I have owned 5 new 10mm carbs. One was on a 40, two on 60 LS's, and two were purchased separately. None of the 5 workedcorrectly exhibiting the symptions metioned here. Isent the Rossi 40 back to Italy and they replaced the carb with an 8mm carb, which works fine. The 8mm carbsas far as I know have not been a probem. They sent replacement carb bodies for the remaining 4-10mm carbs. One works fine, the others are the same. Rossi acknowledged the probem and sent me three replacement carbs. The problem is is still there in the replacements.

Ihave discussed this and exchanged e-mails with the importer (SG)and he has been very cooperataive and helpful. He has been communicating with Rossi, sending them my e-mails and pictures.

Following are some of the findings:

1. In the initial run of carbs and replacement carb bodies, the spray bar notch is not consistantly located in the spray bar, resulting in the tip of theidle needlebeing locatedat different locations in the spray bar notch when fully closed (carb body fully open, idle needle fully closed).
2. Iwas sent new idle needles, which were the same size and lengthas the originals.This did not help.
3. Ihaveattempted rounding the end of the idle needle with mixed results.
4. Various idle needles work correctly in the one10mm carb that works properly.
5.Possiblities as to the source of theproblem (my opinions)are; 1, The spray bar notchis in the wronglocation; 2, The inside diameter of the spray bar is too large, not blocking enough fuel at idle/mid range; 3,The taper of the idle needle needs to be changed.

To clarify the symptoms, the idle/mid range is rich up to and evenwhen the idle needleis bottomed out in the clockwise position. This affects the high speed needle by closing off the spray bar notch to the point where the high speed needle can be backed out all the way and the engine is still lean. When backing the idle needle out a small amount, there is a small window where you can get a clean idle transition with an adjustable high speed needle, but the idle time needs to be no longer than a few seconds, or the engine will load up.

I have copies of e-mails from Rossi to SG regarding plans to send new (longer) idle needles. They plan to test prior to shipping. If anyone is interested, I will post results when I receive the new parts. Ican also post pictures of the different spray bar notch locations if interested.

Jim, the idle needles cannot be backed out for removal. To remove the idle needle, the throttle arm must be removed and the idle needle turned clockwise to remove. So they cannot back out on their own.

SpeedRacer, I tried your technique, but have the same idle/mid range problems. The engine spits fuel out the carb when it loads up. Pinching the fuel line cleans it up.

Has anyone documented the improvements of theVP modifications? Thanks.

Danny