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@rogscoot avatar
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Vespa PX200/Bajaj Chetak/GS150 VS5/Piaggio Cosa/Lambretta Lynx
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@rogscoot avatar
Vespa PX200/Bajaj Chetak/GS150 VS5/Piaggio Cosa/Lambretta Lynx
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Location: Berkshire - UK
UTC quote
Hi there,

I'm setting up a PX125 engine with Pinasco 3-port cast iron barrel (standard crank) SIP road exhaust and 24/24E carb.

The main jet sizes I've seen used for this config seem to be around 118-122 range but this for this engine these sizes were way too rich and it just bogged like crazy.

I'm down to a 105 main now which is better but still a little boggy but I wanted to check to see if anyone had a main smaller than that with this setup?

I was going to also check/swap the CDI because I've had these fail in the past which give hesitancy/bogging symptoms.

Cheers!
@sdjohn avatar
UTC

Johnny Two Tone
'15 GTS300, '86 PX125EFL, '66 VBB, '01 ET4
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Posts: 8539
Location: San Diego, CA
 
Johnny Two Tone
@sdjohn avatar
'15 GTS300, '86 PX125EFL, '66 VBB, '01 ET4
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Posts: 8539
Location: San Diego, CA
UTC quote
Are you at altitude?

If not, check your plug, that is very small for a main on this kit.
@mjrally avatar
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Veni, Vidi, Posti
73 & 74 Rally, 76 ET3, 80 P200, 06 PX150, 59 Ser 2, 65 Silver Special, 90 V5N 50, 2015 HD Road Glide Special
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Location: Oceanside, CA
 
Veni, Vidi, Posti
@mjrally avatar
73 & 74 Rally, 76 ET3, 80 P200, 06 PX150, 59 Ser 2, 65 Silver Special, 90 V5N 50, 2015 HD Road Glide Special
Joined: UTC
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Location: Oceanside, CA
UTC quote
I just looked in my notes and a friends exact setup was a 160, BE4, 118 main stack. Granted thats for sunny Southern California right at sea level. You might be able to go smaller since youre not dealing with warmer temps.

If youre still bogging, have you verified the choke circuit is closing? Swap carbs and see if that changes things. If not, swap electrical components.
OP
@rogscoot avatar
UTC

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Vespa PX200/Bajaj Chetak/GS150 VS5/Piaggio Cosa/Lambretta Lynx
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@rogscoot avatar
Vespa PX200/Bajaj Chetak/GS150 VS5/Piaggio Cosa/Lambretta Lynx
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Location: Berkshire - UK
UTC quote
I'm not at altitude, and seeing another 118 main I think I'm going to try the electrical route.

I'll swap the CDI over with a known good one for starters and see how that goes!

Cheers!
@sdjohn avatar
UTC

Johnny Two Tone
'15 GTS300, '86 PX125EFL, '66 VBB, '01 ET4
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Posts: 8539
Location: San Diego, CA
 
Johnny Two Tone
@sdjohn avatar
'15 GTS300, '86 PX125EFL, '66 VBB, '01 ET4
Joined: UTC
Posts: 8539
Location: San Diego, CA
UTC quote
It's always funny when you go from the mobile back to the web version of this page, now I see you are in the UK - not many mountains there . On the mobile those details are missing.
@kowalski avatar
UTC

Addicted
2005 Stellalossi 177 Fe
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Posts: 518
Location: MA
 
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@kowalski avatar
2005 Stellalossi 177 Fe
Joined: UTC
Posts: 518
Location: MA
UTC quote
A 105 main jet actually is not so crazy if you have rotary valve induction and haven't modified the crank. Nonetheless, you can't just look at the main jet in isolation. I'm guessing the standard air corrector tube/mixer tube combo for this engine would be AC140/BE5. Can you confirm that is what you you are working with?
OP
@rogscoot avatar
UTC

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Vespa PX200/Bajaj Chetak/GS150 VS5/Piaggio Cosa/Lambretta Lynx
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@rogscoot avatar
Vespa PX200/Bajaj Chetak/GS150 VS5/Piaggio Cosa/Lambretta Lynx
Joined: UTC
Posts: 310
Location: Berkshire - UK
UTC quote
I have a new SPACO non-autolube PX200 24/24E carb and it's using the BE3/160 config.
This morning I swapped the CDI over to a known good one but same result so I think it's still likely to be carb.

I tried a 116 main again just to see and it's definitely too large to be able to rev-out at full throttle.

The 105 jet allows me to rev-out at full throttle but still hesitant/4-strokey at 1/3 throttle.

Ticks over and pulls away fine so I think the pilot is ok.

I actually went down to a 98 main jet just to try while on it's centre stand in the garage and that was definitely too small because when revving it has a big pause before it revs and clearly sounds too lean.

Cheers!
OP
@rogscoot avatar
UTC

Hooked
Vespa PX200/Bajaj Chetak/GS150 VS5/Piaggio Cosa/Lambretta Lynx
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Location: Berkshire - UK
 
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@rogscoot avatar
Vespa PX200/Bajaj Chetak/GS150 VS5/Piaggio Cosa/Lambretta Lynx
Joined: UTC
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Location: Berkshire - UK
UTC quote
sdjohn wrote:
It's always funny when you go from the mobile back to the web version of this page, now I see you are in the UK - not many mountains there . On the mobile those details are missing.
We just have grassy rolling hills where I live!
@robbie_11 avatar
UTC

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PX
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Location: Switzerland
 
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@robbie_11 avatar
PX
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Location: Switzerland
UTC quote
I would start at 122 and see how the plug looks and go from there. I think on my Pinasco 177 I have a 118 but its the Alu cylinder.
@kowalski avatar
UTC

Addicted
2005 Stellalossi 177 Fe
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Posts: 518
Location: MA
 
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@kowalski avatar
2005 Stellalossi 177 Fe
Joined: UTC
Posts: 518
Location: MA
UTC quote
I think your mid-throttle bog is a lean bog and the main cause is the BE3 mixer tube, which tends to be too lean for these small block 177 kits. You probably will need a BE5 and possibly a BE4. The BE5 typically is paired with a 140 air corrector so I would try that combo first. Once you get the mid-throttle performance sorted, it should be fairly easy to figure out the right main jet.
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