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Subject: "Electric Choke for scooter/moped carburettors How does "    
Conferences > International New Scooter BBS > Topic #6614
Reading Topic #6614

radlam
Member since Nov-6-06
8 posts
Nov-07-06, 12:46 PM (EDT)
 
"Electric Choke for scooter/moped carburettors How does "
 
   Hi folks, forgive me if this topic has been covered before but I didn't see a search function which could zing me straight to the info.
I have a Beta Tempo 50cc I'm looking at which is a royal pain to start.

It has a choke that pushes into the top of the carb with wires trailing off into the harness, with a little clip/clamp screwed on to keep it in place.

Can anyone tell me exactly what exactly does it do?
(Apart from the seemingly obvious)

I looked very carefully at the carb and can see how air is drawn through it, particularly when starting with the throttle slide closed.

Trouble is, unless the plunger on the choke is forced up against its spring , away from the choke jet, by air being sucked through the choke plunger chamber, I can't see how else it works.

Most choke are just on, then off. A jet is oncovered then covered.

This choke plunger not only has the usual rubber tip to block the choke jet, but also a metering needle (similiar to a throttle slide) which leads me to think it gradually shuts off, after being open from a cold start.

With the choke removed from the carb but still connected to the harness on another bike (a Vespa 50) with the same choke system, I thought maybe switching on the ignition would activate some kind of solenoid which might draw up the choke plunger, which would uncover the choke jet, allowing gas to suck up it and through the drillings into the side of the carb venturi into the engine.
But it wouldn't move a millimetre.
This bike (a Vespa 50 scooter )starts fine though unlike the Beta Tempo.

If the suction method is true, does the "Electric Choke" then activate more downward pressure after a few mins to force it closed, thus preventing an over-rich mixture from continuing after the bike runs for a few minutes?

Trouble with that though is, the Tempo should start but run poorly when warm if the electric choke does not shut off.

I'm assuming the Electric Choke plays an active part in the starting process and then shuts off?

I think I can see what looks like quite a thick spring coil in the body around the inner end where the choke plunger protudes out, but what they do is a mystery to me too.

I remember a Suzuki CP50 used to have an expanding copper rod which when heated by the warming engine, pushed against another rod with an angle cut at one end. As the copper rod pushed against the slant it forced it to slide down against a spring, shutting off a hole stopping the air flow over the choke jet and thus the richer gas mix.

Is this some derivitive of that on the Tempo Weber carb?
Is there some heater element in the choke body?
Does the wiring connect only to a coil from the magneto/generator so the battery isn't in circuit with the Electric Choke?

I'm at the point of finding a wreck and cutting the wretched choke in half to figure it out if nobody knows.

Any help would be gratefully received.

Thanks, radlam




 

 
2pac
Member since May-22-04
110 posts
Nov-07-06, 05:08 PM (EDT)
 
1. "RE: Electric Choke for scooter/moped carburettors How d"
In response to message #0
 
   I believe the auto-enrichener uses a solid cavitiy of wax that liquifies as it warms up, moving the needle.


 
midnightmotors
Member since Aug-26-06
49 posts
Nov-07-06, 08:59 PM (EDT)
 
2. "RE: Electric Choke for scooter/moped carburettors How d"
In response to message #1
 
   Thats exactly how it works...
wax melts and moves the needle to where it needs to be...

but you cant just pull it out of the carb and turn the key on and see it move... the bike has to be running to generate the amount of heat needed to melt the wax...

these devices are not the most futurist/modern idea in the world, and its been my experience that they are not the most well made either...


