BryanZ

I need someone with Mercruiser 7.4 experience. Port engine not running on all cylinders. Here is the history. Had a frozen valve on cylinder 4 had the head machined and new valve guides installed. Reinstalled the head 2,4,6,8 side. Not my first rodeo with this, my boat has had reversion problems in the past. Adjusted valve as per merc manual, Mark IV big block. New manifolds, wires, rotor, cap, plugs oil change, the usual tune up rebuild. Compression test 120 on all 8 cylinders. She started right up after rebuild. Here is were my problem is and im not sure where to go from here. With a timing light she wont even run unless im at 16 Degrees BeforeTDC. In order to make power, When i turn the distributor counter clockwise she runs better moving the time mark well past the markers up toward the water pump but still doesnt run on all cylinders. I check TDC and it lines up on the balancer and piston 1 is all the way up so i assume it is correct. You can pull the wires on cylinder 2 and 5 there is no difference while running. (again i have 120 compression across the board) I have checked my wires 50 times and im getting spark.
I dont know what else to do at this point. I cant get the timing correct and she isn't running on all the cylinders.

HELP HELP HELP!!!!

Griff

This is a carb engine with Thunderbolt IV ignition, correct????
How did you get reversion on a stock 7.4???
Have you checked for spark specifically on #2 and #5 ??
Really no way to not get spark on just 2 cylinders with TB IV unless cap, rotor or wires is defective. New parts can be defective.
How did you check for #1 TDC?? Is it possible that the distributor is installed 180* off??

liberator221

Cam lobes all good, since you had a stuck valve? Vac leak on #2or#5 runner?
No idea on timing. Does TB have mechanical advance? Having to advance timing to compensate for stuck advance weights?
I to find it odd that you have reversion.

underpsi68

Spark plugs also

PARASAIL941

Not asking a stupid question , but Merc 7.4 Bluewaters come in reverse rotation.

BryanZ

All fixed runs like a top. turns out didn't have cylinders 2,3,5,8 running which is the left bank of the quadrajet. Seafoam and and some carb cleaner and with in a few minutes she started running perfect perfect perfect!! first time experience for me but another lesson learned

3pointstar

Glad for you

3pointstar