Engine bogs down and stalls... SOS...

[Scouse Scooterboy]

Got a 1960 Li150 Series 2 fitted with a BGM RT195 kit, BGM electronic ignition, BGM Clubman, 28 PHBH Dellorto with air filter.

A few times now when changing down the gears for a roundabout, but more often when pulling away in 1st, the engine bogs right down and stalls on me. The last time the scoot started 1st kick (yes really!), and 2 up it pulled great through the gears for a couple of miles. At a 2nd set of lights, letting out the clutch and easing the throttle back it bogged down / 'blugggrrrhhh' noise / stalled. Managed to just get it started but really struggling to tick over and didn't respond to any throttle. So the walk of shame pushing it home.

No idea what's causing the problem (and have had a good Lammy man check it out). Carb been off 3 times now and cleaned, removed the inline fuel filter too. Checked the petrol tap breather is ok and not blocked. Really frustrating as sometimes the scoot starts and runs bloody great. Out on it last week for a 30 mile ride and it didn't skip a beat. Really need help with this one. Anyone experienced the same / similar before and point me in the direction of what's causing this and a fix?

[HxPaul]

Sounds electrical.Try swapping the CDI unit.

[Tractorman]

I had this problem with a mugelo 225 kit that only started when I fitted a BGM exhaust so after a while of the same problem as you I took it off and put the 42mm exhaust back on and it cured it. My only idea is there was not enough back pressure with the BGM but someone who knows more about tuned engines could well disagree.

[Scouse Scooterboy]

Thanks HxPaul and Tractorman. 2 things for me to look into...

[CHRIS in MARGATE]

To me it sounds very familiar and I think it will run clean with the air filter off and the jetting raised a little.

[Storkfoot]

What type of air filter do you have? Did it run well until recently? Does it start better cold than warm? When it happens have you tried taking the air filter off?

[MickYork]

Stator ?

[Scouse Scooterboy]

What type of air filter do you have? Did it run well until recently? Does it start better cold than warm? When it happens have you tried taking the air filter off?

The air filter is the like this which I got from MB... http://www.lambrettaspares.com/spares/125*190-cc-engines/lambretta-carburettor-kit,-30mm-dellorto-phbh,-small-block,-filtered/mbd30k3.html

It usually starts fine from cold or warm. When its happened in the past I've left it overnight and it usually starts again ok the next day. Will take it off and try a few runs on it...

[Scouse Scooterboy]

Stator ?

Would be a problem all the time and not just now and again if the stator was knackered?

[Scouse Scooterboy]

To me it sounds very familiar and I think it will run clean with the air filter off and the jetting raised a little.

Going to take air filter off and try a few close to home runs over the next week...

[MickYork]

just had another thought

Could the choke be sticking (sometimes) ? either the cable, the plunger......... or the little rubber seal leaking

[Storkfoot]

There are lots of possible reasons, many of which have been referred to here. I could add port timing and ignition timing too but, if it was me, I'd start with the air filter and elbow. Often, if you're running rich somewhere on the throttle progression, or if the port timing is out, you can get the filter and elbow full of over rich mix which makes it bog down.

As you know, I am sure, if you take the filter off, don't go and hold it wide open throttle on the dual carriageway. If it does bog down when you're out on a run, stop, try and rev it with the filter still on, on the stand. Then take the filter off (look for signs of petrol/ oil, rich vapour in the elbow) and rev it on the stand.

It may be an idea to post your carb settings too.

[MickYork]

Stator ?

Would be a problem all the time and not just now and again if the stator was knackered?

You can get intermittent faults on the stator as it gets warm and expands/contracts.

[citydaz]

I had a very similar problem.
turned out there was a bare wire in the heatset and the electricity was escaping all over the place.
after this the scoot was much better but would be a bit boggy at low revs.
so I fitted a larger ram air filter and this seems to have cured it

[Adam_Winstone]

Failing stator, incorrect jetting + filter combo, leaking float in carb (check it for signs of petrol on the inside?

[Scouse Scooterboy]

There are lots of possible reasons, many of which have been referred to here. I could add port timing and ignition timing too but, if it was me, I'd start with the air filter and elbow. Often, if you're running rich somewhere on the throttle progression, or if the port timing is out, you can get the filter and elbow full of over rich mix which makes it bog down.

As you know, I am sure, if you take the filter off, don't go and hold it wide open throttle on the dual carriageway. If it does bog down when you're out on a run, stop, try and rev it with the filter still on, on the stand. Then take the filter off (look for signs of petrol/ oil, rich vapour in the elbow) and rev it on the stand.

It may be an idea to post your carb settings too.

Thanks. When it happens and I try to kick it over, it barely ticks over and then stalls. If I try and give it any throttle, nothing happens / no response.

My carb is
Choke jet - 70
Idle jet - 55
Slide - 40
Needle - X7
Needle jet - AV264
Main jet - 120
Clip 2nd from top

[Storkfoot]

Slightly unusual to see an AV264 with an x7. Did you set up the carb?

[johnnyXS]

if it starts and runs fine some of the time then I would think that there is not likely to be anything wrong with your carb .
(I presume that you have already checked your fuel flow and tank vent?)

From your description my inclination would be to check the electrics particularly the stator ,wires from the stator, coil etc for a short.

[Scouse Scooterboy]

if it starts and runs fine some of the time then I would think that there is not likely to be anything wrong with your carb .
(I presume that you have already checked your fuel flow and tank vent?)

From your description my inclination would be to check the electrics particularly the stator ,wires from the stator, coil etc for a short.

Hi JohnnyXS

Thanks. After speaking to a few people last night, the electrics seems the most likely culprit. Will check it over at the weekend...

[johnnyXS]

good luck matey..
don't want to miss all this good weather