Carburetor adjustments

So I finally kind of finished my moped. It runs pretty well but not great. She does 26 mph but I'm pretty sure it can do 30. She idles really fast and runs hot. I started spaying brake cleaner around the seals and gaskets to see if I have any leaks then I sprayed at the carb filter and she really slowed down and idled really nice. So I'm thinking I either need less air or more fuel. . I have a Sha 15.15 with a 70 jet and I removed a couple of screens from the carb and deresticted the exhaust. The other issue I'm having is that turning the handlebars also affects the idle. The cable is not tight is there a fix? Let me know what you think . Thanks

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Re: Carburetor adjustments

Cable is probably too tight or routed improperly and you probably don't have the rubber seal in the carb to seal it on the intake.

Re: Carburetor adjustments

Intake is sealed with an o-ring.

Re: Carburetor adjustments

> Joe F Wrote:

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

> Intake is sealed with an o-ring.

Make sure your throttle cable isn't too short holding the slide open making it idle high if the idle screw doesn't idle it down.

Re: Carburetor adjustments

Russell Huddy /

70 jet is pretty high for that set up.

Sounds like you have an air leak to me but you need to sort out your cable issue first.

Re: Carburetor adjustments

If it is an old cable it could be frayed and binding up somewhere. If it is a new cable, be sure it is routed correctly.

Re: Carburetor adjustments

mbk cables are tough. the cable is def to short/maladjusted. let me guess, you turn the bars to the right and it revs?

you'll need to notch the throttle tube to get all 15mm of pull, i just did this today on a le moped. otherwise, the option is high idle & racing when the bars are turned to the right just to be able to release the choke lever if its a click choke carb.

Re: Carburetor adjustments

Pushrod Fifty /

I like the seat, looks cool.

Re: Carburetor adjustments

Checked for leaks the chemical way carb, brake and propane. Nothing conclusive. The only thing that I forgot to mention was I didn't have my choke cable installed. I fixed the handlebar / throttle issue by loosening the cable. I also put a 68 jet. It got up to 28 mph I sure it could do better. Anyone with a motobecane who knows exactly what the idles rpms are supposed to be.

Thanks

Re: Carburetor adjustments

Pushrod Fifty /

They idle smooth when tuned. You have to look at the plug to see if its running lean or rich. You could have an ignition issue, old condenser, dirty points, bad plug.

Re: Carburetor adjustments

Russell Huddy /

That set up should only be running around a 58 jet. It’s leaking some where

What are you calling hot? What’s your head temp?

Re: Carburetor adjustments

I'm not sure. What do you guys think. At the moment I'm running a 68 jet

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Re: Carburetor adjustments

Get a new plug and redo the chop. It looks like that one has been baked on both ends and wont give you a very good read off it.

Re: Carburetor adjustments

Mike Scouty McScoutington /

I ran the same setup like 15 years ago and I was either a 56 or 58 jet and was in the lower mid 30s. I cannot stress enough lengthening the cutout in the throttle tube. Did you cut the engine spring stop when you put the variator on there? If you you won't be able to fully open the variator and will limit your top end

Re: Carburetor adjustments

> Mike Scouty McScoutington Wrote:

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

> I ran the same setup like 15 years ago and I was either a 56 or 58 jet

> and was in the lower mid 30s. I cannot stress enough lengthening the

> cutout in the throttle tube. Did you cut the engine spring stop when

> you put the variator on there? If you you won't be able to fully open

> the variator and will limit your top end

Engine spring stop? Can you clarify I am uncertain of what you're talking about. I lengthened the throttle cutout

Re: Carburetor adjustments

So guys I dropped my jet size down to 62. Everyone kept saying that my jet was too big and that with my setup I should be using a 56/58 jet. At 62 it's lean. I wondering if having deresticted the exhaust and removed two filter screens would have that effect ? I've made a few runs and after having worked on the throttle I've gotten the moped up to 50 kph roughly 30 mph. It runs and idles well but no matter how much work I put on the throttle it won't open the slide all the way, it stays closed approximately 3mm. I don't think it will ever get any better. I've done all of the mods Rebel Moby specifies for getting the throttle to work with the 1515 Sha. What would be the best aftermarket throttle for this moped some thing without to many workarounds ? Has anybody installed maguras that also have the brake switch's?

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Re: Carburetor adjustments

Pushrod Fifty /

64 should be spot on. The first plug you showed looked like it came out of one of my good running bikes.

Re: Carburetor adjustments

Mike Scouty McScoutington /

I don't want this to be taken the wrong way, but you're sure you're filing the correct side of the groove in the throttle tube right?

As for the engine spring I was talking about before, I mean this guy

https://www.treatland.tv/motobecane-engine-tension-spring-STOPPER-bracket-p/mbk-tension-spring-stopper.htm

The Moby 40 came stock with a dimoby clutch which has a very small window in the stop bracket. If you want your variator to open all the way you need to cut the spring stop to look like that one.

Re: Carburetor adjustments

> Mike Scouty McScoutington Wrote:

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

> I don't want this to be taken the wrong way, but you're sure you're

> filing the correct side of the groove in the throttle tube right?

>

> As for the engine spring I was talking about before, I mean this guy

>

> https://www.treatland.tv/motobecane-engine-tension-spring-STOPPER-bracket-p/mbk-tension-spring-stopper.htm

>

> The Moby 40 came stock with a dimoby clutch which has a very small

> window in the stop bracket. If you want your variator to open all the

> way you need to cut the spring stop to look like that one.

