Originally Posted by grizz1

Hi Chipo - I think the key word is ¨significant¨ drop in RPM. If it just steadily gets slower and slower over time, not a problem. When it drops markedly after a short while, this is normally a sign that the LSN is too rich.
If you have a long LSN carb and your HSN is set at 1.25 turns in as you stated in a previous post, this seems way too lean on the HSN. That would be why your motor goes crazy when you lean the LSN. The HSN is like the water pipe coming into your house. It sets the total amount of water you can get. The LSN is like your tap. It sets what you get out of the tap when you open it. If you crimp your incoming water pipe (lean HSN) you won't get anything out of your tap (lean LSN) so thready rapid idle when you screw the LSN in. Are you sure your idle gap is correct ? Sounds like too wider idle gap being compensated by an overly rich LSN and lean HSN. Engine runs OK but will lean bog on a low tank and have that classic ¨load up idle¨ situation.
I may well be wrong, but the LSN tuning method I mentioned works very well for me. My 7 port runs awesome with great temps when tuned this way.

I have long needle carb. HSN 1/2 to 3/4 max in from flush. LSN 2 1/2 to 2 3/4 in from flush. Will run strong all day at these settings.

How old is your engine? If it is new, or has less than 1 gal through it, it will lean bog if you run it even just a tad lean on the HSN when it´s still tight with the long needle. Read break in article on bottom of page 78 and tuning tips by MMods and Retro RC on page 131.

Your idle will increase when you lean the LSN, thats normal. Get everything set for performance then lastly reduce the idle using idle screw if needed to where you want it.