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@psma avatar
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Hooked
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
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Hooked
@psma avatar
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
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Posts: 277
Location: Madeira Island
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Hi, is a Dellorto SHB 16/16 enough for a small frame with Polini 75 cylinder, Vespatronic, Polini banana exhaust and a Polini extended intake crankshaft?
Thanks
OP
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125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
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Hooked
@psma avatar
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
Joined: UTC
Posts: 277
Location: Madeira Island
UTC quote
I explain a bit the question above:

My small frame had all the symptoms of an air leak, but where? I didn't look close enough, so was advised to get a reed valve intake manifold, maybe the rotary valve was damaged? Nop, when the intake manifold arrived I realized the air leak was after the carb, size didn't match the manifold and *someone* tried to close the gap with a rubber band … Facepalm emoticon

As I already had the new manifold, whatever, I installed it anyway

I think carb was around 19,5 and manifold 20,5mm ? Can't say for sure. So I dremmel out the excess until it fitted. Engine is ok now, But the question arises, different sizes why? Carb should obviously be bigger or the manifold smaller.
@scootermarc69 avatar
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UTC quote
The reed intakes for SHB carb are made to fit the specific size carb, the difference being only at the piece that the carb connect to.
did you order the 16/16 version? If you haven't completely removed the rotary pad I would expect poor results.
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OP
@psma avatar
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Hooked
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
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Posts: 277
Location: Madeira Island
 
Hooked
@psma avatar
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
Joined: UTC
Posts: 277
Location: Madeira Island
UTC quote
scootermarc69 wrote:
The reed intakes for SHB carb are made to fit the specific size carb, the difference being only at the piece that the carb connect to.
did you order the 16/16 version? If you haven't completely removed the rotary pad I would expect poor results.
Yeah, the one in the right. Question is the original manifold (only a tube) didn't fit already. Could that be a defective carb? the thickness of the aluminium wasn't even all around, it was a bit ovalized. I had to take around 1mm off and it fitted fine. I noticed a slight increase in torque after the reed valve intake.

Anyway, considering the size, is a 16 ok for this engine?
OP
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Hooked
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
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Posts: 277
Location: Madeira Island
 
Hooked
@psma avatar
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
Joined: UTC
Posts: 277
Location: Madeira Island
UTC quote
This was ovalized, those sections were not the same thickness. I wasn't remembering this on #2 above. And it was untouched so my guess some defective part? The previous owner went the easy way, but he really almost didn't run the Vespa after the rebuild.

He regrets having sold it, his wife didn't want to, in this case 1/WAF
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@dirty30dillon avatar
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UTC quote
Sounds like the previous owner tried to over tighten the carb onto the misfitting intake and ovalized it.

It's not a defective carb it was mis-installed. And dremelling that sealing surface is a sure way to have another airleak.
OP
@psma avatar
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Hooked
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
Joined: UTC
Posts: 277
Location: Madeira Island
 
Hooked
@psma avatar
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
Joined: UTC
Posts: 277
Location: Madeira Island
UTC quote
Dirty30Dillon wrote:
Sounds like the previous owner tried to over tighten the carb onto the misfitting intake and ovalized it.

It's not a defective carb it was mis-installed. And dremelling that sealing surface is a sure way to have another airleak.
No. Impossible to ovalize that with force, it simply didn't enter the manifold, it was very visible without measuring. They just put the tube one close to the other and then with rubber like bicycles inner tubes wrapped around and fixed with clamps. The dremmel was done with care in small steps until matching, the vespa returned to perfect idle after that
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