Modern Vespa

2004 low mileage ET4. Original Walbro died and I have replaced with a slightly larger (29mm vs stock26mm) presumably Chinese Keihin and a free flow K&N filter. Runs great and definitely stronger EXCEPT that it won't take full throttle no matter what main jet I use (stock Walbro is #82 and Chinese Keihin is #118. I've tried everything from a #85 to a #130. All that I've read over the years say that the main jet alone controls mixture at full throttle. I've successfully rejetted and tuned a number of this type of carburetor over the years, so I don't get why I can't make this work.

HELP!

to me it seems like it might be a little lean...maybe raise the needle (lower the clip one notch)

Jixaw: As I understand it, the needle controls the mixture throughout most of the midrange, but when its fully withdrawn (which it is under full throttle) it has no effect. Anyway, I did try shimming it and it didn't fix my problem.

does it pull good idle to 1/4 and 1/4 to 3/4 but bogs out wot?

The free-flow filter may be the culprit. I'd try going back to the stock airbox.