Moby just started maxing out at 10mph

Aidan Avery /

Hey y'all, I have Moby 50V with a 65cc in it. Everything has been running smoothly since I bought it a few months ago. I even had it tuned up a month ago, just to make sure everything was tip top. It was running great after.

I took about two weeks off from riding while I was moving down to Arizona. In that time two things happened:

-It sat in the back of a UHaul (snug and upright), where it undoubtedly got really freaking hot.

-Today, as I was taking out for my first ride since the move, the wind blew it over. I picked it up quickly, didn't seen any aesthetic damage, but who knows?

Then when I started riding... 10mph max. Usually this guy goes upwards of 30.

I'm not much of a mechanic at all. I don't know the ins and outs of my moped, but I love this thing and I wanna what I can do get it back to the fun ride that I know it is. Where do I start with a problem like this?

To note: Starts up completely find. It SOUNDS like it's giving a lot of gas when I fully crank the throlled, but the bike is just not responding like it did before. Just idling down the street. There is some clicking which may be new as well.

Thank you.

Re: Moby just started maxing out at 10mph

Where'd you move from? What's the elevation difference silly goose? Sounds like you went from sea level to mountain level or something. You're gonna need to downjet, there's not enough oxygen in the air compared to wherever you moved from for how much fuel delivery you have currently

Re: Moby just started maxing out at 10mph

Aidan Avery /

Hey, thanks for the reply!

I moved from Portland to Tucson. Some quick googling tells me I increased about 2,200 ft in altitude. Does that sound like an amount that would cause the issue to you? What exactly is downjetting? Think it might be my solution?

Sorry, I'm a bit inept at this moped thing. I'm learning as I go, but this is all new to me. (edited)

Re: Moby just started maxing out at 10mph

Kilian Münscher /

Down jetting means putting smaller jets in the carb for less fuel delivery

Re: Moby just started maxing out at 10mph

2,200 ft elevation and it’s probably hotter in Tucson as well. Both make the air thinner.

Does your bike act rich? Four stroking and such? If so, you could pull your air filter off for a test to see if it helps. If it does, put the filter back on and down jet.

If it isn’t four stroking (and I think it would be bad if you’re limited to 10mph) then do not ride it until you check for air leaks.

Re: Moby just started maxing out at 10mph

If the only variable changed was the altitude and climate then it's 100% the jetting. Put a smaller jet in the carb and blast.

Re: Moby just started maxing out at 10mph

I'd check the carb for anything that might be out of place .

Sure , jetting might have a small effect , but not a 20 MPH effect .

I run my FA50 the same on the gulf coast as I do in the mountains , no jet changes .

It runs fine .

Re: Moby just started maxing out at 10mph

Aidan Avery /

Thanks for the input guys.

@PD. This afternoon I will give the bike a closer inspection. I don't know what the carb is supposed to look like, so I'll need to do a bit of research to know if anything is out of place from the normal position.

@Nick and Papa. Okay thanks. Sounds like I'll need to look into that. Is it something I could do on my own provided I get all the parts and have a repair manual in front of me?

And, Papa, I just looked up what four stroking is. Let me run another test later today and get back to you about that.

@Kilian. Thank you.

Re: Moby just started maxing out at 10mph

Someone got a kick out of me describing four stroking as the Perry the Platypus sound.

Normal is: Errrrrrrrr

Four stroke: gr gr gr gr gr gr

Re: Moby just started maxing out at 10mph

Aidan Avery /

Haha great, I'll listen for it. And would it be all the time? Just while I'm throttling hard? Just while I'm idling?

Now that I think about it I was actually recording a video while I took it riding (or tried to) yesterday, so I assume that should be enough to show if it's four stroking or not.

Re: Moby just started maxing out at 10mph

Aidan Avery /

Here's footage of it from yesterday. The audio is a bit muffled because the camera was in a plastic protector. If it's not clear enough to determine anything I can get better audio either today or tomorrow.

Re: Moby just started maxing out at 10mph

You're four-stroking like crazy. Downjet

Re: Moby just started maxing out at 10mph

Aidan Avery /

@Nick. Alright, thanks for checking it out. Is this something someone with limited mechanical experience can feasibly do? Or will I need to take it to someone?

Re: Moby just started maxing out at 10mph

You might try raising the slide needle clip to the top notch .

Here's a manual :

https://drive.google.com/drive/folders/1xzSqebrL4bLYS5pPZlUlB_Hta2bLoNWC

page 16-1 shows the slide needle ...

Re: Moby just started maxing out at 10mph

> Aidan Avery Wrote:

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

> @Nick. Alright, thanks for checking it out. Is this something someone

> with limited mechanical experience can feasibly do? Or will I need to

> take it to someone?

It is extremely easy on a Gurtner carburetor, which you have (assuming you have the stock carb)

You literally just need a flathead screwdriver. If 13 year old me could do it, you can too. Use the wiki, it has literally everything you could possibly need to know about your bike on it.

Re: Moby just started maxing out at 10mph

Aidan Avery /

Awesome, thank you both very much. I will look into this when I get off work today.

And I believe I have the stock carb, the only major thing that's not stock is the 65cc.

Re: Moby just started maxing out at 10mph

Aidan Avery /

@PD

Hey that link took me to some Honda manuals. Did you intend to do that, or did you mean to link one for a Moby?

Re: Moby just started maxing out at 10mph

Aidan Avery /

Update:

I have figured out that I actually do have a replaced carb. A Dellorto SHA. Looks like it should be likewise pretty easy to change the jet. I'm going to get a flathead today and open it up and see what size the current jet is and then order a smaller one.

