a few 4.3 chevrolet

i hope i put this in the right section (forgive me if i didnt). so a buddy of mine cracked the head on our 4.3, long story short i replaced the head and put it all back together. only now im having a few problems #1 it doesnt seem like it has the same power it did before, trust me it needs it and #2 its got a little miss. The local mechanic told me the timing should be set at zero at idle which just doesnt seem right to me but im afraid to turn it up to much because we all know what pinging will do for a cast piston.
other information you may need to know is its a 2bbl, we replaced all the plugs, wires, cap and rotor when we changed the head. also im sure the head that went on is the exact same casting # as the one that came off.

you guys always find a way to help.... thanks in advance

Mike,

The electronic conversion kits are probably the best $100 upgrade you could make on that motor. The time you will spend trying to diagnose the issue is probably worth more.

The 4.3 is basically a 5.7 without 2 cylinders, I recently replaced the 4.3 in my 2001 Silverado (had a rod knock). I would expect the timing to be about 10-15 degrees btdc without vacuum.

My first guess would be ignition, determine which cylinder has the miss by pulling wires while it is running (with insulation one at a time). Its possible you have a faulty new wire, swap some wires and see if the miss follows the wire, next try the plugs, try the old cap. If the miss is still there do a compression test. A poorly seated valve can cause a miss and low power. If the compression test reveals a low cylinder do a leakdown on that cylinder. Listen at the carb and exhaust to determine if it is an intake or exhaust valve. Hopefully that's not as you will have to pull the head and lap the valve seat.

Too bad I just tossed my old 4.3 with good heads...