OK so i put a Jp2 pipe on my hyper 21. now when i think i have it tunned right it stalls around mid range. now my engine has a mid range screw but the manual says DO NOT TOUCH but when i got help tunning it the 1st time in feb the hobby shop guy turned it i dont know what to do!!!!!!!

IT SHOULD BE FLUSH

The mid range screw?

As I was told by a fellow offroad racer and a really good one, there shouldn't even be a mid needle on these offroad engines, and yes it should be flush.

The mid range needle only has settings at 45 degrees. You need to take you HSN out and look down the mouth to ensure that the mid speed needle is fully open.
Yes 2 needle carbs are easier, but unless you want to buy one you'll have to ensure its set correctly.
If you can find an OS 20E carb for cheap on ebay they work great.

Don't touch you mid range needle!!! If your engine ran good befor you changed pipes check your glow plug first. Then if the glow plug is good richen your high end needle, sounds like your going lean.

AMEN! RB Concepts don't have them, Nova Rossi P5 switched from 3 to 2 finally. I wish the Vspec would ditch the Mid range screw also! I had a Hyper 8 port and it was the hardest engine to tune I have ever seen! It would scream when you get it right but it was hard to get right. It is very tempermental to temp changes humidity, altitude etc. Like someone said, if you want to run this engine pick up the O.S. RG (20E) carb and slap it on,its worth the $$$$$.

Thanks a lot guys!!!! I hope i get it running good again[]

I just had this probelm and was mystified. Seemed like I was rich on the top end, and rich on the bottom end, but lean in the middle. Kept stalling around mid-throttle. In the end, turned out I had mis-diagnosed things and all that was needed was to lean my LSN.

Luckily that engine didn't have a mid-range adjustment. If it had, I would still be messing with things and not have it right.

By the way, I assume you engine is cutting out at a "held" mid-throttle postion. If it is actually cutting out around 1/2 max rpms when accelerating from a standstill, you probably have too lean a HSN instead.

I know the manual says do not touch mid needle but you MUST make sure the hole in the needle is lined up with the hsn housing. For anyone to tell you not to use it is way wrong and why they do not in the manual describe its settings and what it does is a major clue to me and anyone who knows this engine. Here is the best drawing I have seen to explain it........
http://www.ofna.com/forum/viewtopic.php?t=4339
I also run the Hyper.21 and am amazed at how much power and speed this engine will prduce when tuned correctly. Once you understand this engine it really is a very easy engine to tune and enjoy. Do yourself a favor, once you align the mid needle hole (there are 4) with the hsn housing so that the mid needle face is flush with carb body, scribe the outside of the carb body to match up with your mid needle so you can tell if it ever walks on you.