Once I've got that done I'll report back with results.

Thanks again a lot to everyone who responded so far.

Re: Moby just started maxing out at 10mph

> Aidan Avery Wrote:

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

> Update:

>

> I have figured out that I actually do have a replaced carb. A Dellorto

> SHA. Looks like it should be likewise pretty easy to change the jet. I'm

> going to get a flathead today and open it up and see what size the

> current jet is and then order a smaller one.

>

> Once I've got that done I'll report back with results.

>

> Thanks again a lot to everyone who responded so far.

Awesome, SHA's are significantly better than gurtners and as you said almost as easy to change the jets on.

Re: Moby just started maxing out at 10mph

before u downjet,make sure your choke is working, that your float needle is sealing off gas flow and your throttle cable is outside the spring, all which would make it run rich.

Re: Moby just started maxing out at 10mph

65cc AV7 - what carb SPECIFICALLY do you have (SHA 14:12 14:14 15:15...whatever)

Is it on a stock bendy restricted intake?

Is the exhause completely stock?

What is your timing set at?

Have you read the plug? (no you dont have to cut it open. illustration is to give you the idea)

BasicPlugReading1.jpg

Re: Moby just started maxing out at 10mph

Good call on switching to the Dellorto. Did it on my buddy’s and he went from 20mph to 30mph. Also, try taking the exhaust off the moped, and take the nut off the end of the exhaust and pull it apart. Then, take a plumbing pipe cleaner(or a coat hanger) and go to town on that fucker. Sometimes they get clogged up with carbon and it ends up pushing some air out of the intake, making it almost impossible to pull in fuel.

Re: Moby just started maxing out at 10mph

> Aidan Avery Wrote:

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

> @PD

>

> Hey that link took me to some Honda manuals. Did you intend to do that,

> or did you mean to link one for a Moby?

Ha. Sorry about that^ . I don't know what happened . Wrong button maybe .

Anyway , here's a link to Moby manuals :

https://drive.google.com/drive/folders/1XZIGaODutDY-NlVuGu-7WwoZTPyHWxPk

Re: Moby just started maxing out at 10mph

Aidan Avery /

Update: talked to Sabatino in portland (love that shop) who initially installed the new parts a few years ago and saw the moped as recently as a month ago. He likewise suggested downjetting due to the elevation change.

So, I got the carb out, got a look at the jet (78), and ordered various other jets from Treatland (70, 72, 74, 76). Going to try the 74 first, as per Sabatino's recommendation. All in all, feeling somewhat accomplished so far considering I have zero prior mechanical experience.

@rebel. It's the dellorto 15. And I'm sorry to say that I don't know the answers to your other questions since I'm not well versed in mechanics. But you can see the moby and some info here: https://www.sabatinomopeds.com/product-page/1978-motobecane-50v

@dillon and @pat: I appreciate the recommendations. I'm gonna downjet first, since Sabatino seconded that idea and because I want to limit how many variables I'm messing with at any one time, especially because this is all new to me. Will report back and, if downjetting doesn't do the trick, begin considering other possible options.

@PD thanks! I'll check'em out.

BAD NEWS: fractured my hand in a bicycle accident yesterday. Definitely going to impede progress on both the project and riding for a bit :(

Re: Moby just started maxing out at 10mph

YIKES AND OUCH - sux to have a injury to slow the progress...

Take off the side cover and look if the carb is on a shorty intake or a longish pipe with a bend so the inlet of the carb is facing the right side of the bike. If it is the one facing the side then it is a original bendy and it will give you troubles tuning because it necks down to 13,8mm in the bends.

15:15 sha - fit a 11/16 X 13/16 X 1/16 oring between the carb and the intake to ensure a goodly seal. If it is a 15mm intake then look see if it necks down where to goes from round to rectangle bore inside. Needs to be straight through for better and easier tuning.

Leanest I will go on a 70cc kit is 74 so that size should be close, but keep the fatter ones handy because once she is running better you will need them because you really need to derestrict the exhause as well. That 8mm ID exit pipe is killing any potential to make power with the over bore cylinder and bigger carby. Do not go straight through or pipe-less because that will quickly mess up the engine, but try a exit pipe 10-11mm ID. If you have down time from riding you will have a chance to experiment with making a replacement backing plate for the exhause. Duplicate the factory exit plate and pipe with a 10-11mm ID pipe but 1/2 the length inside the muffler as the stock pipe so it bypasses the long way out.

> Aidan Avery Wrote:

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

> BAD NEWS: fractured my hand in a bicycle accident yesterday. Definitely

> going to impede progress on both the project and riding for a bit :(

Re: Moby just started maxing out at 10mph

Aidan Avery /

Just wanted to report back that a few weeks ago I finally got the chance to get to work on this. Downjetted to a 74 (as per Sabatino's recommendation). It was my first time doing any real work on a vehicle, but with a combo of Sabatino/MopedArmy/Youtube, I got through it smoothly. I feel pretty proud, even though it was only a minor mechanical operation.

Anyway, all is well now! The motobécane runs as good as it did up in Portland. Back up to 33ish MPH on flatground. I went for a 10 mile or so ride today, with a pitstop to pick up some pizza along the way. Great fun!

Thanks for the help everyone. Mopedarmy rocks!

Re: Moby just started maxing out at 10mph

Excellent success story!

Re: Moby just started maxing out at 10mph

Huzzah!

Re: Moby just started maxing out at 10mph

Running moped + pizza = winning

Re: Moby just started maxing out at 10mph

Excellent news

« Go to Topics — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account