20mm CVT carb, which jet?

[theswede]

Hi guys,

Winter's finally given up here, and I am starting to fiddle with my scooter again.
A couple of months back I bought a 20mm CVT carb of Autotech on ebay (see my previous post called "Two fuel lines to the carb" for pics) and I am now about to install it when I realize I have not got any idea which jet size I should start with.
Currently I use a #90 jet and a free-flow filter on the original carb and it runs extremely well with the proper spark plug color.
The new carb came with a #98 jet, and I have a set of spare jets ranging from #88 to #108 in size.

Any hints on this would be most appreciated.

/Otto

[Rebel]

Boy, to know that it seems you need to know the airflow in comparison to the old carb. The more the airflow the bigger the jet you would need. This is all based on the bernoulli's principle as I recall.

[shiftless]

I'd start with the 98 that came with the mixer

When in doubt... always start rich and go down to be safe

[Rocketdog]

I'm with Shiftless. Even though I think a 98 might be too large. So you went from a stock 19mm to a 20mm. Unless you've changed something else, I would keep it close to the stock jets. They ran well before and 1mm is hardly anything.

RD

[theswede]

Thanks guys,

The stock carb is a 18mm, going up to a 20mm means a 20% increase in venturi area if my math serves me right.
I did find some posts on a Swedish forum about people running #92 jets in 19mm CVT carbs of the same model, so I believe a #98 may be too large.
But better safe than sorry, my setup is not standard which I believe those 19mm posts were referring to (see my tag line for details).
I'll start with the #98 jet and see where that gets me.

Otto

[Rocketdog]

Stock wasn't exactly what I meant. A poor choice of words on my part. I mean try the #90. All your changing is the carburetor size. You say the the plug reads perfectly now. You asked for suggestions. By all means, use a #98.

RD

[theswede]

Ok, now I understand better what you meant RD.
Since the #98 is already in the carb I might just as well begin with that.

Otto

[theswede]

A somewhat late follow-up post on this; after a lot of testing I ended up with a #92 jet.
The new carb offered some improvement in power. Top speed remains about the same, but I get there faster.

/Otto

[Rebel]

getting there faster is good.