Engine: 2003 Mercury 75hp 2-stroke ELPTO
Issue: The engine will idle easily but surges after about 30 seconds at anything above half-throttle. The longer it idles, the longer it will run at higher RPMs, but it will always lose power-- to the point where it almost shuts down at WOT. It will often "surge" revving up and down while in gear--without any adjustment to the throttle.
Background: This engine sat, fogged and shrink-wrapped, for about 5 years, until I starting working with it this year. Within the last month, I have replaced the fuel pump, fuel filter, water pump, and spark plugs. Compression is 110 in each cylinder. I also cleaned the carburetors and replaced most of the fuel hose. The carburetor adjustment screws are set 1 1/2 turns out. I have not made any other adjustments. The fuel is fresh, clean, and treated with Star-Tron. The oil is also new. There is no tach at the moment. It now starts right up and idles nicely.
Thoughts: I'm stumped. I took it out today and noticed better performance. It no longer misfires at idle or immediately cuts out when advanced to higher throttle. Today it would accelerate instantly, get on step, run well for about 30 seconds, and then start losing power or surging. I first attributed it to the linkage/throttle control on the old morse single lever throttle--but it high idles fine and the shifter is working as it should (albeit a bit stiff). I noticed that when I shifted to neutral after the surging, the longer it idled, the longer I could run normally at higher throttle (half, WOT) before it eventually started surging or lost power completely.
Additionally, when on ear muffs in the driveway, I can run it in gear at half-throttle with no surging or bogging. I've also noticed since running on the ear muffs that the tell-tale is noticeably weaker. Before running it in the driveway, it pissed like a horse, now, even after taking it out in the lake, it's more of a trickle. Suppose I ripped up the impeller using the muffs?
Thanks in advance for any thoughts on this.
Issue: The engine will idle easily but surges after about 30 seconds at anything above half-throttle. The longer it idles, the longer it will run at higher RPMs, but it will always lose power-- to the point where it almost shuts down at WOT. It will often "surge" revving up and down while in gear--without any adjustment to the throttle.
Background: This engine sat, fogged and shrink-wrapped, for about 5 years, until I starting working with it this year. Within the last month, I have replaced the fuel pump, fuel filter, water pump, and spark plugs. Compression is 110 in each cylinder. I also cleaned the carburetors and replaced most of the fuel hose. The carburetor adjustment screws are set 1 1/2 turns out. I have not made any other adjustments. The fuel is fresh, clean, and treated with Star-Tron. The oil is also new. There is no tach at the moment. It now starts right up and idles nicely.
Thoughts: I'm stumped. I took it out today and noticed better performance. It no longer misfires at idle or immediately cuts out when advanced to higher throttle. Today it would accelerate instantly, get on step, run well for about 30 seconds, and then start losing power or surging. I first attributed it to the linkage/throttle control on the old morse single lever throttle--but it high idles fine and the shifter is working as it should (albeit a bit stiff). I noticed that when I shifted to neutral after the surging, the longer it idled, the longer I could run normally at higher throttle (half, WOT) before it eventually started surging or lost power completely.
Additionally, when on ear muffs in the driveway, I can run it in gear at half-throttle with no surging or bogging. I've also noticed since running on the ear muffs that the tell-tale is noticeably weaker. Before running it in the driveway, it pissed like a horse, now, even after taking it out in the lake, it's more of a trickle. Suppose I ripped up the impeller using the muffs?
Thanks in advance for any thoughts on this.
