Gremlin 1985 sundancer twin 260’s

ddmusser

Member
Aug 14, 2018
37
West Michigan
Boat Info
1985 sea ray sundancer
Engines
Twin 260 alpha drives
Hello all. Here is what I have going on. 1985 sundancer 300 with merc 260’s. For the first 1 1/2 hours the boat performs awesome at any throttle position. Then after 1 1/2 hours of continuous running, mostly cruising at 3200-3400 rpm’s the boat suddenly drops down to 3000 rpm’s on the starboard engine only. I shut it off wait 30-40 minutes and no issues. So, I have had a total tune up, distributor cap, plug wires, plugs, fuel water separators blah, blah, blah. Timing set, all complete. Motor has about 700 hours and is strong, it seems to be a heat issue, the mechanic has gone through all the cheap stuff first, says it has to be electrical. Has anyone experienced this gremlin before? My thoughts are: coil, cam module, or thunderbolt IV ignition, it only happens after about 1 1/2 hours of running, I know that at 3000rpms the timing goes full advance. So what could be causing this? Thanks in advance. Need some help.
 
Can you push up the throttle and get above 3000 or is it maxed at that point? Does it run rough after the rpm drop?
 
Can you push up the throttle and get above 3000 or is it maxed at that point? Does it run rough after the rpm drop?[/QUOTE. If I push the throttle forward it does not increase rpm’s I would say it surges at the rpm drop, if I bring the throttles back when it happens I can hit 4000 rpm briefly, then the same issue, falls back to 3000, if I let it set, turned of the motor for about 15 minutes it’s fine again
and yes it does run a little rough
 
Sounds like a coil or ignition module breaking down when hot.
 
There is a pickup inside the distributor that can go bad on the Thunderbolt IV. I replaced both mine on my 89 300. They are fairly cheap. Basically a Hall Effect sensor, takes the place of points.
 

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