89 Maxum runs great for 20 Mins then dies?

[Crayfish]

My 1989 maxum which has the 5.0 stern drive motor will fire up every time then run for about 20 or 30 minutes then die. Wait a little while and itll fire right back up. Ive replaced the battery and altenator. Next im thinking a new coil. Any other ideas before I start throwing money at this old boat?

[Phillbo]

Once you get it restarted how long does it run before it dies again?

[Crayfish]

About the same maybe less. 15 to 20 mins. Thanks for the reply Phillbo

[Crayfish]

Not sure if this has anything to do with that problem but after about 15 mins the power trim and tilt will stop working also

[mmwjr]

A clogged fuel tank vent can cause this. Next time it happens try opening the gas fill cap and see if you hear a rush of air and the boat starts then.

[jrsick]

Clogged vent is very likely cause. I've also heard of these same symptoms with a cracked distributor cap. Check inside the cap for moisture when this happens again.
It's always good to replace old parts, but there are checks to determine where the problem is and avoid removing good parts.
You should get a multimeter or a power probe-type tester to help isolate your problem. An HEI spark tester is also a good tool and has been very helpful for me.
Battery check; you should have at least 12.4V static, and the voltage should not drop below 10V during start cycle. If battery passes both tests then it is good and does not need to be replaced.
Alternator: Battery voltage should test approx. 13.5V with engine running. Anything below 13V indicates alternator needs to be replaced.
Spark: Use HEI tester to check for spark next time your problem happens. If you are getting spark then it is certainly fuel related. If no spark then work backwards from distributor to coil to ICM. This test is in Vol 24 (5.0 service manual) in documents section, see "testing thunderbolt V ignition" section. There is also a check for the coil so no need to guess. Let us know if you'd like help checking your systems.

[Crayfish]

Thanks for the replies guys! I ended up replacing the coil and this fixed the problem. Boat ran great for over an hour. Now I just gotta figure out what prop I want. Looking for a good top end speed but also able to pull a ski or tube

[mmwjr]

Originally Posted by Crayfish

Thanks for the replies guys! I ended up replacing the coil and this fixed the problem. Boat ran great for over an hour. Now I just gotta figure out what prop I want. Looking for a good top end speed but also able to pull a ski or tube

Thanks for posting your findings.

[shrew]

Originally Posted by Crayfish

Looking for a good top end speed but also able to pull a ski or tube

These goals are somewhat at odds with each other. Increased top speed will adversely impact the holeshot and vice versa.