 
Vespa Maineac
Member since Jan-31-04
212 posts
Nov-08-06, 02:29 PM (EDT)
 
3. "RE: Electric Choke for scooter/moped carburettors How d"
In response to message #2
 
   you should be able to hook the wire up to a 12vdc source (battery or charger) and watch for needle movement (or lack thereof)

From some source I can't remember:

(quote)
Aero 125, Elite 80/125/150/250, Helix bystarter (choke)
These models use an electric "choke". It's not a standard choke, in the sense that it doesn't choke off the flow of air (and make the fuel/air ratio richer). It is a device that shuts off the flow of air to the starting circuit as the scooter warms up. The bystarter is a small, black cylindrical device with two wires coming out of it. When the engine is running, 12V are applied to these wires. Over about 10 minutes or so, the bystarter warms up as the engine warms up. There is some wax in the bystarter (believe it or not) that is heated by a small heater. It expands, and extends the bystarter needle about 1/8". This is enough to close off the starting circuit.
After a number of years, the device builds up electrical resistance and it doesn't do its job any more. A new bystarter has a resistance of about 4 ohms. When resistance builds to over 10 ohms, it should be replaced.
To check for proper bystarter function, there is a complex test in the service manual that can be performed, but there is a simple test that works almost as well. Remove the bystarter and examine it. Are the wires in good shape? Is the needle in good shape? Nothing looks broken? Hook up a 12V source to the two wires. After about 10 minutes, the bystarter should become warm, and extend the needle 1/8" or so. Measure it with a pair of vernier calipers or whatever you have handy. If it extends properly it's probably ok. The only sure way to tell if it is bad is to do the full test as described in the service manual. This involves removing the carb and leaving the bystarter attached. Draw a vacuum in the starting circuit outlet. There should be little resistance when the bystarer is cold and plenty of resistance when the bystarter has been heated up. A bad bystarter will either not expand properly or not contract properly.
(end quote)


 
radlam
Member since Nov-6-06
8 posts
Nov-09-06, 01:37 PM (EDT)
 
4. "RE: Electric Choke for scooter/moped carburettors How d"
In response to message #3
 
   Thanks to you and the other gentlemen who offered their advice.

Yours was what I was really after, a thorough explanation rather than tantalising hints.
I think the Tempo choke must be shot in some way that renders it stuck out pernmanently as it is so difficult to start.

Its a pity it cannot be retro fitted with a simple manual choke as two strokes tend to warm up quickly much like my Atlantis 50 which can be ridden within 30 seconds of starting with a little choke applied when about to ride off.

This electric choke idea seems to be an answer looking for a problem to solve, as manual chokes do do the trick fine, its over complicated...

Thanks to you all again.

radlam


 
Vespa Maineac
Member since Jan-31-04
212 posts
Nov-09-06, 03:56 PM (EDT)
 
5. "RE: Electric Choke for scooter/moped carburettors How d"
In response to message #4
 
   From a GY6 performance site:
(quote)
Another way to get fuel enrichment on a stock carb with choke
removed is to add one of the plunger primers that are made for use on
snowmobile or ultralight engines. This primer plunger can be pumped and
squirt fuel into the intake and help with cold weather starting. A small 1/8"
fitting needs to be added where the fuel is squirted into the carburetor. Also,
a 1/8" hose needs to be added to supply fuel to the plunger primer. This
supply line can be T'ed off the main fuel line or fuel can be tapped off the
float bowl or however it works best on your application. Adding this plunger
primer is not the easiest method but it does work, and allows the stock carb
to be used in cold climates with auto choke eliminated. A more direct bolt in
carb like found on some of the Dazon buggy GY6 engine may be the easier
choice. Just check to make sure that it will fit your GY6 application. In any
case, whatever you end up doing, removing the stock automatic electric
choke can result in much more consistent performance. If your GY6 engines
runs consistently well all of the time, then don't worry about changing the
choke. However, if your GY6 engine runs strong one moment and then feel
sluggish the next, then it MIGHT be the auto choke sticking on. Just be
aware of this as a factor in performance.
(end quote)


 
radlam
Member since Nov-6-06
8 posts
Nov-10-06, 07:03 PM (EDT)
 
6. "RE: Electric Choke for scooter/moped carburettors How d"
In response to message #5
 
   Interesting idea, I may just cut off the top, drill a hole down through to the choke needle holder, remove the metering needle and attach a cable with a return spring.

A tug on the cable end, choke jet hole open...bike starts.

Let go cable, jet hole covered...choke closed, bike runs fine off throttle slide and main jet and idle when bike at rest.

Throw the electric bits as far away as I can. Along with the waxy goo etc

Problem solved...!!


 

 

 


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