Carb settings for Mugello 186

[Revvers]

Hello all. Please bear with me as I don’t really know what I’m talking about. Having started using my Lambretta for work commuting instead of bimbling around, the fuel consumption appears to be poor. I’m doing 50 miles on 8 litres (25 to the gallon??)
My plug is black but dry, so assume it’s running too rich. The other day I had to stop at a level crossing and as I went to pull away, she completely bogged down.
She starts first or second kick.
At the mo, I have an X2 needle with a 40 slide. The little ring is on the top notch
Main jet-107
Float needle 200
Pilot 55
Starter (choke jet?) 70
Atomiser AV266
Looking at the Cam Lam site, should I change the atomiser to an AS?
Should I fit a 45 slide
Should the choke be a 55?
Would adjusting the mixture screw solve this? It is wound out about 1 1/2 turns
Mugello 186
28 PHBH No air filter, using the chiselspeed green thingy
5 speed gearbox
Was running a Scootopia clubman (am now running a Sip silent, but the issue was already there)
Any advice please?

[Storkfoot]

How did you arrive at the jetting you have now? Have you marked the throttle twist grip 1/8, 1/4, 1/2, 3/4 and wide open throttle and then tried to identify whereabouts on the throttle progression it bogs down? If not, I’d recommend you do. Sometimes just revving a warmed up engine on the stand will point you in the right direction. So, for
example, if you get a bogging down feeling at quarter throttle, with loads of smoke coming out of the exhaust, you may look at the slide -needle- atomiser.

I can’t advise you on the jetting for a Mugello, I am afraid. But, I’d be tempted to try a couple of things first:

Take off the filter. I tried one of that type of filters once but it tended to compress against the panel and make it very hard for the carb to breath. This made it too rich. Run the scooter around a bit and see what it is like without the filter. If it bogs down, check where on the throttle progression that is. That’ll give you an idea what you may need to changes you may need to make jetting wise.

Sometimes, it is easy to think that bogging down is as a result of a rich mixture but it can also be as a result of it being too lean somewhere on the throttle progression. Whilst your pilot of 55 is “probably” as big as you would want to go, having the needle on the top clip is quite lean. Try it on the second clip.

You say the scooter starts easily. Does it tickover without having to blip the throttle?

AS atomisers are not usually used on Lambrettas. They are generally leaner than AV atomisers and used more on motorbikes. Proceed with caution if you do try an AS.

A 45 slide is leaner than a 40. Leaning out the slide will have a marked effect on the rest of your jetting. I wouldn’t go down that route just yet. Slides are expensive and you may be better spending your money on a dyno session first.

Do you have an X7 needle to try?

[Revvers]

Hi Storkfoot, thank you for the reply. I don’t have an X7, but will get one to try. I was more concerned with the fuel consumption to be honest, and because of the plug being black, I presumed the fuelling was too rich and consequently the excess consumption (?)
I’ll remove the filter and take the ring down one on the needle and see how I get on.
The carb has been set at this for a while but I’ve not realised how bad the fuel consumption was.
I’ll give your suggestions a go and see how I get on. Thanks once again

[Storkfoot]

Remove the filter first and then, later on, see what the effect of raising the needle is. Removing the filter is going to instantly lean out all the jetting so do not go screaming down the bypass at 60 whilst you are sussing out whether the filter is your only issue.

From your description, I am more concerned by the bogging than the fuel consumption. Bogging shouldn’t happen if the air/fuel ratio is more or less correct. I am presuming that you have a very smokey exhaust plume. Is that right?

Have you had the top end off in the recent past?

[Revvers]

No major mechanicals for ages. I’m going to remove the filter and give it a try. The bogging down was an isolated incident which happened while I was sitting ticking over for over 5 minutes at a level crossing. I’ve also slightly lowered the choke slide as I’m not sure it was closing off properly.

[Warkton Tornado No.1]

Dell'Orto manufracture excellent components to enable good calibration to be achieved.

(IMHO the round slide carburetor is best left for four stroke engines they were designed for, but Dell'Orto have done an excellent job in allowing/marketing the PH series to be useable with a two stroke engine. Any know!edge/experience I have personally has been the result of setting up engines already fitted with Dell'Orto's of all varieties, including conversion of VHB's to operate with PH atomisers, needles & - in particular - the needle shroud)

Despite any apparent cynicism, in the interests of attempting to help, I would make the following observations in addition to the excellent advice already received.

The Post Originator is prepared to spend money in an attempt to make for a better running engine. That's good, but prior to shelling out for a new s!ide, consideration should be given to.modifying the 40 s!ide to a (more likely suitable) 45. This is easily accomplished with hand files & the knowledge of the difference between a 40 & a 50 etc. I can't say for.certain if it is actually a millimetre without checking, but whatever the amount, it can very easily be seen that a, say, '42-1/2' etc s!ide can be fashioned. Perhaps some kind reader with more than one slide size would confirm the variation?

What I would advocate is the procurement of a smaller atomiser to enable more accurate fuel control. It appears to be very popular to have greater size atomisers than those necessary fitted in Lambretta engines.....If in doubt, remove the main jet completely & try revving the engine out - most likely a lot of engines will run happily on a 262.....Hopefully the OP has a mate with a choice of atomiser......

Finally, as a matter of precaution, a larger float valve would be sensible. No need to go mad, but a safety factor that a valve greater than 200 provides is worth the expense, bearing in mind that once we get this puppy jogging along a bit more like intended, it can be a factor often overlooked.

Generally, a pilot of around 50 is a good starting.

By the way, had anybody noticed, I'm back.....

[Rich Oswald]

Welcome back WT1.

Just a few observations from my experience.

It should jet up fine with the green Chiselspeed panel filter. Martin Cook at Chis' sorted mine when it was boggy even without a filter at all.

I personally think a 55 pilot is way too big. People seem obsessed with 55 pilots for some reason. I think a 50 should be plenty.

As Storkfoot said, try an X7 needle on 2nd clip down with AV 266 atomiser, not AS.

I think your main jet may be a touch low.

Up your float valve to 300. Most tuners recommend at least a 300.

A 45 slide will lean the low down section and make it less boggy but do that last.

Hope this helps a bit.

Rich'