Help 1985 GM 350 ignition probs

"1985 GM 350 5.7 litre and for

"1985 GM 350 5.7 litre and for some reason they are calling it a 260?

It appears through the manual I have the thunderbolt 4 ignition system.

It idles OK, starts OK but under a load I have significant power loss. In full throttle there is backfiring through the motor, not alot, just a pop or 2. The first time out it ran fine but towards the end of the day I though I noticed a bit of power loss but there was no backfireing. Second time out there was power loss from the start and when I tried to nail it there was the popping so I just backed off. Also there seemed to be possible surging, not noticable in the speed but to the ear.

I changed the fuel seperator before going out the second time and there was a bit of water inside but the filter at the carb was clear and clean.

The sensor wheel appears to show no wear but the sensor itself seemed to have a bit of a rusty color at the pickup point but I have no idea what to look for.

Any possible help will be greatly appriciated.

Jeff"

"Is your ignition maintained,

"Is your ignition maintained, cap, rotor, wires and plugs?"

"Well, mostly. The cap appeare

"Well, mostly. The cap appeared to be in decent condition although I cleaned all the contacts (not much build up). The rotor also seemed good and cleaned that up as well (no build up). The plug wires also seem in good shape although I did not inspect them too closely.

I replaced the plugs with RT44's, I believe, for a regular (non marine) chevy 350. They seemed to do well the first day out but after reading further in the manual it stated clearly not to use reegular automotive parts.

The Thunderbolt 4 igniton is what threw me, I have never seen a distibutor like this before.

Anymore help is still greatly appriciated. And a free place to stay for a fish trip in Louisiana.

Jeff"

"The automotive plugs will wor

"The automotive plugs will work well, the main difference being that the marine plugs are made to be more corrosion resistant alloy in the steel base. In either case using anti-sieze on the threads of the plugs will help prevent problems with getting stuck with corrosion.
Distributor cap and rotor should be changed regularly, not beyond 2 years especially on a boat.
Spark plug wires can last a long time especially good quality ones. They can though be damaged easily any time you handle them or might have a weak connection at the time that they were manufactured. If you can't remember the last time they were replaced I recommend that you invest in a new set. I suggest high performance, street legal ones ( Accel, MSD ect. ).
Bring the ignition up to snuff and see what happens."