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UTC

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Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: UTC
Posts: 2537
Location: Siam
 
Ossessionato
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: UTC
Posts: 2537
Location: Siam
UTC quote
I have some dumb questions.

Here is the first. On a Dellorto 16/16 carb does the higher the number on the main jet mean a bigger hole and a lower number means a smaller hole? Or is it the other way around where a bigger number means smaller hole and smaller number means a bigger hole😵‍💫?

I have a bone stock Vespa V9A1T with a Delorto 16/16 carb. I'm having trouble with my spark plug turning black. I've fiddled with the air screw and idle to no end with poor results.

The Scooter lounge website shows a stock V9A1T with a 16/16 carb should have 63 main jet. The new 16/16 Delorto carb I have bought from a German supplier has a 74 main jet which I believe is for a 125 Primavera. Could this be a problem? I also have a spare 70 main jet. It seems to run better on the 74 which has a smaller hole than the 70. All three numbers: 63, 70, 74 are confusing to me.

All the other jets match up with the recommended jets on Scooterlounge. It's just the main jet that I'm questioning.

Any recommendations are gladly accepted.

Note: It has all new stator coils, new properly gapped points, a new condensor, and is timed correctly.
@christopher_55934 avatar
UTC

Ossessionato
2007 Stella 225
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Posts: 3547
Location: Rochester, Minnesota
 
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@christopher_55934 avatar
2007 Stella 225
Joined: UTC
Posts: 3547
Location: Rochester, Minnesota
UTC quote
Smaller number smaller hole. How are you measuring hole size?

Maybe you have a few jets from different manufacturers with poor quality control?
@xantufrog avatar
UTC

Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
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Posts: 8892
Location: Atlanta, GA
 
Moderibbit
@xantufrog avatar
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: UTC
Posts: 8892
Location: Atlanta, GA
UTC quote
nomadinsiam wrote:
I have a bone stock Vespa V9A1T with a Delorto 16/16 carb. I'm having trouble with my spark plug turning black. ...

The Scooter lounge website shows a stock V9A1T with a 16/16 carb should have 63 main jet. The new 16/16 Delorto carb I have bought from a German supplier has a 74 main jet which I believe is for a 125 Primavera. Could this be a problem?
Yes. The carb is used on all sorts of bikes - the jet that comes in it should not be expected to be correct for yours. Put a 63 in and take her for a ride with a fresh plug.
OP
UTC

Ossessionato
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: UTC
Posts: 2537
Location: Siam
 
Ossessionato
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: UTC
Posts: 2537
Location: Siam
UTC quote
Christopher_55934 wrote:
Smaller number smaller hole. How are you measuring hole size?

Maybe you have a few jets from different manufacturers with poor quality control?
I'm just looking at the holes and see a difference.
I think there might be something going on where someone drilled the 70 out which makes it look bigger. The 74 is a new unmolested jet. The 70 is from an old carb.
⚠️ Last edited by nomadinsiam on UTC; edited 1 time
OP
UTC

Ossessionato
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: UTC
Posts: 2537
Location: Siam
 
Ossessionato
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: UTC
Posts: 2537
Location: Siam
UTC quote
xantufrog wrote:
Yes. The carb is used on all sorts of bikes - the jet that comes in it should not be expected to be correct for yours. Put a 63 in and take her for a ride with a fresh plug.
If I put a 63 or 65 in place of the existing 74 would that reduce the black sooty plug? I'm thinking of buying a 63, 65, and a 68 to try each until I get the right result.

For some reason, I have no problems dealing with carbs, jets, and plugs in large frames. It's this damn smallframe that has plagued me from day one with one weird thing or another.

Thanks for the replies gents.
@xantufrog avatar
UTC

Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: UTC
Posts: 8892
Location: Atlanta, GA
 
Moderibbit
@xantufrog avatar
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: UTC
Posts: 8892
Location: Atlanta, GA
UTC quote
Yes - your current jet is ~10 points too rich for your setup and will make the plug black and sooty. I also assume it is underwhelming to ride right now
@xantufrog avatar
UTC

Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: UTC
Posts: 8892
Location: Atlanta, GA
 
Moderibbit
@xantufrog avatar
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: UTC
Posts: 8892
Location: Atlanta, GA
UTC quote
P.s., I agree my et3 is way more finicky than my p200 to tune. Doesn't help that it's a bigger pain to get in there and work too.
OP
UTC

Ossessionato
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: UTC
Posts: 2537
Location: Siam
 
Ossessionato
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: UTC
Posts: 2537
Location: Siam
UTC quote
Yes, it's rather gutless, especially accelerating from a stop in first gear.

I am very used to the GS and SS where there isn't really a choice on jet sizes. I have now come to realize that small frame carbs have a wide range of jets.

Thank xantufrog.
@dirty30dillon avatar
UTC

Enthusiast
Yes
Joined: UTC
Posts: 90
Location: CT
 
Enthusiast
@dirty30dillon avatar
Yes
Joined: UTC
Posts: 90
Location: CT
UTC quote
As stated, replacement carbs are not intended to be direct bolt-ons as they are used across models.

I would try a 65 firsr, and see how it feels. The bike should definitely run poorly with the 74, so hopefully the mid-60's brings back your power.
OP
UTC

Ossessionato
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: UTC
Posts: 2537
Location: Siam
 
Ossessionato
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: UTC
Posts: 2537
Location: Siam
UTC quote
Dirty30Dillon wrote:
As stated, replacement carbs are not intended to be direct bolt-ons as they are used across models.

I would try a 65 firsr, and see how it feels. The bike should definitely run poorly with the 74, so hopefully the mid-60's brings back your power.
I was thinking to start with a 65 as well.
Thanks for your input.
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