I have a weberized 85 Brat with the 3 speed auto transmission. After a couple months I finally got it running. It idles kinda rough and i have to keep the timing fully retarded (literally) or it will stall out, but it does idle. I believe that there are no vacuum leaks so it shouldn't be that. My main problem is that it idles at about 1K and revs fine, but as soon as its put in gear the RPMs drop to about 500 and it splutters and shakes. If i give it any gas at all while its in drive or reverse it dies, no matter what i do. It seems as soon as a load is being put on the tranny/engine it dies. Does anybody know what would be causing this?

vaccum leak

 

Possibly to the modulator in the trans.