57 ferguson to35 fluttering and bogging down after short dis

I have just finished rebuilding my 1957 Ferguson to your 35 with a continental Z 134 12 boat engine. I did a ring job honed the cylinders replaced the governor rebuilt the carburetor did a full head joband replaced the plug wires voltage regulator and starting switches. it runs at idle perfectlybut when I take it out the driveway after a few short minutes and bring the RPM's up it wants to start fluttering and bogging down I can back the choke out and push it in rapidly and it will level back off but starts bogging again. I am just trying to figure out what all might be going on. Any help will be greatly appreciated.

Congratulations! You successfully used the choke as one of the simplest and most valuable diagnostic tool available!

The result of the test, it's too lean!

Why is it too lean? Well, since it idles perfectly, not very likely it has a vacuum leak.

First, be sure there is sufficient fuel getting to the carb. There is a drain plug in the bottom of the bowl. With the fuel valve open, remove the plug, catch the results in a large glass container. Should get a full flow for a couple seconds, then slow as the bowl begins to empty. The flow should continue as a stream, not a drip. If it slows to a drip, there is a restriction somewhere, either at the sediment bowl screen, at the carb fitting, or at the needle and seat. Now, look at what drained out. Is it clean? A few grains of rust is acceptable, but if it's got a layer of sediment or water in the bottom, the fuel system is contaminated and will need attention.

If the fuel flow is good and clean, look for the main adjustment screw on the bottom of the bowl. Back out the main jet adjustment a turn or so. A good test for main jet adjustment is to start the engine, set the throttle speed at full throttle. Manually pull the governor to idle, release the gov, the throttle will spring wide open for an instant. Adjust the main jet so the engine will respond instantly with no hesitation. Just a puff of black smoke is acceptable.

Another thing to check, these engines were prone to distributor problems. The shaft bushings wear, letting the shaft move side to side making the point gap impossible to set or keep set. Also the centrifugal advance will freeze up. To check, manually turn the rotor CCW. It should move a few degrees and spring back when released. If it doesn't move or is sluggish to return, it will need to be disassembled and freed up, lubricated. Make sure this is right before doing final fuel adjustments.