mercury thunderbolt 500, what year, and running issues

[plaer]

Serial number 7089672, what year is it? Also, when it runs fine, it runs great, but, often it will lose power under load after half throttle, does it have a fuel, pump, fuel filter? Its not too trimmed, ive tried giving it choke and pumping the ball when it does it and no help! PLEASE HELP!

 

[Nathan Bond]

Please double check the serial#.

 

[plaer]

I double checked it and think its a 1977, so what about the running issue?

 

[racerone]

Do a compression test first.----Then check for spark that will jump a gap of 3/8" or more on all 4 cylinders.----Have you installed a new impeller in the waterpump ? -----Have you checked for overheating ?

 

[plaer]

Would compression be an issue if its a intermittent issue? Spark is seems strong, I havent installed a new impeller, and I dont think its a overheating issue as it does it hot or cold and water seems to be pumping through well. It almost seems like its rumming on the lower two cylinders, where is the fuel pump?

 

[plaer]

I have intermittent no spark on cyl 2, anyone with a wiring diagram or diagnostic test chart?

 

[plaer]

I tried to get one through the forum, but all I get is 404, file not found?????