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My first day I've had free to concentrate on getting my 125 Special running since buying it.

It's totally standard with an unknown history. It came from Vicenza from a private collection and only completed 400 miles since a total restoration.

Since buying it last week it's always been a bitch to start. I noticed that the choke wasn't really doing much and the fuel was smelling a bit rank

So I changed the choke and adjusted it so that when it's on the piston/barrel disappears through the carb hole in the mouth.

Replaced the gearbox oil and fuel with a mixture of 3%

Replaced the spark plug 0.6 gap.

It started first time revved nicely, ticked over ok once warm. Nice!!

Took it for a quick spin around the block, ran ok. But very slow.


Tried starting it ten mins later, no go with or without choke. Pulled the plug. It was fouled badly. Replaced it and tried starting it. Ran ok again turned the ignition one more click to check lights. died!

Couldn't start it again. Pulled plug, fouled!! Turned fuel off pump kickstart without plug then checked spark. Good spark. Put the plug in tried starting no go.

Nightmare!

Thought, right pull carb off and checj and clean.

Carb is SH1/20

Main jet 105
Pilot jet 45
Slide 5914 - 2
Atomiser 5899 - 5
Starter jet 50
Float bowl 5gms

I cleaned all the above which did have debris and old fuel gummyness on parts.

I then put it together set the slide so it was just closed full with the throttle shut.

Air mixture screw 3/4 out.
Put it together with a new plug, again bloody hard to start.

Checked flow of fuel tap it's not a quick flow but would certainly would fill a cup in about 20-30 seconds.

Anyone any ideas what could be wrong?

All I can think of is trying a fast flow tap or venturing into the points system which I haven't a clue with.



Any suggestions would be great.

Ta
Kris

have you checked the points what plug are you using?

also when you say slow what speed do you think?

Tried 3 different plugs. B6es, b7 and b8.

No, not checked the points and to be honest will need to read about what to do as I've never had a bike that runs on them.

Just seemed very sluggish, smoked a bit too.

if you've not ridden a std 125 lambretta before it may seem a bit slow

Just reading Stickys book and it says if the engine stalls if you put the lights on it could be demagnetised flywheel, failing coil or point problem!

I'm guessing it could be one of these problems.

missing lynx wrote:if you've not ridden a std 125 lambretta before it may seem a bit slow

I'm pretty sure it's that

One man's "total restoration" can, unfortunately, be another man's "shining paint job" and throw the rest together.

By the sounds of some of the issues you have had with this scoot (cables also), it sounds to me like you need to buy Sticky's book and give it a systematic and thorough going over.

Sorry to sound negative but if it was restored only 400 miles ago it shouldn't be giving you these issues if it was done right.

Any signs of an air leak from cylinder head, cylinder base, exhaust manifold? What does the slide look like? Is it very shiny? Are the points firing at the right place? The list could go on and on.

A standard 125 Special is pretty nippy around town. You should feel it rev crisply and respond to the throttle well. It'll run out of puff on a dual carriageway when you get near 50mph though.

It was restored 400 miles ago but unsure how long ago that was, it could have been 10 years ago.

I'm sure you are right. I will plod along with it like the last one

you said that you had an isue with the choke. I think I would be looking at that to make sure that the choke is seating completely when off. That could easily be the cause of both rich running , fouled plug and reluctant throttle response.

Try disconecting the choke cable when the engine is warmed up and see if there is any improvement.

When starting from cold don't be tempted to give it a little throttle .It should start on zero throttle and choke on. The throttle cable adjustment should be set so that there is a slight gap under the bottom of the slide with the throttle fully closed.

johnnyXS wrote:you said that you had an isue with the choke. I think I would be looking at that to make sure that the choke is seating completely when off. That could easily be the cause of both rich running , fouled plug and reluctant throttle response.

Try disconecting the choke cable when the engine is warmed up and see if there is any improvement.

When starting from cold don't be tempted to give it a little throttle .It should start on zero throttle and choke on

Johnny, good point thanks will try slackening It off a touch.

Just slackened off the choke and it kicked first time no tick over but I can sort that in the morning.


Hopefully that's it Johnny, many thanks will have another fee hours on it tomorrow getting it prepped for the mot.

good luck with the test ..let us know how you get on.

Well it started on the fourth kick but just doesn't sound right.

I think it might be slide height and mixture screw so will play around with them a bit.


Lambretta club suggest 98 main jet and 1/2 turn out on the mixture screw.

I'm running 105 main jet any ideas if the mixture screw should altered?

Ta
Kris

According to the carb & jetting table on the Cambridge lambretta website your scoot should have a 5899-1 Atomiser not a 5899-5 The 5899-5 Atomiser has a considerably larger bore diameter and will flow a lot more fuel and air than the 5899-4 which should be fitted.

The main jet for your scoot should be a 99 (0.99mm) not a 105 ! it looks like the previous owner has tried to gain some more power by increasing the fuel delivery rate which may work at higher revs and cruising speeds but will play havoc with your starting , idle and initial throttle response.


Unless your engine has been tuned I would suggest that you obtain and fit the correct atomiser and a selection of main jets to tune with . you can buy a box of 12x mixed 5mm jets for about £12 if ou shop around the net. If you can't find an atomiser at a reasonable price I've probably got one you can have



Its essential that you make sure you have no air leaks around the inlet manifold to engine joint and to the carb otherwise any tning will be a complete waste of time . We'll assume that there are no leaks .
In your case I would start by making sure that the choke cable has a little free movement at the cable adjuster on the carb, when turned to the off position. Most new choke cable inners are too short by a few mm and consequently hold the choke valve slightly off the seat all the time giving an overly rich mixture. If there is insufficient adjustment to achieve this you may have to file or saw a smidgin off the choke cable bend .

You need to set your slide height first by adjusting your throttle cable adjuster on top of the carb until you have a reasonable tickover . Don't try get it too low at first .
When the engine has warmed up properly adjust the air screw. Start with the air screw about 1/2 a turn out and adjust it a quarter turn at a time. Give the throttle a blip and then wait at least 15 seconds or so for the setting to have an effect on the tick over and initial throttle response.

Basically if your mixture at idle is too rich the engine will sound lumpy and spluttery threatening to stall maybe.You'll need to screw the idle screw IN to weaken the mixture.
If the engine speed seems to vary up and down a little by itself then its likely to be too weak at idle in which case adjust the air screw out a quarter of a turn at a time to richen the mixture .
Don't set your tickover speed too high or the engine will start to use the main jet and distort your idle speed adjustments.

If you cannot achieve a steady idle speed by using the air screw adjustment between 1/2 turn and 2x turns out then you will probably need to change your pilot jet and possibly the atomiser for the correct one

if the engine is still unresponsive then you'll need to check that your timing is set correctly and the points gap is correct if you're using points that is

Cheers Johnny


I think I'm going to start at the beginning and strip the carb, exhaust and manifolds off and make sure they are air tight. Ive noticed a lot of oily residue underneath the manifold which is pretty rusty.

Then work through to the carb with the correct settings.

Once all that is done at least I know it's right and done properly.

Then if there is still problems I think I will bin the points and go electronic.

Cheers
Kris

that a good plan Kris. At least you will know that everything has been checked cleaned and adjusted and be familiar with everything when done..
Keep us in touch with progress as it may help others that arrive at this thread in the future with similar problems
johnny

Yes will do.

Thanks for your advice. Will keep you posted just writing a shopping list. Again!!

I don't want to contradict anyone but some 125 specials were fitted with a 105 or 107 main jet and a 5899-5 atomiser as you state