ORIGINAL: proptop
Hmmm...ok...
I just went and dug mine out of the box. I have an early .65 Sportster as well. No bushing and the needle is on the carb. I however have an eccentric adj. screw for the brass low speed adj. disc.
If you don't have the eccentric though, what's to keep the disc in place but o ring friction? (similar to Perry carbs )
I'm just thinking that if the disc rotated a few degrees...it doesn't take much...it can effect the entire r.p.m. range, not just the idle.
I have the eccentric screw also. I pulled the low speed disk out and pulled the needle out of its assembly and everything looked fine. while the disk was out, I blew into the pressure line and fuel flowed through very easily, so I fuel flow from the tank is not the issue. The tank is sealed - I used a brand new sullivan 8oz tank to replace the LST tank I was using and I had no change. I am going to pull the carb barrel out and see if there is any debris in the spraybar assembly and if thats clean, then I don't know.. there isnt much to these carbs and why the drastic change in running kinda baffles me.
I dont know if it matters, but the last 4 or 5 times I started the engine it kept starting in reverse... It hasnt done that much since I started it on the stand during break-in. Perhaps I'll go to the hardware store and get a couple new O-rings and see if that makes a difference. I did adjust the idle mixture richer just a tick, that seemed to drop the idle speed down a little bit but it seemed to run okay and throttle up decently but once I hit WOT it just sagged off. I know the servo is opening the throttle all the way and its returning to the idle stop each time you let go of the trigger.
I know the spraybar hasnt changed positions as far as I know - this is pressed into the barrel. When I have some daylight tomorrow morning, I'll take a look at it and see if maybe the spraybar did move. Thats the only other thing that I see that could have changed. The idle mix doesnt get adjusted much because its too rich even at its leanest point. When cutting fuel the engine, the engine will idle for several seconds (5-10 seconds on average) before it stalls. It does not speed up or down, it just very slowly slows down a little bit until it just quits. At this adjustment, its in the full lean position.
There is something amiss with the engines the military used on their Drone target planes that used these engines but they are ran WOT and thats it. I think there is a fault with the size of the spraybar orifice and/or idle mixture orifice. The orifices line up perfectly when installed in the carb, I just dont know if they were mis-cut when manufactured or what.