secure the end of the choke tension cable to the TOP of the carburetor. I know this must be wrong. I'll be home in an hour and will get a better description of the pieces.

Thanks, Pat

Re: 80 Moby Carb questions

Pat Finley /

Ron,

I am at work, so carb is not in my hand. However, I am very confident that the portion of the carb you described in detail above is installed correctly. You have exactly identified the carb and it does have an extra fuel filter as well. The diffuser is removable and is in place just as you described.

The only 'choke' parts I have left are a spring, a white plastic piece with a hole in it the size of the tension cable, and a brass piece that also has a whole in it the size of the tension cable. I also have a brass washer that I thought was to be used to secure the end of the choke tension cable to the TOP of the carburetor. I know this must be wrong. I'll be home in an hour and will get a better description of the pieces.

Thanks, Pat

Re: 80 Moby Carb questions

Pat Finley /

Here is the first of two pictures I said I would post.

Please note the end of the tension cable for the choke on the top of the carb...

Pat

Moby3.jpg

Re: 80 Moby Carb questions

Pat Finley /

Here is another view...

Moby4.jpg

Re: 80 Moby Carb questions

Pat Finley /

The pictures I posted are of the Moby fully assembled before I took it apart and cleaned it. I am the only owner and before I shelved it for 8 or so yars, it ran fine with a operating choke with cable coming from the bottom of the carb. So, I'm sort of wondering if a mechanic somewhere along the line did jury-rig my choke, or, did Motobecane change something in 1980 that wasn't reflected in their manual.

Re: 80 Moby Carb questions

Ron Brown /

Pat Finley wrote:

>

> The pictures I posted are of the Moby fully assembled before

> I took it apart and cleaned it. I am the only owner and

> before I shelved it for 8 or so yars, it ran fine with a

> operating choke ..........with cable coming from the bottom of the

> carb........... So, I'm sort of wondering if a mechanic somewhere

> along the line did jury-rig my choke, or, did Motobecane

> change something in 1980 that wasn't reflected in their manual.

>Please note the end of the tension cable for the choke on the top of the carb...

Pat,

Where exactly do you think the choke cable is supposed to ENTER the carb?

Ron

Re: 80 Moby Carb questions

Pat Finley /

Ron/Don,

Here are the mappings for the 6 pictures I am attaching one reply at a time...

pdrm0304.jpg - Exploded view of carb taken apart. (Diffuser and related parts left in throttle assembly.) The four parts off to the right are what I have left to work with for the choke.

pdrm0307.jpg - View looking down from top of carb with top housing off. (From left, filter bowl, large float bowl, throttle assembly, hollow choke assembly.)

pdrm0309.jpg. - View of what I would refer to as top carburetor housing. You can see the main screw, throttle cable and slide etc. You can also see the top of the choke housing that is open on one side for feed of the missing tension cable. The choke housing is about 3/4" inch long and fits inside the choke assembly.

pdrm0310.jpg. Another view of the "top carburetor housing" to show the choke housing better. You can see the throtte spring and slide in the background.

pdrm0312.jpg Closer view of the four parts I have left. The top piece looks like brass in the picture, but it is white plastic. The second piece is the brass piece I referred to in previous posts. The third piece is the brass "washer"? This is what WAS on top of the carburetor in my BEFOR DISSAMBLY picture I posted late yesterday. I'm confident this doesn't go on the top normally, but it was on top for the last ten years or so when my ped was shelved. The brass "washer" has a little ridge in it or natural o-ring and it fits flush with the bottom of the choke assembly on the carb. (Of course, the cable end has to cover the whole in the middle of the washer - so it seems like it would leak gas a little if there wasn't some other mechanism at the bottom of the assembly.

pdrm0313.jpg. Same as previous picture except brass piece is setting up so you can see that it is hollow.

I'm starting to feel somewhat confident that I am missing a piece that is suppossed to cover the top of the choke housing where the cable feeds into the choke assembly. Any ideas?

Pdrm0304.jpg

Re: 80 Moby Carb questions

Pat Finley /

pdrm0307.jpg - View looking down from top of carb with top housing off. (From left, filter bowl, large float bowl, throttle assembly, hollow choke assembly.)

Pdrm0307.jpg

Re: 80 Moby Carb questions

Pat Finley /

pdrm0309.jpg. - View of what I would refer to as top carburetor housing. You can see the main screw, throttle cable and slide etc. You can also see the top of the choke housing that is open on one side for feed of the missing tension cable. The choke housing is about 3/4" inch long and fits inside the choke assembly.

Pdrm0309.jpg

Re: 80 Moby Carb questions

Pat Finley /

pdrm0310.jpg. Another view of the "top carburetor housing" to show the choke housing better. You can see the throtte spring and slide in the background.

Pdrm0310.jpg

Re: 80 Moby Carb questions

Pat Finley /

pdrm0312.jpg Closer view of the four parts I have left. The top piece looks like brass in the picture, but it is white plastic. The second piece is the brass piece I referred to in previous posts. The third piece is the brass "washer"? This is what WAS on top of the carburetor in my BEFORE DISASSEMBLY picture I posted late yesterday. I'm confident this doesn't go on the top normally, but it was on top for the last ten years or so when my ped was shelved. The brass "washer" has a little ridge in it or natural o-ring and it fits flush with the bottom of the choke assembly on the carb. (Of course, the cable end has to cover the whole in the middle of the washer - so it seems like it would leak gas a little if there wasn't some other mechanism at the bottom of the assembly.

Pdrm0312.jpg

Re: 80 Moby Carb questions

Pat Finley /

pdrm0313.jpg. Same as previous picture except brass piece is setting up so you can see that it is hollow.

Pdrm0313.jpg

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