VNB 125 to 150 cc

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VNB 125 to 150 cc

Postby bschulz » Thu Jun 21, 2012 10:57 am

Hello,

I have a VNB but the cyl was cracked.
So i purchased a new one but they only had a 150 kit so i purchased it.

My question is this.
I have the stock carb with all stock settings and jets.
BUT looking at the 150 scooters like a VBB, they are running different jets and stacks.

can I just upjet or should i convert the stacks to the VBB settings?

also, the timings look different from a 125 to a 150.
125 states 26 degrees
while the 150's have 2 settings depending on the model.... either 22 deg or 28 deg.
What timing should I use? 22, 26 or 28?

thanks!
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Re: VNB 125 to 150 cc

Postby JSharpPhoto » Thu Jun 21, 2012 2:39 pm

You will have to adjust your timing for the new jug anyways. I would set it up like a stock VBB in every possible way, and then tune accordingly.

Is that a 20/15 or 20/17 carb?
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Re: VNB 125 to 150 cc

Postby bschulz » Thu Jun 21, 2012 2:57 pm

Its still the 20.15 carb...

so the whole stack of diffuser/main air/main jet thing is not that clear on where to start.
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Re: VNB 125 to 150 cc

Postby JSharpPhoto » Thu Jun 21, 2012 3:45 pm

you should try and pick up a 20/17 or 20/20 carb. if you can get the 17, i would jet it like a stock VBB. If you can get the 20/20 (a better option overall, should you want to run a pipe or higher revving cylinder later on) jet it like PX150E (1984 version).

Keep in mind, these are just starting points. You'll still have to actually tune your carb by doing proper plug chops.

Keeping your original 20/15 carb and running a 150 jug, isn't impossible, but you'll have to do a lot more leg work since it wasn't ever a documented combination by piaggio. If I had to guess, i'd start with the VBB jetting, and keep working my way leaner until it doesn't bog to much. Again, all of this is speculation.

What part of the world are you in?
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Re: VNB 125 to 150 cc

Postby bschulz » Thu Jun 21, 2012 3:55 pm

Thanks for the info!

I do have a 20.16 off a 150 super that I could drop on it..... that's the cheapest way to go.
I was trying to avoid purchasing a new carb but might try it to eliminate some of the potential problems.

and yes i will purchase the 1000's of jets needed to fine tune it in ! Why do I have soooooo many jets... dellorto, bing, mikuni.... they are like little nuggets of gold!

I'm actually in Providence RI where there are more mopeds than scooters....
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Re: VNB 125 to 150 cc

Postby JSharpPhoto » Thu Jun 21, 2012 4:30 pm

i would use that 20/16 and jet it like a super. I can never remember if those older small carbs are air corrected in the carb, or in the jet.

snap a photo of the top of the carb with the air filter removed. it will determine which idle jet you need.
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Re: VNB 125 to 150 cc

Postby bschulz » Fri Jun 22, 2012 7:39 am

Will do. it will be over the weekend so monday I will have it up... thanks again!
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Re: VNB 125 to 150 cc

Postby bschulz » Mon Jun 25, 2012 7:51 am

Just a follow up post on this....

over the weekend I put the 20.15 back on the scooter. put the original air mix and diffuser 150 and a E1.

I up jetted from 82 to 88. plug chopped 2 times and running good.....

Interesting problem I was having completely independent of carb settings.
I was watching the points actuate when running and it was like a fireworks show at the point of spark.

I actually re-replaced the points and condenser figuring that eliminate all possibilities. BUT the yellow wire (solid copper not stranded)from the magneto coil which connects to the points was the issue. it had a break in the wire due to over bending over time. haha!

Fired it up and running like a dream... did a plug chop looked milk chocolaty!! fueled up and cruised 25 miles around Newport RI for kicks!

cheers!
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Re: VNB 125 to 150 cc

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