1983 Supra Rider losing spark when warm

[83SupraRider]

I have a 1983 Rider with a 351. On memorial day it died on me. I found out it was the fuel pump. I decided to replace everything from the gas tank forward while I was at it, new anti-siphon valve, new fuel lines, new fuel filter, and new fuel pump. Solved my problem the boat started. Problem is it has ran like crap ever sense. The boat will run great when I launch from the ramp, run great for awhile(30-60 min). Then it falls flat on its face, it won't idle, give it throttle and it will die, I can usually keep it running at higher RPM, but it runs poorly. Trouble shooting I found there is no fuel problem. It is electrical, I will have equally weak spark to all plugs when this happens. I have replaced the coil, new electronic ignition, new cap, new rotor, new plugs, wires are still good, I did have a problem with the alternator so I replaced it as well. I have great spark from the coil to distributor, but not distributor to plugs. Again this only happens when it is warm and we have been running it for awhile. I adjusted the timing, checked wires over and over, I'm stumped! What advice do all of you have? I see these symptoms on the forum frequently but I haven't seen a diagnosis that will help me. Thanks!

[michael hunter]

Where are you getting all those parts? What brand of electronic ignition are you useing? What part of the country do you live?

[83SupraRider]

Pertronix electronic Ignition, Accel super stack 8140 coil, marine alternator with internal voltage regulator, I live in Indiana. All parts ordered through marine supply and our original replacements. The boat did have points on it prior to me replacing it with the electronic ignition however it did run exactly as it does now with points. The old voltage regulator was removed due to the new alternator having internal voltage regulator. Ceramic resistor is bypassed with both purple wires going to one post.

[83SupraRider]

Anyone? Anywhere?

[83SupraRider]

Had it out last night. An hour and a half in same old problem! What the heck is going on? I'm driving myself bonkers with this one.

[michael hunter]

Next time it happends loosen the gas cap and see if it helps . Maybe a vent issue?

[OVERKILL]

When you say weak spark, do you mean what you see is sort of a weak amber spark vs the sharp blue you get when it is cold?

[83SupraRider]

A weak amber spark.