Scooterotica

ok so just built the 225 rt with bgm/mb clubman and 28mm Keihin carb with breathsweet filter, it wont start with the breathsweet on but runs without it, carb settings are 140 main 45 pilot and jjh needle 2nd clip from top.

anyone any ideas ?

Take the filter off

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yeah didn't really want to go down that route, too messy and can drag sh*t in.

I'm struggling with exactly the same issue. The breathe sweet actually evens (leans at peak) out the fuelling and makes more peak power on the RT with that carb but I couldn't sort out starting. I guess the breathe sweet needs a valve/dripper like the standard hoses to allow the excess fuel out so might have to glue one in if I can find one.

BTW that main jet is probably much bigger than you need

That pilot seems way too big, I would try a 38 or 40 and see how it goes. Re the spitback issue that Speed Demon mentioned, plenty of scoots suffer from that problem. Others have tried the drain valve idea without success and others say that a 1mm hole in the bottom of the elbow will do the trick. I, like others' learned to live with it by always turning the fuel off just before stopping and then leaving it turned off until the engine was re-started. Only a problem for re-starting when the engine was warm.

I'd agree on the smaller pilot, hard starting should lie within that part of the carb and it does sound big. I'm currently running the smallest PWK pilot I was able to find and it has improved massively starting as well as the entire range.

Could it be that the problem lies elsewhere? Hard starting when warm normally indicates electric problems such as coil, condenser etc...

This is what I'm running at the moment: http://scooterotica.org/forum/viewtopic.php?f=9&t=26597
So not a million miles from your setup, just a bit smaller on both jets and I don't have a problem with starting with the filter on.
As others have said your setup does seem a bit on the rich side, I've feeling mine is still a bit rich which I have yet to confirm with some plug chops.
Another possibility, how many turns out is the air/mixture screw, it works the opposite way to a lot of dellortos.

^... starting point.