Carb Trouble

[adam0801]

Hi
I have a Derbi GPR 125cc. It has the same engine as the Yamaha tzrr 4DL.

On my bike i have a 28mm mikuni carb with a 210 main jet i also have a gianelli exhaust non cat.

I have just bought a 32mm deleroto carb off a tzrr 4DL from a breakers yard, it has a 120 main jet init.

I really need to know what you think would be a good jet size for the 32mm delertot thinking about my mods. I have been told a 145 might work but any help would be great.
Also what notch on the pin should i start at??
Cheers

[WebTone]

Thje 145 jet will most probaly cause the bike to run rich if you do not change anything else. Check the plugs for signs of this.

To find the ideal main jet size, the needle should be started out on the lowest clip setting which gives the highest needle position and hence the richer mixture. In order to isolate the main jet, the needle jet hole needs to be as large as possible. When the needle is at it's highest position, it must provide at least as much clearance as the main jet, or the main jet size would not be getting tested. In other words, when the needle is fully lifted by the slide, thehole must be at least as large as the size of the main jet for any testing of the main jet to be effective.

Position 3 is likely to give you the best overall performance, top end low range and fuel economy. Many needles fitted in other countries have only one setting which is this mid-point to stop you from fiddling. You can bypass this using small washers as shims if thats the case.