5.0 Litre Mercury Mercrisher engine backfire (won't start)

[NathanN]

Hello, I have a 2001 Bayliner 195, 18ft project boat.
MCM 5.0 Litre Thunderbolt V Ignition
Before launching the boat on the lake I did a few dry land tests and everything looked like it worked, Shortly after launching the boat and letting it idle for a bit I slowly accelerated to the max speed of 10mph instead of 40mph... To my surprise this wasn't the only issue, The engine was vibrating the entire boat and making an unusually loud noise instead of a smooth engine noise. after parking it on the trailer I inspected the engine thoroughly and was left scratching my head, After being suggested it was the spark plug wires not being in the correct Firing order I did some research and Adjusted them accordingly but here is where I messed up, After switching the placement of the cables and cranking the engine IT DOESNT START, I've been getting backfires each time I crank it so I'm at a loss
(I tried undoing what I did but ended up getting confused and just left it as is)
Here's a picture to reference what I have set up right now.
Firing order 1-8-4-3-6-5-7-2

I have a Mallory Ignition Distributor, The 8 wires connecting to the spark plugs look in good condition.
If anyone is curious, There are New shift/throttle cables that were Adjusted correctly, New spark plugs, Gas pump, and filter, same goes for oil.

 

[dubs283]

You have a thunderbolt ignition with a Mallory distributor? Something isn't right.

You posted the correct firing order but you need to verify #1 cylinder TDC compression, then arrange the wires on the cap accordingly

 

[Eric 3.7LX Alpha 1]

When you change spark plugs and their wires, do them one at a time to help avoid any confusion where they go. When you change the distributor cap, also just pull one wire off one cap and transfer it over to the other cap one at a time.

What you have looks correct for firing order and cylinder location, but, the #1 cylinder doesn't have to be in that spot on the distributor cap. Any spot could be set up as #1. You'll have to confirm which is #1.

Remove the spark plug on the #1 cylinder, have someone bump the key in very short bursts, a second at a time, while you have a finger over the spark plug hole. You will feel compression at some point, air will push at your finger. Stop cranking. Look at the harmonic balancer, continue cranking in bursts until the pointer lines up with the timing mark on the crankshaft pulley. Now remove the distributor cap and see which wire on the cap the rotor is pointing at, or closest to, that would/should be the #1 cylinder. If your wiring is off, you'll have to move them starting with the new #1 and moving clockwise along the distributor.