1976 mercruiser 350-loss of power

[jmac]

I recently changed manifolds, and installed new plugs and wires. I was careful to follow the original firing order. After putting the stbd engine back together, it fired up fine, revs up fine in neutral, but has no power under a load. Compression in all cylinders average 135, just 15lb short of the spec.
My first thought was that I had a plug wire reversed, so I went to the service manual. The firing order for my port engine is per the manual, but the starboard was not even close. When I tried the firing order per the manual, nothing. Put it back as before and started and ran fine, just no power under load.
Next try was carb-swapped the carb from the port side, same problem.
Ant ideas what to try next?
thanks......jmac

[In Memory Walter K]

Right hand and left handed motors (if that's what you have) usually have different firing orders (and if I remember correctly, different timing marks). If the changing of prop directions is the result of your transmissions, then they would be the same.

[Carl]

Changed exhaust manifold or intake manifold? If intake maybe your not sealed right and losing vacuum.

Did you check timing?? Maybe Distributor moved a bit playing with wires and timings off...counter-rotating motors you need to keep in mind mark is flipped on one motor ( I know I get confused from time to time) Dont't take much to lose power.

Use the right plugs??? Gapped correctly??

Wires...is it the Premium, "Make Them Yourself Wires"?? if so, they can be a real pain if the connection isn't fitted correctly...you get juice thru the wire...but lose alot, enough to throw power off. My mechanic picked up on that once by checking arc...I thought long as you got an arc it was good, he said it wasn't hot enough. He redid the connection and sure enough a much better spark.

Let us know.
CArl