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1974 VBC1T
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Hi all. I just did a partial restoration on a customer's 1974 VBC1T. I got it up and idling perfect and seemingly running great. I took it out for a road test today and it seems to hit a wicked flat spot. It pulls good initially then it just falls on its face then seems to pick up good again in the higher revvs. By the time I got back to the shop it wouldn't even idle and it took a while to get it restarted. I replaced a few gaskets in the carb and it's leaking a tad and I noticed it floods when sitting with the fuel tap on so I need to get back into the float system again.

I've worked on tons of Mikuni and Kehin carbs in all sorts of motorcycles, dirt bikes, atvs and watercraft but never these old Dellorto's. Any tips or pointers as far as adjustments and whatnot goes? Thanks in advance.
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I'll just go off a list of things people may want to know. Have you put a new needle and float in for the flooding? What size carb are you running, 20/17 or 20/20? What jets are you running for idle, main, and air, and mixer. what are your mixture screw settings. What's your spark plug look like, and how is your timing? Also, if it floods with the fuel tap on, turn it off when not in use. I usually even run the remaining fuel out of the line before shutting down for the day. I think that'll get you started with some answers. I'll guess if it floods, then you don't have a problem with fuel delivery, but sometimes for me its hard to decide if its flooding or starving.
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Mr. Clean
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One thing to remember Breezy is that the air-mix screw is the oposite of Miks and Keihins...

so on a vespa SI carb like you're working on, in is leaner, and out is richer.
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panchoboots wrote:
I'll just go off a list of things people may want to know. Have you put a new needle and float in for the flooding? What size carb are you running, 20/17 or 20/20? What jets are you running for idle, main, and air, and mixer. what are your mixture screw settings. What's your spark plug look like, and how is your timing? Also, if it floods with the fuel tap on, turn it off when not in use. I usually even run the remaining fuel out of the line before shutting down for the day. I think that'll get you started with some answers. I'll guess if it floods, then you don't have a problem with fuel delivery, but sometimes for me its hard to decide if its flooding or starving.
OK here's what I found:
20/15 Dellorto
Main Jet: 86
Idle Jet: 42
Air Jet: 120
Atomizer: E1
Mixture screw: 1 turn out

Spark plug looks a tad rich but not too bad, although the very tip of the electrode is grayish-white.

I've been turning the fuel off and letting it run for a bit before shutting it down. I'm going to order a full rebuilt kit for it from Scooterworks and go right through the carb.
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Vader19 wrote:
One thing to remember Breezy is that the air-mix screw is the oposite of Miks and Keihins...

so on a vespa SI carb like you're working on, in is leaner, and out is richer.
Well that depends on the carb and where the mixture screw is located. Most street carbs have the screws on the engine side and control fuel flow so in is lean and out is rich. Most off-road and snow carbs have the screw on the airbox side so it controls air and it in for rich and out for lean. It also seems to go hand in hand with the engine - most 2-strokes have air screws and most 4-strokes have fuel screws - most of them lol.
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Breezy,

When you say "customer," what do you mean?
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SFvsr wrote:
Breezy,

When you say "customer," what do you mean?
We are a Vespa/Piaggio dealer, however 99% of the time we work on late-model scoots. We've done vintage stuff occasionally but they don't come around very often. I tried to use "Vespa Leicester" as a username but the forums wouldn't allow it for some reason.
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bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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BreezyBend wrote:
Hi all. I just did a partial restoration on a customer's 1974 VBC1T. I got it up and idling perfect and seemingly running great. I took it out for a road test today and it seems to hit a wicked flat spot. It pulls good initially then it just falls on its face then seems to pick up good again in the higher revvs. By the time I got back to the shop it wouldn't even idle and it took a while to get it restarted. I replaced a few gaskets in the carb and it's leaking a tad and I noticed it floods when sitting with the fuel tap on so I need to get back into the float system again.

I've worked on tons of Mikuni and Kehin carbs in all sorts of motorcycles, dirt bikes, atvs and watercraft but never these old Dellorto's. Any tips or pointers as far as adjustments and whatnot goes? Thanks in advance.
The Dellortos on these scoots are respectable carbs, nobody's idea of hi-tech, but solid once dialed in.

The float needles are notorious for drippage. The red-tipped ones seem to do better than the black-tipped ones. Also make sure the gaskets under the carb and carb box are good, and the carb bolts are snug.

The flat spot sounds like either mixture adjustment is off or main/air jet combo isn't right. For mix, start at 2 1/2 turns out and find a smooth idle from there. As for jets, need to know what size carb, and whether the scoot stock, kitted, piped, etc. to make suggestions.

Hope this helps.

* edit: just saw your set up.

We're running the following on our Super with a 20/15D and it sings:

Main: 88
Air: 140
Idle: 42
Mixer: BE1
Starter: 60
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OK I got the rebuilt kit in from Scooterworks yesterday and got the carb disassembled, cleaned and rebuilt today. I set the mix to 2 1/4 turns and she seemed to go well. Had no problem keeping up with 50MPH traffic (give or take - speedo isn't right). It felt like that was about all she had though, not much more. Does that sound right for a 150 Super?

Also on the speedo - I had sent it out to SpeedoKing because it wouldn't zero and he took care of that. Now I notice that the needle bounces around - more so at slower speeds - but also the road I was on has a 50MPH speed limit and when keeping up with traffic the speedo was bouncing between 70 and 80 and I know that's not right. It does zero properly though. The speedo is OE and the wheel hub is OE but the cables have all been replaced with the PRima units from Scooterworks but I don't think the cable would make it go faster. Any thoughts? Thanks for all the advice so far as well.
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bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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bodgemaster
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Check the speedo pinion, the little piece with plastic spiral teeth that turns the cable down at the hub. If the teeth are gummed up or worn, the speedo needle will bounce all around.

50mph is about all a stock Super will do. They weren't built for speed. Real workhorses though.
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Alright I'll pull the speedo housing off and check that out. Thanks!
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Style Maven
'74 50s x3 '87 PK125XL '92 PK50XLS Plurimatic - & - '58 AllState '68 Sprint '66(?) Super125 and '72 DanMotor Super150
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That pinion is downstairs, in the front hub. No need to pull the speedo. Find a diagram somewhere if you get lost.
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Molto Verboso
'74 Rally, '72 Sprint
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Molto Verboso
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The link here is from SIP and has a good diagram for the speedo pinion. It should be a very easy check and job.

http://www.sip-scootershop.com/main/service/PartsCataloguesDetails.aspx?table=3c847968-edc4-4916-a103-dc239e9da9f4

Saying that, I've had "very easy jobs" that have ended up being the biggest bastard jobs ever! I recently changed my speedo Cables and gear drive and it was not too bad overall. Works a treat now which I find weird. Used to having to guess my speed from non-working speedos in the past.

Good luck.
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I pulled the cable from the wheel housing and everything was clean. I reinserted the inner cable and readjusted the outer cable so it wasn't trying to squish the inner cable when you tightened the nut. It took out 90% of the bounce but now it seems the speedo reads about 15-20mph too fast. I was riding around what felt like 30 or so and the speedo was reading near 50. I'm going to take it out and follow someone at a known speed and see exactly how far off it is exactly.
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bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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bodgemaster
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Vespa speedos are notoriously optimistic. Ours says we're going 10mph when the scooter's standing still.
Forum member supplied image with no explanatory text
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1974 VBC1T
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HAHA this one was a 20 at a standstill before I sent it out to SpeedoKing
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