1975 Merc 850: No start- new CDI, rebuilt carb, spark

[307duckhunter]

I have a new to me boat. 1975 Mercury 850. It sat for years prior to buying it. It started right up and I drove it around my pond for about 5 min. and then it died. It has not started since.

Cranks: No start
Has strong spark
New CDI control box
Rebuilt carbs
New Main wiring harness (motor to ignition)
New plugs and wires
Good compression, all within 5%
Fuel bulb stays firm after prime
New battery
Piston 1 at TDC matches flywheel mark for same

It seems that it must be a timing or fuel issue? Any ideas are welcome. Thank you!!

 

[racerone]

Check distributor belt timing.

 

[Chris1956]

If the timing belt has it's teeth, it is likely clogged carbs. Stick a timing light on #1 cylinder. Advance the throttle until the carbs are about to open. The timing at this point should be 4-6* BTDC.

 

[307duckhunter]

Thanks guys. I’ll check as soon as my bucket of water is unfrozen. I forgot to add that it’s a jet drive.

 

[Chris1956]

Did you replace engine wiring harness? If not,it is likely time. Look for insulation falling off the wires.....

 

[Faztbullet]

You state strong spark but will it jump a 3/8 air gap, if not it wont fire under cylinder compression.