I'm not sure if this is carb related or not, but here goes. I have an 87 Trans Am, originally an LG4, but it does have a 350 short block swapped in with all the factory 305 accessories and hardware. Other than a tuneup, a cheesy add-on electric fuel pump (on my to do list) and the removal of the smog pump, its completely stock. It drives fine, but between about 1200-1500 rpm there is a vibration. It shakes the dash, door panels, steering...everything. It does it whether the car is moving or not, and remains as long as I'm in this RPM range. My buildup the next few months (cam, heads, intake, carb, distributor, headers, etc) will probably inadvertantly fix the problem anyway, but I'd like to figure it out and fix it before that. Any ideas?

 

Probably an engine balance issue; either a bad harmonic balancer, out of balance flywheel, unbalanced torque converter, improperly balanced crank & rods, etc.

 

Possibly a loose or missing convertor bolt? From the loose fasteners I have discovered on this car I wouldn't doubt it. I'll check the balancer, too...internals will have to wait til I build the other motor, unfortunately!

 

Check your mounts while you're at it, especially the transmission mount. Amazing what a broken piece there will do.

 

MY car does it at an idle at a light or stop sign\

but i think its the trans mount.