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@dcunited4life avatar
UTC

Molto Verboso
No moar Vespas...sold them all
Joined: UTC
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Location: Denver City Denver
 
Molto Verboso
@dcunited4life avatar
No moar Vespas...sold them all
Joined: UTC
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Location: Denver City Denver
UTC quote
Hello:

Here is my setup. Just looking for some insight on jetting and tuning as my bike is being a little difficult with me at the moment. Here's the specs:

1964 Vespa GL
166cc 2-port kit from scooterworks
20/20 carb-
55/160 idle jet
160
BE3
100 main
2 1/2 turns out on the mix screw
Idle screw is fully turned in
SIP road exhaust

It was running really good when I first got it together but as it has broken in and the weather has warmed up I've had to start tinkering with it to keep her going. She still causing me issues though so I am thinking MV insights might help.

1st issue- Low idle, I bumped the idle jet up from a 38/120 but I still have the idle screw in all the way....seems like it's almost there but not quite. Hesitant to bump up further because of issue number two I read about here.

2nd issue- Seems to lose power with throttle wide open from the middle to the top of the range. I read on here that too rich a mix will cause some sputtering. Plug chop looks fine and chocolaty but maybe the larger idle jet+same BE3+100 main is causing a rich mix at higher throttle ranges? Before tinkering with the idle mix screw, I would rev it up high during adjustment to ensure smooth operation across the range but on the upper end of the range it seems to start missing like there is a rev limiter or something. I read here that this too can be indicative of too rich a mix but it's doesn't seem like it's 4 stroking but more of a rev limiter sound.

Backfiring....used to start in 2-4 kicks...now it takes more and often it will backfire loudly then following that start up after the 1-2 more kicks. This seems to be a rule, backfire, then start right up. It never enjoys having the choke pulled out to start but does like the fuel on unless it's already warmed up then it prefers fuel off.

FYI points and ignition are NEW and bike has strong spark. Points are gapped to .330 mm, anything bigger and it won't start. It ran so well when I first got it together I didn't have to do much tinkering with the carb at all....now that it is broken in though and warming up outside it's being a bit troublesome. Also, I replaced the points due to the screw holding them slipping and closing the gap (talk about power loss) so I went ahead and replaced them while I was in there. Any thoughts on my jetting setup or perhaps should I be looking somewhere else? I didn't mention timing because I simply installed the stator the way I found it (I took pictures during dissassembly) and the motor was running when I bought it but needed to be rebuilt due to a bad selector rod bearing and rear wheel bearing. Thanks in advance everyone.
UTC

Veni, Vidi, Posti
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Location: Tega Cay, SC
 
Veni, Vidi, Posti
Joined: UTC
Posts: 7564
Location: Tega Cay, SC
UTC quote
What is your timing set at?
@socalguy avatar
UTC

bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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Location: So Cal
 
bodgemaster
@socalguy avatar
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
Joined: UTC
Posts: 7223
Location: So Cal
UTC quote
Not an expert in jetting by any stretch, I'd consider dropping down to a BE3. Your main/air combo seems about right, but if power is dropping off from mid- to WOT the BE4 may be introducing too rich a mixture from your main jet stack. A leaner atomizer will give you a smaller amount of mixture going to the venturi when you're on the throttle.

As for the idle, I'd try a 52/140, it's not that big a difference over what you have. But it should give you some adjustment in your idle speed and bring your choke back into play.
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UTC

Molto Verboso
No moar Vespas...sold them all
Joined: UTC
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Location: Denver City Denver
 
Molto Verboso
@dcunited4life avatar
No moar Vespas...sold them all
Joined: UTC
Posts: 1087
Location: Denver City Denver
UTC quote
SoCalGuy wrote:
Not an expert in jetting by any stretch, I'd consider dropping down to a BE3. Your main/air combo seems about right, but if power is dropping off from mid- to WOT the BE4 may be introducing too rich a mixture from your main jet stack. A leaner atomizer will give you a smaller amount of mixture going to the venturi when you're on the throttle.

As for the idle, I'd try a 52/140, it's not that big a difference over what you have. But it should give you some adjustment in your idle speed and bring your choke back into play.
It's already rocking a BE3...but I see what you are thinking...so perhaps a bit leaner then in the mixer tube and a richer idle. WOuld a leaner mixer tube require a larger main jet? I can always do a plug chop as well to figure it out but curious to know.
@shipscat avatar
UTC

Hooked
vespa 125 vnb1t
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Posts: 392
Location: antibes , france
 
