OP
UTC

Molto Verboso
One or two fun scoots....nothing too precious
Joined: UTC
Posts: 1975
Location: UK (South East)
 
Molto Verboso
One or two fun scoots....nothing too precious
Joined: UTC
Posts: 1975
Location: UK (South East)
UTC quote
I have acquired a 28mm VHST and intend setting it up for a Polini 177 and Scorpion pipe. I just need to know a good starting point. The carb was previously on a motorbike with the following config:

Main jet: 168
Idle jet: u36
Choke jet: 80
Slide: 45
Atomiser: 268 HN
Needle: D53 (clip on second notch from top)
Needle valve seat: 300

I have only set up SI carbs before and have no clue what I need to put in there.

Any help most appreciated.
⬆️    About 7 months elapsed    ⬇️
OP
UTC

Molto Verboso
One or two fun scoots....nothing too precious
Joined: UTC
Posts: 1975
Location: UK (South East)
 
Molto Verboso
One or two fun scoots....nothing too precious
Joined: UTC
Posts: 1975
Location: UK (South East)
UTC quote
Bumping this for those interested in VHST carbs
Ok, so I'm pressing ahead with the carb swap. Gonna use it on my DR177 motor, which I can afford to mess with and mess up.

I discovered that the HH, HN and HE atomisers are designed for four strokes, so I bought a two stroke atomiser bush for £3.50. I also bought AQ262 and AQ264 atomisers. Knocking out the old bush and installing the new one was easier than expected once I had followed a tutorial PDF published on Dellorto's website.

I also read that the VHST takes a much bigger main jet than the equivalent PHBH carb. Example: PHBH with 115 main = VHST with 140. Not sure why. I have a range of 6mm mains from 130 - 142, so I'll start with a 140, as many 177cc scoots with PHBH seem to run 110 - 115 mains.

The MB Development website and an article on Scooterhelp about Dellorto flat slides talk about drilling out the hole near the float needle and increasing the size of the float needle seat (from 250 - 350) to eliminate a fuel starvation issue below 3/4 fuel level. However, I think this applies only to the high-end VHSA and not the VHST. My float needle seat is a 300, so bang in the middle. Let's see what it's like.

With new gaskets and 'o' rings, the carb is ready to fit. I am going to take a few millimetres off the back of the inlet port, to give me:

Inlet port starts to open at 115 degrees BTDC (currently 105)
Inlet port fully closed at 65 degrees ATDC (no changes to front of inlet)
Inlet duration will be 180 degrees

The crank is a Mazz race flowed by Worb5.

Exhaust duration currently 167 degrees, so I'm going to raise the port by 2-3mm, aiming for 175-180 duration.

Sound plausible?????
⚠️ Last edited by swa45 on UTC; edited 1 time
OP
UTC

Molto Verboso
One or two fun scoots....nothing too precious
Joined: UTC
Posts: 1975
Location: UK (South East)
 
Molto Verboso
One or two fun scoots....nothing too precious
Joined: UTC
Posts: 1975
Location: UK (South East)
UTC quote
VHST 28mm jetting
Starting point for ported DR177 + SIP Road 2.0 Sport

Atomiser: AQ264
Pilot/idle: S42
Main: 140
Choke: 60
Needle valve seat: 300
Slide: 45
Needle D53 (second notch from top)
@ginch avatar
UTC

Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
Joined: UTC
Posts: 8613
Location: Victoria, Australia
 
Veni, Vidi, Posti
@ginch avatar
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
Joined: UTC
Posts: 8613
Location: Victoria, Australia
UTC quote
Have you had a look at http://lfs.alexander-hepp.de/? Under DR 177 there are 3 VHSTs listed, it might help you a little. What bike did you get it from?
OP
UTC

Molto Verboso
One or two fun scoots....nothing too precious
Joined: UTC
Posts: 1975
Location: UK (South East)
 
Molto Verboso
One or two fun scoots....nothing too precious
Joined: UTC
Posts: 1975
Location: UK (South East)
UTC quote
carb was on a 2008 Aprilia RS125 with the full power spec
⬆️    About 9 years elapsed    ⬇️
UTC

Lurker
Sprint Veloce 76
Joined: UTC
Posts: 3
Location: London
 
Lurker
Sprint Veloce 76
Joined: UTC
Posts: 3
Location: London
UTC quote
swa45 wrote:
Starting point for ported DR177 + SIP Road 2.0 Sport

Atomiser: AQ264
Pilot/idle: S42
Main: 140
Choke: 60
Needle valve seat: 300
Slide: 45
Needle D53 (second notch from top)
UTC

Lurker
Sprint Veloce 76
Joined: UTC
Posts: 3
Location: London
 
Lurker
Sprint Veloce 76
Joined: UTC
Posts: 3
Location: London
UTC quote
How did you go with this setup in the end with these jetting numbers???

I'm in the same boat as trying to find the correct slide, atomiser and needle etc.
OP
UTC

Molto Verboso
One or two fun scoots....nothing too precious
Joined: UTC
Posts: 1975
Location: UK (South East)
 
Molto Verboso
One or two fun scoots....nothing too precious
Joined: UTC
Posts: 1975
Location: UK (South East)
UTC quote
ralus2006 wrote:
How did you go with this setup in the end with these jetting numbers???

I'm in the same boat as trying to find the correct slide, atomiser and needle etc.
Long time ago, but I eventually switched to a PHBH 28 and it was easy to configure. You can get VHSTs set up for Vespas and Lambrettas, but mine had some strange setup for a bike.
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