Well I have been setting timing until I am blue in the face and have concluded that the timing cannot be the problem. I have set it everywhere from 34 to 45 total and have come up with the same thing....crap. I noticed that when I was trying to find the total timing the timing light would speed up and right as it got to 2500rpm or so the timing light would slow down to a slow flicker, slower than at idle. I thought the light would only get faster as the revs got higher. Someone told me there is a problem with either my distributor, ignition or both. I have a mallory magnetic breakerless distributor with mechanical advance and a MSD6a ignition. The box is many years old.
Upon dropping this new engine in there was no bogging off idle and it would peel out at ease from any rpm in first gear. With no change the truck stumbles below 1500 rpm, bogs when floored and struggles to rev to 5500 when my combo should be good to 6500. It has lost over 1 second in 1/4 mile times.
What could be the problem? I have replaced plugs, wires, cap and rotor, bushings and springs in the dist., coil. I have replaced all fuel lines, fuel pump and fuel filters. The only thing I havent replaced was the MSD6a ignition which is many years old. Please help. I need to have the problem solved.
Should I just break down and buy an HEI distributor and scrap the MSD6a? Thanks in advance for the help.

 

go to a msd pro billet distributor and new ignition box.

 

My MSD Digital 6+ came from the factory with the Distributor 2 wire harness wired BACKWARDS. Yes...the fool-proof, one-way connector was wired backwards...Made for a big headache, extremely jumpy timing at idle and anything over 3000RPM produced BIG backfires, etc...Fixed it and it revs to 7500+ now but it still cuts out in the midrange pretty bad, hopefully the connector is loose internally or something..Gotta check that soon. Maybe try there. Goodluck!

 

Are you sure that the balancer and the timing tab on the new engine are matched to each other. In other words a 6 1/4 balancer takes a different tab than a 7 inch. Bring #1 up to TDC on compression and the 0 on the balancer should line up with the 0 on the timing tab. Also if you are using a stock style balancer with the rubber isolater they can slip around therefore it would be impossible to set the timing. If all of this checks out I say the problem is in the box. Although most boxes that I have seen fail simply won't fire at all. Hope this helps.