First let me describe the problem and then I will give the engine particulars. My problem is very “lumpy” performance below 2000 RPM. Acceleration and deceleration are fine but the car does not smoothly hold a constant speed. Above 2000 RPM the performance smoothes out but remains irregular. It acts like there are ”bumps” in either the engine torque or fuel delivery. In August Vimto (20524) described a similar problem. Motorbill66 suggested three possible causes, which I address below, but the thread never finished so I do not know if or how the problem was resolved.
My car is a rubber bumper MGB (stamped 1979) having LE accessories. I have reason to believe that the engine is not the original motor and it has certainly been rebuilt; i.e., an old parts list shows a Crane cam, compression is uniform but high, and the distributor is a 45DE4 usually found on ’78 or ’79 engines. I just replaced the 45DE4 with a new Pertronics Flame Thrower distributor. The carburetor is a manual choke 32/36 DGV which I have just rebuilt using kit parts. To avoid vacuum leaks I carefully torqued the carburetor down (with new gasket) to a rigid (not flexible) mount. I think that the two carburetor problems, discussed by motorbill66 have been eliminated. His third suggestion was “poor fuel delivery,” that he stated was “easily checked.” Can motorbill66 or someone help me with this measurement?
Other than the fuel delivery problem I have run out of things to try and would appreciate any new direction.
BobK