VHSH 30 leaking from vent at low rpm

Looking for ideas here: the issue is that my TM R1 is having trouble starting, when it does it keep leaking a ton from the vent tubes of the carb. A lot, until I hit med/high RPMs. Consumption is super high and black spark plug, so something is forcing too much fuel in the bowl. I’m running a Mikuni DF52-82 pump.
So I took the carb out, cleaned and inspected everything - no issue. The usual suspects (hole in the float), float needle and seat etc were all ok. I changed them anyways with a new set, reset the float level as well. Same problem as before. Plumbing works, no pinching in any fuel line. Return line is free of any obstruction.

My thought at this point is that I have a faulty fuel pump…meaning too much pressure that overrides both the needle and the return line. Strange because that pump has a pressure relief valve, has run about 4 hours since new. Has anybody experienced something similar?

This is interesting, swapped fuel pump, same issue. Now it must be the return line then. Tank is vented, no pressure buildup. Stay tuned

Can’t say I’ve had that issue with the Mikuni pump. My first thought would be float issue, and/or needle/seat. Have you confirmed that the needle is completely sealing? Float arm assembly isn’t bent/broken/burred in a way that would cause it to hang up?

Could it be related to the return regulator?

Absolutely, that’s why I changed the set, they are all new and working, sealing properly. Return regulator is my next thing in line, I’ll bypass it and see what happens

Solved! Indeed, it was the return regulator. It was not blocked, but even on the fully open position was restricting the flow just enough to cause an issue. Thanks for the good idea! Tomorrow’s track day is saved, I will take the regulator apart in the weekend to figure out what caused this. Never had a problem before

Wow! Very curious to hear if you find anything once you take it apart. This has me a little worried as I just purchased one of those to use for next season, so I’m curious if there’s something I need to look out for.

What’s the “return regulator”?

Just worked out the answer to my own question. So, leaving aside the latest issue, how have you found the regulator? Does it make a meaningful difference and what sort of effective jet range do to achieve? I’m interested in particular for very fast long circuit running (as in Phillip Island is super tough on stock KZ engines with relatively very long stretches of WOT, including in 6th down the main straight and sticking a piston can be a nightmare).