mobylette choke

ok i knw that if i have to hold the choke for the thing to stay on that means im not getting gas , right?

soooooo..... what the F@#$ do i do about it.

i have ripped this ped apart so many times and i am getting irritated and grouchy

Re: mobylette choke

you know.. you check and/or clean the entire fuel pathway from the gas tank's cap all the way to the engine ..

it could be slow fuel flow from the tank.. or just a tiny bit of crap in the float bowl.. a clogged filter somewhere.. Work your way from one end to the other, cleaning and inspecting, 'till you find out where the problem is.

Something like an old, deteriorating fuel line and/or broken filter screens might clog it up again in the future so.. well.. if you wanna spend more time riding, do it right and you won't have to do it again.

Re: mobylette choke

Mike Scouty McScoutington /

the jet on a gurtner carb is kinda funny and prone to cloging. do a good clean of the jet.

Re: mobylette choke

ok ill clean it out again.

it is strange cause i just put in a new fuel shut off valve and fuel line when i cleaned the carb...

ill lcean the carb again, but is there anything else that could be doing this. not that i doubt what you are telling me.

when i am holding the choke it is closing or opening air or gas? i do not know. sorry if i sound dim

Re: mobylette choke

First describe exactly what's going on with that bike..

Does it start up ok (with the choke closed)? But then, when accelerating from a stop, does it go real slow and sputter and/or die unless you keep the choke closed. How fast does the bike go if you do leave the choke closed?


Closing the choke makes the mix richer than it would be with the choke wide open.. less air is allowed in to mix with available fuel.

So, if fuel is restricted, closing the choke forces the carb to use less air in the mixture.. And this somewhat corrects the mixture's fuel:air ratio.

At lower engine speeds a rich (lots of fuel compared to the amount of air) mixture is needed to run.. at higher RPM the carburetor (normally) leans the mix automatically.

Re: mobylette choke

_ "Does it start up ok (with the choke closed)? But then, when accelerating from a stop, does it go real slow and sputter and/or die unless you keep the choke closed. How fast does the bike go if you do leave the choke closed? "

that is exactly what happens. when it does go it picks up pretty quick and it hits a little over 20 but i think it would go faster if i could hit a long stretch of road.

Re: mobylette choke

it does sound like not enough fuel (compared to the amount of air) is getting through the carburetor and into the engine.

The closed choke restricts air intake and "corrects" the mixture.

So, if fuel is now getting into the float bowl, the thing to check for is a clean float bowl and that the main jet's hole is open and clear. A tiny bit of floating crap will get sucked up and partially clog that jet..


Lean = lots of air compared to fuel..

Rich = less air or more fuel in the mix.. same difference..

Fuel mixture:

A 1:10 (fuel:air) means 1 pound of fuel to 10 pounds of air. (it's measured by weight .. a lot of air weigh quite a bit..)

A 1:3 mixture is much richer than above.. (only 3 pounds of air instead of 10 pounds of air is mixed with that same 1 pound of fuel.)

1:14 ... this is leaner than both the others.. a larger amount of air (14 pounds) is being mixed with that same 1 pound of fuel


When starting the engine needs a very rich mix, like 1:2 or 1:3.

Idling requires less fuel and more air (leaner) like 1:8 or so. Normal running is leaner still.. somewhere around 1:13.

Re: mobylette choke

cool thanx for all the info

ill blast out the jet and check the float bowl tomorrow and post the results

Re: mobylette choke

See Ya Moped Army /

If you're tank is full of gunk and rust, it will impede the flow of fuel through the petcock. Even though you have a new petcock, if the tank is dirty it will clog up quickly.

Re: mobylette choke

ok i was tinkering this afternoon and noticed that the brass screw on the bottom of the carb is pissing out gas!!!

when i shut of the flow there is no leak but when it is on there is a good steady stream.

now i am able to get the bike going, aside from this new prob., but it dies when i am not pulling the throttle open. probably the idle but i will check that tomorrow.

Re: mobylette choke

could this problem be a faulty float???

i was just reading that if the float is junk then the fuel will leak out from a overflow drain thing, could this be the brass screw at the bottom of the carb???

Re: mobylette choke

sure could.. or for some other reason the fuel level in the float bowl is too high.

Remove the float bowl.. is there a long thin vertical tube sticking up inside? That would be the overflow tube.

And if fuel level goes above the top of that tube, fuel will drain out of the drain-screw hole at the bottom of the bowl.

Re: mobylette choke

how do i fix that?? new float

(that is the plastic ball with the needle correct?)


Re: mobylette choke


If this is a Gurtner carb, the brass screw at the bottom is actually the main jet. It relies on a metal-to-metal seal to keep the fuel from leaking out.

Either the jet is not sealing up properly, or you have a leak somewhere above it, that is dripping off of the jet, and making it look like it's leaking.

Re: mobylette choke


if the jet is leaking (it is a gurtner) what do i do?

i know i need a new one but what is the size, if you know it off the top of your head?

also if i am putting in a new jet but could i get one to let more fuel in, would that do anything?

Re: mobylette choke

i dunno anything specific.. But a float bowl always has something in it that floats.. a ball? i guess so.

Whatever it is.. It floats upwards and pushes on a little valve-thing near the float's pivot hinge. That valve then shuts off fuel. Fuel can no longer enter the bowl until some fuel is used by the engine.

That drops fuel level and the float drops and the valve opens again.. and a little more fuel is allowed into the bowl.


The float-ball-thing might be ok. The little float-valve itself might be leaking. In fact, it's far more likely that the valve is leaking.

Look closely at the valve's tip (probably a black plastic tip) Is it's sharp tip scratched or worn over or does it have a groove around it? If so you probbly need a new one. The valve tip must be perfect.

If the float-valve's tip looks ok, the valve-seat (up there where the tip fits into) might be damaged or dirty.

Re: mobylette choke


rock, i'll check that out. i hope that it is just dirty or something...

Re: mobylette choke

got the beast to run without the choke being held and got the leak to stop

the float seemed to be fine so i took out the screw on the bottom and there was no real seal in there.

so i made up a rubber gasket and put that in there and the leak has stopped.

does anyone think that this could f anything up?

once i put the rubber piece in there the ped idled pretty well and didnt crap out and like i said it stoped the leak

Re: mobylette choke


Fact is, the Gurtner is and always was a cheap carburetor. This was fine when they were in production, as it was inexpensive to get parts, or just replace it outright. These days, the problems are more apparent. I don't think they were ever meant to last 30+ years.

You're right - there is no sealing gasket on the jet - it just relies on a proper fit between the brass jet and potmetal carb body. This is fine once or twice, but with repeated disassembly, it can fail. Even the British would have had the sense to use a fiber washer in this area. What you did should work just fine; I would have tried a little teflon tape in the sealing area, but whatever works here is fine.

Re: mobylette choke

so if the carb isnt great and coould easily be replaced what would you suggest as a good replacment??

Re: mobylette choke

a puch, haha, just kidding.

Re: mobylette choke

well my next project is a severly beaten down puch newport so well see if it is easier to get going haha

Re: mobylette choke


Considering the time and cost involved in finding a different carb, fitting it, getting the cables working and finally tuning it - I would just keep putzing with the Gurtner.

In the meantime, keep your eyes open for a new or slightly used carb. If you find one, just throw it on the shelf - so you have it if you need it.

Re: mobylette choke

good idea!

thanx for the advice brotha'

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