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1GM10 won't run over ~2500rpm

1949 Views 8 Replies 6 Participants Last post by  cheoah
Here is what I know about the boat/engine:

-1gm10 w/410 hrs. Not sure of service history.
-boat sat from fall 2013 to May when I bought it.
-it had about 2/3 tank of diesel, I filled it in May and put fuel treatment in.
-I changed the oil, filter, tranny oil.

The engine starts and runs well, but won't rev over 2500rpm. It also surges a bit, at full throttle is remains at 2500rpm, and occasionally goes up to 3000 only to drop back down. Also, if I drop the revs, then 'gun' it, it will go above 2500 for a short time before dropping back.

I'm thinking some kind of fuel delivery problem....time to change the fuel filters? I drained the fuel filter today and fair bit of black particles came out....this also got air in the system so I know I have to bleed it next time.

Any advice/additional info. appreciated. Hoping it's not a big job!!!
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I had this exact problem on my old 1GM (not the 1GM10) and I changed EVERYTHING, reset timing, adjusted valves, checked compression, clean prop, nothing worked. Finally hired a mechanic who pointed an IR thermometer at the exhaust and told me it was a partially clogged. I dont remember if I fixed it before changing the engine for a 2GM13. I even borrowed a strobe light to check the speed of the flywheel to make sure the tach was reading right.
The 1GM was just too small for an 8000 lb boat cuz it had only 6.5 hp.
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