Surging / Bogging 25hp Merc

[Cordovakid]

Was in some shallow water, 1980 25hp merc, and the LU got into some sandy bottom. Like a fool, didn't think anything of it...about 5 minutes later, lost power, no water coming from pee hole and some white smoke. Shut 'er down ASAP....let it sit for a day...long story short, I got REAL lucky. No noticable problems for about a month after changing out the plugs, ran great, same as before. Then, one day, started acting like I was pushing the kill switch on the throttle handle off and on - not gradually losing power, but just dying quickly and then catching itself. Does it at almost all speed ranges, low and wide open. At full throttle, won't run top speed. I'm thinking fuel pump / carb jet issue, since it did overheat, and may have likely burnt some crap off the cylinder heads and got sucked into the jets / fuel pump. Just hoping it's not a timing / coil / stator issue. Anyone experience anything like this before? Pumping the fuel bulb didn't seem to make any difference...

 

[ondarvr]

Stuff can't burn off the heads and get stuck in the carb or fuel pump, it flows the other direction. If it cuts out like someone is flipping a switch, then it's more likely to be electrical. Check for spark on each cylinder with a timing light. Also check the compression.

 

[Cordovakid]

Well, that would be a good point to make...haha...think my brain got fried, not the cylinder....haha. Compression looked OK when I checked it - about 110 and 115 on each cylinder, same as before. I'll check the spark with a tester... Any specific way to check if it's a stator, coil or something else electrical? It's a pretty simple motor...Electrical makes sense, until you factor in that it won't run full wide open - bogs about 3/4 of the way.

 

[ondarvr]

Electrical components tend to fail as they heat up or are under more stress, which is what happens when the RPM's increase, so failing at higher RPM's is normal.
This doesn't mean the the carb is clean though, and cleaning it is simple.