Hello all. I'm new here, but don't know where else to turn! I'll try to be brief, but I'm having a serious problem with my 4160 after a rebuild.

Like I said, I'm running a 4160 with vac secondary on a 258 straight six, on a Jeep CJ7. This is the carb that came with the jeep, but it was running a bit rough, so I decided to rebuild it. After taking it off, I discovered that the previous owner had removed the fuel transfer tube, effectively reducing the four barrels to two. I also discovered that one of the Venturi on the secondary side was broken off, so I ordered a replacement "core" from eBay and a new tube and added it to the rebuild. After cleaning everything and rebuilding / installation, I cranked the jeep and it idled beautifully!

Now, to the problem. Like, I said, it idles fine. And it accelerates fine. To a certain point. At around the throttle half-open point (I don't have a tach, so I don't know how many RPMs) the engine starts to cough and if I go any further it dies. The vac secondary has not opened at this point, but if I manually move it open a bit, the RPMs will increase, but it starts to backfire. I've done a bit of troubleshooting, but have had no luck. Float levels are OK and I cannot find a vacuum leak, but that's not to say there isn't one. I bought a vacuum gauge today and vac appeared to be normal at idle.

I don't even know what to check next. I'm relatively new to the world of carburetors! Any suggestions?