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1978 P125x
Malossi 166 kit
Spaco 20/20

I want to run this thing to the point where I foul plugs, then I can know when to start dialing the mixture back.

Am a bit confused on the rear screw. I have seen 3 or 1.5 turns out, but what does what? Is turning in the screw giving me a richer or leaner mix?

Also I have a choice between BE3 BE4, and BE5 middle, a 150 or a 160 top, and a 100, 102, and something else a bit bigger - but can't determine - on the bottom.

Seems to want to seize on me at higher speeds, and the plug is a nice chocolate brown, yet dry. Premix 2%

Any help wouldbe greatly appreciated....
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the main stack on yours should be bigger than stock

http://www.scooterhelp.com/tuning/vespa.malossi.166.html

start there

for the mix screw on the back of carb-start about 2 turns out
-start bike
-turn the idle screw(top of carb)right until it wont turn(gentle)
the bike should be idleing high
-then go back to mix screw and turn 'in' small amounts(leaning the mix)until the bike sounds like a screamer
-then turn 'out'(richening the mix)until it is a little rough
-find a happy medium
-this is only the mix for your 1st stage of carb
after the throttle is turned more than a third you are now into your stack
150/be3/115 or whatever

if any of this advise is wrong-please clarify
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I highly recommend signing up over at Stella Speed forum - those guys go into great technical detail on jetting a/f mix etc.

As for the a/f (rear) screw - the Spaco have a different thread pitch to the Dellorto, so for a delly, 1.5 turns is the starting point, but the higher pitched spaco is 3 turns

There's a great write up on Stella Speed about air correctors - http://forums.stellaspeed.com/viewtopic.php?f=15&t=12769&p=134160&hilit=be3+be4+be5#p134160
Quote:
One more word regarding mixers

A:

The more/bigger holes they have in the upper sections closer to the injector the later they start delivering fuel thru the injector.
As an example, the BE2 mixer has 4 rows with 4 big holes on each. The higher line of holes lies just in front of the inside end of the injector. This makes that the initilal flow demanded via the injector is satisfied with a leaner gasification because it will be just air form the air corrector passing thru the upper 4 holes of the BE2 mixer right thru the injector to the carb throat.

See it?

So, when is that the BE2 starts to deliver more fuel?

As the engine suction and more throttle opening create more vaccum on the injector area, it increases the total gas flow that passes thru it. At some point , the injector demands more flow than what can pass thru the A/C, and it creates a vaccum situation inside the main stack cavity. At that point this depression is equalized and the air comming from the A/C now passes thru ALL the 16 holes of the be2 mixer.There, the air flow picks up more fuel that lays closser to the bottom holes of the mixer.
In the main stack cavity the gas level lays under the below the lower holes of the mixer, arround the "BE?" mark of the mixer. Note that the bottom of the mixer is closed and it does not connect internally with the main jet. The fuel from the main jet lays OUTSIDE the mixer tube so that the air current entering via the A/C and comming thru the inside of the mixer tube atomizes, picks up the gas and takes it to the carb. venturi via the injector.

B.
The lesser/smallest holes they have in the upper sections closer to the injector the sooner they start delivering fuel thru the injector.
For instance a the 3rd (top) row of holes of a BE5 are smaller in size than those of the BE3. Hence, the air from the AC will start to pass thru the inferior holes of the mixer sooner on the BE5 and the fuel supply thru the main stack will kick in earlier.

The quickest in fuel response is then the BE4 since it is the only one who has only two row of holes at the bottom, closest to the fuel level. The BE4 will immediatelly respond to the injector vaccum and deliver a richer fuel atomization .


According to this theory, this is the order of the mixers, (from 1st to last to kick in)
BE4, BE5, BE3, BE1, and BE2
I found a nice little line drawing the other day of the dellorto/spaco carb and how it works, jets/mixer wise - it's bookmarked on my home pc, I'll post a link later
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Thanks!
To the both of you. That helps greatly (at least I am less confused now...)
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Molto Verboso
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I have a 20/20 carb, sito plus, malossi 166(160 be3 103)
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the 103 seems small

but i think you would know music

you have been one of the more knowledgable ones
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Music wrote:
I have a 20/20 carb, sito plus, malossi 166(160 be3 103)
I have those components, and I will try that combination. what plug are you using with the Malossi? I have the same as stock in mine, a B7HS, and worried that the plug doesn't seem to reach as far into the Malossi head as it did the stock head....

I know I'm asking a lot of this bike anyway, what with the sidecar and my fat ass (260#), but all I really want is reliable 40-45mph without seizing. My cylinder looks okay after having seized twice, with no scoring or mis-shaping going on. It just boggles me as to why this engine keeps wanting to seize when the stock components did just fine at 40mph, albeit really really lacking on uphills....
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I spent a lot of time looking at the charts on
the Stellspeed Forum
http://www.mintwood.net/stellastats/profiles.php?sb=4
as well as experimenting with different size jets.

I'm running a NGK B9HS plug

Jetting is sometimes a art form(and some luck) 8)

After much trial and error, my scooter is
in a very "sweet" spot. I have a lot power
through all gears, and it hit's 65 mph without a
problem(and it eats hills alive).
I ride on the highway with it(when I need to), and have done many
200 plus mile rides with it(almost every weekend).

Make sure to pull your plug often and see
what color it is.

RE: "worried that the plug doesn't seem to reach as far into the Malossi head"
I called Malossi USA directly, and they want you to use the shorter plug.
I've also confirmed this with many scooter mechanics.



Rob
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Whoa
You're running a much colder plug. Could that be the problem?
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Molto Verboso
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Quote:
I know I'm asking a lot of this bike anyway, what with the sidecar and my fat ass (260#),

You're running a much colder plug. Could that be the problem?
It works for my setup, but I don't have a side car on my scooter,
and I don't know how you have the rest of your
engine set up, including the air filter.

Try a few different combinations, always err on the cooler side,
I would rather foul a plug than seize an engine.


Plus remember all scooters are different, you can only use
what someone else does as a guide.






Rob
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Read this shit, yo:

http://www.strappe.com/plugs.html

Much better tuning than simply looking at the end of the plug.
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Hooked
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For the non-technically minded - this is how your carb works and how various parts interact

External inline image provided by member with no explanatory text

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