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Hey everyone its been actually some years since I last posted anything on this forum, I hope everyone is okay and well

Since my last postings on this forum I have been building an SS90 Replica which has been fun and scary at the same time, I have always hated the idea of cutting any vehicle frame let alone a classic Vespa,

I know some of you will say I am stupid for cutting but its done now so no going back

The motor I do however need some tech advice on please I have used the best Independent Vespa Mech in South Africa for tuned motors but he is still having a small issue maybe someone can assist with in terms of a flat spot in the Rev range and a spike in CHT in this flat spot at higher Revs (Tony will respond and explain more for me please can someone give us some advice)

motor build as follows,

Racing Crankshaft Mazzucchlli Race
PHBL25B Malossi reed valve kit
DRT Sport Clutch 393.211
DRT Sport Gearbox 29/68 (2.34)
SIP VAPE Sport Ignition
VSP Road race exhaust
Racing Polini Cylinder GS 130cc by Worb5

the bike feels very strong for the small cc. but cant really tell as I have not yet really ridden very hard.

I know there are a few small things that are not perfect and they already bother me on the frame build BUT in my opinion I am happy with the overall outcome of this build.
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Sergeant at Arms
Weird 80's Vespas & Cool Vintage Lambrettas
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while you didn't say what your port timings were, or the inlet timing is, or if it's barrel or case inducted the thing that sticks out to me immediately is that seems like an awfully small carb for such a racy pipe.

I'd be looking there and at my port timing to make sure it's complimentary to the pipe.
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Thank you for the very prompt response, to be totally honest I dont know the timings Tony will have to respond to that, but I believe its as it was bought from SIP as a worb5 tuned kit.

do you really think the carb might be too small though I have got a PHBL 28 here at the office we can try but I took this pipe because it was the "Road" Version not sport
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What jetting is in the carb at the moment?
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I guess I'm in the never cut camp, but it's your scoot and it's nice work with excellent results. People often maul stuff when they modify it and you obviously didn't.
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orwell84 wrote:
I guess I'm in the never cut camp, but it's your scoot and it's nice work with excellent results. People often maul stuff when they modify it and you obviously didn't.
All my life I was a never cut person and even now with this cut job i felt that I did the bike a disservice but at the same time I really like the outcome so difficult situation for me.
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themod1 wrote:
All my life I was a never cut person and even now with this cut job i felt that I did the bike a disservice but at the same time I really like the outcome so difficult situation for me.
I think it looks great. It's a scooter, not a monument to Italian engineering. Maybe if it was the last one on earth.
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Nice scoot. What model frame did you start with?

I have pretty much that exact bike/setup. I bought it already cut down, so I didn't have to make that difficult decision. I also swapped out the VSP road for a banana pipe.

I'm still coming up to speed on tuning, so I don't think I can help you out there. It's running pretty well at the moment, but a pro setup all the port timings before I bought it.
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Hey guys, Tony here

OK so port timings as well as crank timings are stock, as we got it.

The intake is a malossi Reed valve intake, yet the rotary vane is still intact and functioning. The best I can get her is running without the Reed valve at all, and relying on the rotary vane for intake timing. The Reed valve robs plenty power by opening later on than the rotary vane yet the rotary still shutting early as far as I can tell.

The carb is a malossi tuned phbl25, currently sitting on a 110 main. Our elevation is a rather high 1750m so we often don't need massive jets in our builds. I also felt like the pipe may be too big for this, as it pulls well up to about 6500rpm, and then hits what feels like a 4 stroking wall. If you hold throttle open and push through this for approx 500 rpm, it pulls like a stabbed rat up to just under 10k rpm. You can keep it in this upper powerband with the gearing that has been used, and it does stay cold here, but under the 6500rpm and while trying to push through it the motor heats up fast.

Ignition timing has been set up about 5deg either way from where it is now, currently starting up at 23 and dropping down to about 14deg high up.
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Never heard of anyone be able to keep the rotary working with a Reed setup.

Surely can't work properly.

The rotary crank must stifle the reeds?

I only imagine it could work with a bell shaped crank?

What's the rest of the carb jetting?

Atomiser and needle?
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UTC quote
That's what i think too. You can either run a smaller motor on a rotary setup with a straight intake manifold, or a large setup with a proper crank and big flowed openings for Reed valve.

Can't remember where I got to last time on the carb setup, will check next time I open up
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UTC quote
BUMP

Hey everyone
I have still not had the pleasure of riding this bike other than about 800 odd km as Tony is still struggling to get her set up. I am now antsy to play with this bike.

The following was sent to Worb5 (because the barrel kit is a Polini / Worb5 tuned with GS piston)

Maybe someone here can advise further
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As per email sent from Tony (My Mechanic to Worb5) not had a response from Andy for a few months with follow up emails maybe someone here has more ideas

"Good Day Andy

My Name is Tony, I am the person responsible for building Gerhard Habib's SS90 replica with the Worb5 Polini GS 130 kit. We have been struggling for some time with this bike, and I have now gotten to the point where I feel I have tried almost everything and still the Setup feels wrong.



This is the current setup in parts:



Polini GS 130cc - GS piston, Malossi Head, Polini cast iron barrel

SIP PV style casings

Port matched on side ports, half on 3rd port

JL VSP Road exhaust

Mazzu race crank - 51mm stroke 97mm rod, std disk valve timing

Malossi PHBL25 carb setup, intake changed to a straight intake, not reed

29/68 straight cut gear ratio - 2.34

SIP Vape with variable ignition



Only work to casings has been the port matching, have not played with intake timings yet. I have tried a multitude of different Jetting setups, ignition timing combinations, different thicknesses on the base gasket and still I get a low performing engine, struggling to rev past 8000rpm. It also heats up very quickly and struggles to operate under 150deg celsius.



Do you have any suggestions I can try?



With no spacer under the cylinder, I read 174deg exhaust timing, 110deg intake timing, with the rotary opening at 71deg BTDC and closing at 50deg ATDC.



It must be said, that the previous iteration of this engine was on the stock V9a1m casings, and there I did clear out all the material around the rotary vane and ran a reed valve intake. It made more power than it does now, but had a very nasty misfire between 6500rpm and 7000rpm that was so hard to get past that it could only do it in 2nd gear. It pulled very well over that mark, but the casings started leaking from the gear selector and we opted to rather go with new ones. Would you suggest going back to the reed valve and clearing out the material on the new casings? I am hesitant to do this as it didnt quite work on the previous setup."
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I'd look at a few things:

- port timing seems pretty low. I'd look at increasing those numbers
- how was the ignition timing set? What was it set to?
- carb jetting especially for the midrange… I suspect an area is too lean and one is too rich.
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76 Sprint V, 63 GL, 62 VBB, 05 Stella, 66 Smallstate
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UTC quote
What 108 said.

14 BTDC ignition timing at a "far up" of 6,000 RPM's or so is pretty far off. Should be 18 BTDC at 6K (or whatever your cylinder calls for, but probably 18 with electronic ignition).

But, to make matters worse, with a 110 Transfer Duration, it's going to deliver peak power at like 5,000 RPM's, so it's basically peaking before it ever hits the power band.

While I don't know that having the reed with rotary crank is necessarily a Bad Thing, you're definitely not getting the benefit of the reed, which puts you at the mercy of your intake timings, which are already short at 121 degrees total intake time.

I'd suggest
- a bell crank, which'll give you a little power boost on the low end, (or at least a flowed crank);
- Get your transfer timings up to 124 BTDC or so (even better, get recommended spec's for the exhaust?)
- Open up your intake so the reed can breathe

Once you've done that, you'll now have something worth worrying about the carb on.
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