Hooked
@shipscat avatar
vespa 125 vnb1t
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Location: antibes , france
UTC quote
try to isolate your problems 1 by 1 and not all at the same time you will go round in circles
first off check your wires on the stator for chaffing
when you changed the points did you change the condenser ?
they should be changed at the same time , a bad condenser causes backfiring
its important check the timing each time you tinker with points

as i understand the idle jet opperates to about 1/4 throttle , mid to 3/4 throttle the air corrector mixer tube comes in to play , full throttle main jet and the rest of the gang come into play too !!!
what happens when you screw the mixture screw all the way in ? dont take it as gospel that 2 1/2 turns is the be all and end all , experiment
its a bit of voodoo to get the correct jetting as each jet overlaps and influences the other
you can have 2 bikes the same but the best jetting for each may not the same

its like these vespas have personalities

like i said one step at a time and good luck
i'm still experimenting
@socalguy avatar
UTC

bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
Joined: UTC
Posts: 7223
Location: So Cal
 
bodgemaster
@socalguy avatar
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
Joined: UTC
Posts: 7223
Location: So Cal
UTC quote
dcunited4life wrote:
It's already rocking a BE3...but I see what you are thinking...so perhaps a bit leaner then in the mixer tube and a richer idle. WOuld a leaner mixer tube require a larger main jet? I can always do a plug chop as well to figure it out but curious to know.
Sorry for the typo, but you get the drift, consider an atomizer that will allow more air in the mix. If you're running a BE3 try whatever the next leaner one is - BE2? You want to let your carb breathe. I wouldn't increase the main until you see if the atomizer smooths things out. Like someone said, one step at a time. When your main is on you'll know it, you won't have to look at the plug.
@vyatka avatar
UTC

Molto Verboso
'61 GS150Cushman '63 GS160, '74 Primavera, '77 Rally 200,'80 P200E '05 PX150,'13 946,'64 Vyatka VP150,'77 Vyatka-Elektron,'07 GTS250, '63Tula200M
Joined: UTC
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Molto Verboso
@vyatka avatar
'61 GS150Cushman '63 GS160, '74 Primavera, '77 Rally 200,'80 P200E '05 PX150,'13 946,'64 Vyatka VP150,'77 Vyatka-Elektron,'07 GTS250, '63Tula200M
Joined: UTC
Posts: 1127
UTC quote
100 main with 166cc and Sip road sounds too small to me.
UTC

Hooked
Joined: UTC
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Location: Florida, USA
 
Hooked
Joined: UTC
Posts: 164
Location: Florida, USA
UTC quote
Start with the idle circuit first and don't move on to the main stack until you have a nice steady idle that responds to the mixture AND idle screw settings. Shipscat is right, you will get in a tizzy trying to adjust everything at once.
OP
@dcunited4life avatar
UTC

Molto Verboso
No moar Vespas...sold them all
Joined: UTC
Posts: 1087
Location: Denver City Denver
 
Molto Verboso
@dcunited4life avatar
No moar Vespas...sold them all
Joined: UTC
Posts: 1087
Location: Denver City Denver
UTC quote
vyatka wrote:
100 main with 166cc and Sip road sounds too small to me.
Agreed, but any larger and it gets oily. I was running a 98 in there for a bit actually and it was only starting to lean out the plug. That's why I am curious as to how the mix tube works in conjunction with the main. If I get it to idle well then maybe if I go down in the mix tube I'll need to bump up the main and get it closer to where it seems like it should be. Also remember, this is a 2-port 166cc kit and it's surprising to me how little fuel this thing goes through relative to 3 port P200's I have had and kitted bikes I've worked on for friends. (177cc Stella, a VBB with a third port cut in it and a stella stock top end). I'm gonna fiddle with the idle a bit more then move onto the main stack. Thanks for the insights.
OP
@dcunited4life avatar
UTC

Molto Verboso
No moar Vespas...sold them all
Joined: UTC
Posts: 1087
Location: Denver City Denver
 
Molto Verboso
@dcunited4life avatar
No moar Vespas...sold them all
Joined: UTC
Posts: 1087
Location: Denver City Denver
UTC quote
shipscat wrote:
try to isolate your problems 1 by 1 and not all at the same time you will go round in circles
first off check your wires on the stator for chaffing
when you changed the points did you change the condenser ?
they should be changed at the same time , a bad condenser causes backfiring
its important check the timing each time you tinker with points

as i understand the idle jet opperates to about 1/4 throttle , mid to 3/4 throttle the air corrector mixer tube comes in to play , full throttle main jet and the rest of the gang come into play too !!!
what happens when you screw the mixture screw all the way in ? dont take it as gospel that 2 1/2 turns is the be all and end all , experiment
its a bit of voodoo to get the correct jetting as each jet overlaps and influences the other
you can have 2 bikes the same but the best jetting for each may not the same

its like these vespas have personalities

like i said one step at a time and good luck
i'm still experimenting
Stator has been rewired y a Lambretta mechanic here in town when I did the rebuild on the motor so that's cool

No I didn't change the condenser...that may be a solid idea.

When the mix screw is all the way in it exacerbates the issue with the "rev limiter" feel at open throttle. I've pretty much been trying to get that dialed in first. For example, this winter when I got the bike back together (we've had a cold one here) it was at 1 1/2 turns out....it seems better now at 2 1/2 as the weather has warmed/top end has broken in

I couldn't have said it better....each Vespa I have owned has been like a different girlfriend....each with their own quirks and personalities. Right now this one and I are going through a rough patch but she's pretty to look at so I'm keeping her around unless she starts to get ornery. I think with a little love she'll be feeling secure and loved again.
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