Yes pretty sure. Followed Moby's explanation to the letter. The problem is the little ledge in the pic it's stopping the throttle from traveling any further. Now I understand the spring thing. My Moby came with a variator it's a 40v.

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Re: Carburetor adjustments

> Pushrod Fifty Wrote:

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

> 64 should be spot on. The first plug you showed looked like it came out

> of one of my good running bikes.

Thanks I'll try that. Ran out of plugs, I only have colder plugs I wonder if that would change the outcome of the plug chop?

Re: Carburetor adjustments

Mike Scouty McScoutington /

Couple things you can try with the throttle. First adjust your cable so when the throttle is backed all the way off the knarp is all the way against the assembly. That will set you at a good zero point. If that adjustment is off you won't be able to get the full pull of the assembly. If that still doesn't open the throttle slide all the way knock that lip down so you gain the necessary travel.

Re: Carburetor adjustments

68 to a 62 is a big jump. I would have tried a 66, then a 64, and finally the 62. Seeing it too lean would move me back up, or possibly add back the screens I removed. It is time and trial and error to figure it all out. You seem to be making progress for sure!

Re: Carburetor adjustments

Pushrod Fifty /

Keep the same heat range so you can follow your changes one at a time.

Re: Carburetor adjustments

SHould be jetting around 64 if there are no leaks, perhaps the spi seals are no longer sealing as well as they should, I would suggest to give it a proper leakdown test rather than phoquing around with spraying shyte around the engine looking for a leak.

Look down the throat of the carb and crank the throttle, check that WOT is actual wide open at the carb, if you see any of the slide then it is not quite there yet and a little can make a big difference.

Dont mess with heat range on the plug. You can reuse a old plug to do a chop, just clean it with a brass brush and regap the plug, 0,40mm same as setting on the points gap.

What is the timing set to? Try 1,5mm BTDC and make sure the contact gap is at 0,40mm at index.

Re: Carburetor adjustments

Cool thanks for the info. I've really massaged that throttle, just worried about going any further without going to far. I've added the additional travel to the throttle but it doesn't reach the limiting set screw. The lip on the outside of the throttle stops it from reaching that set screw. By the way I see things I'm running the risk of have the throttle getting stuck behind the decompression tab and staying stuck open if I decided to remove the lip on the outside. It was suggested that I advance the throttle cable set screw all the way forward but that would render the decompression valve useless and there would be no way to stop the engine. I haven't hooked up the kill switch yet. The Treats parti cdi is set to 1.5 mm btdc and the plug gaped at .40mm. I've checked for leaks and all seems well. I haven't used the real method you've suggested but I will. I going to try porting over the winter with your tutorial so at that point I'll be changing all the seals, gaskets and bearings. I hope all of this makes sense thanks.

Re: Carburetor adjustments

Oh - CDI - then set timing at 1,2mm BTDC

Indeed you do not want to over work the cursor, but there should be enough space for you to get even more than 15mm travel. Did you install the cable with all of the adjusters screwed all the way in (obviously every mm counts) ?

> Joe F Wrote:

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

> Cool thanks for the info. I've really massaged that throttle, just

> worried about going any further without going to far. I've added the

> additional travel to the throttle but it doesn't reach the limiting set

> screw. The lip on the outside of the throttle stops it from reaching

> that set screw. By the way I see things I'm running the risk of have

> the throttle getting stuck behind the decompression tab and staying

> stuck open if I decided to remove the lip on the outside. It was

> suggested that I advance the throttle cable set screw all the way

> forward but that would render the decompression valve useless and there

> would be no way to stop the engine. I haven't hooked up the kill switch

> yet. The Treats parti cdi is set to 1.5 mm btdc and the plug gaped at

> .40mm. I've checked for leaks and all seems well. I haven't used the

> real method you've suggested but I will. I going to try porting over the

> winter with your tutorial so at that point I'll be changing all the

> seals, gaskets and bearings. I hope all of this makes sense thanks.

Re: Carburetor adjustments

I recently purchased a 1978 Puch Newport L. It had not been taken very good care of and had not been operational for a while. I have begun restoring it and are now in the process of trying to get it to idle. I have tried what most of the posts have suggested to no avail. (cleaned the carb, adjusted the needle, checked for leaks, etc) Finally I bought a new carb which acts just like the old one. The engine will start and run if the throttle is held a good bit above idle but will die if the throttle is at or slightly above idle. This is the first experience I have had with a carb that has no pilot jet. Any help would be greatly appreciated. Gene

Re: Carburetor adjustments

Hello Kirby, congratulations with your new to you Puch. I wish I could be of more help with your problem but I would suggest that you start your own post. Members here familiar with Puch mopeds are less likely to find your post burried below my post with an image of a motobecane in the title. You will find that the members of the forum are super helpful if you can direct your questions to the right people. I would think that posting your questions in the repair section with a complete description of what you have done so far will get you the help you require. Good luck. I look forward to seeing your moped running properly.

Re: Carburetor adjustments

I’m following your thread as I have all new cables coming from Treats but this is how I got my lawnmower to run Sunday so I could mow. I won’t be doing anything like this to my 78 Maxi Luxe but I may be right behind you. Geez, I hope this thing runs right - you know - AFTER I “fix” it.

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Re: Carburetor adjustments

Holy Cow! That looks like a Bad way to start a Saturday morning.

But I'm Happy it worked and TU for the picture.

You're at the go to place for scooter help, be careful....

It turns into an addiction, you say just one more.

Then you pass a yard sale 🙂

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