2001-951cc That strange 4k rpm drop out

[drjack]

Our 2001 Sportster LE has this occasional rpm drop when running around the 4000 rpm range steadily for about 5 mins. I can momentarily increase or decrease the throttle and return to this rpm and all seems fine for another 5 mins. The rpms just slowly lower to 3500 to 3700.
Carbs were rebuilt last fall with OEM kits. Compression is approx 130+ based on my guage. Plugs and cylinder crown burn ,using fiber optical cable, looks normal
What rpm do the RAVES kick in?
Can the "spring of the pop off" carb diaphragm be too weak, or too high?

Any other rpm, the machine runs great. It's just happens somewhere within this 3800 to 4100 range.

 

[dieselndoo]

Make sure the water regulator knob is even with the cap. Also, make sure the rave valve knobs are 3 turns from bottom out...also want to say, the exhaust manifold has a "play" into that rpm range. An upgrade is 97gsx ltd (grey manifold).

 

[drjack]

Actually, it's happening around the 5000 rpm range. Since my response was thoughts of RAVE or water valves kicking in/out, I'm not as concerned.
Anyways, had a great day out on the water yesterday. Wish this weather could stay for many months more, but Canadian winter's dictate something else.