454 mercruiser mag won't start

[D.doctorick]

1993 mercruiser 454 in a chaparral villain III had water in oil. Tore motor down found bad gasket. Had heads sent to machine shop. Put all back together. Now it won't start. I have fuel. I have spark. I verified timing is correct, 0 degrees tdc for starting purposes.

Boat has cam(don't know the specs), 9.5:1 pistons, 502 heads, roller rockers.

Ran perfect before. Had got it to fire once but it was rough and not on all cylinders.

Thinking it could be valve issue?
Anything will help. Thanks.

 

[Bt Doctur]

What is your mechanical ability rebuilding motors? Did you only do the head work?

 

[D.doctorick]

All the manifolds and risers were pressure tested and cleaned up.

It back fires thru the carb and exhaust also

 

[Bt Doctur]

the timing is off, what is you mechanical ability?

 

[D.doctorick]

I've worked on motors before. Im a maint foreman in a coal mine so I understand what's going on.

 

[Bt Doctur]

Backfiring is usually caused by incorrect timing, incorrect sparkplug firing order, tight valves

 

[D.doctorick]

It was set before at 10 degrees btdc. I rotate the motor over til both valves are closed on number 1. Line the marker to 0 degrees and have the rotor pointing at number 1 tower on the cap. I traced all the wires they match going to the plugs from the distrubtor cap. So that's why I was assuming valve issue

 

[Bt Doctur]

there are 2 firing orders on most dist caps . are you using the correct one for a standard rotation motor clockwise 1,8,4,3,6,5,7,2
I would try resetting the valve lash at "0" lash, get the motor running and do a running adjustment

 

[D.doctorick]

Yea it's the correct firing order. The same one that was on there prior. Right I'm gonna adjust tomorrow and we'll see.