Looking for help I have 1994 power quest 290 with twin 454 magnum efi motors. The starboard motor was running great and started having it over heat found old owner had stat in wrong place and a 195 in it. Removed stat and installed 160 in the stat housing along with replace the sea water impeller. Since then the motor has not run the same, when motor is started it runs fine for a min the idle starts to get alittle choppy and drops right under 600rpms, and u give any light throttle to motor it will spit and sputter and surge, but if you free rev motor it will rev right up to 2000rpms fine. I have done a compression test 1,6,7 came back at 140 and 2,3,4,5,8 came back at 150. I have changed spark plugs, and cleaned vst tank and screen. I put a fuel pressure gauge on the rail and when key is turned on psi will go to 10 and once motor is started and running will sit at around 28. Trying to see where to go from here

Which engine are we actually talking about here? Does it say 7.4 or 454 on it? And does it say EFI or MPI on it? It may sound like all the same thing, but it matters.

Does it look like this?

The one sticker has came off but the other motor says 454 magnun
mercruiser efi
crossram induction system
tried to upload picture but says I haven’t made enough post yet

DieselBoy,

Just spam this thread with "8", "7", etc, until you reach ten posts. this post away with your pics.

Thanks. Brad.

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