www.iFourWinns.com

Just bought 1990 180 with cobra 5.0 and cobra 4.3 outdrive. At WOT getting 4400 rpm which matches sticker on Motor but only running 30mph instead of 50 mph like manual states. Has 19 pitch prop.

If you do in fact have a 5.0 engine and a 4.3 drive, then your drive ratio is not right for the engine, it will give faster accel on plane but lower top speed.

Verify the accuracy of the tach and the speedo. If its a water pressure speedo it might be off by a bit. If its GPS speed (accurate) then you need to look at tune up issues, ignition/fuel. When was the last tune up? Your engine is pulling the specified rpm but not making enough power to move the boat fast if your speed is accurate.
Given the difference in drive ratios, it should be able to pull a 21" pitch prop, if in better tune.

My H-200 (more than 2' longer) with the same engine, will be running at about 25 mph @ 3200 rpm. I have not tried WOT yet as the water here has been too rough all season, but based on past results my top end was in high 30's low 40's. Boat needs a bigger motor lol.

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88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

Used GPS to verify mph, so that is correct. Trying full tune up to look for something obvious. Even with the 19 pitch prop it's a dog on the hole shot. Something not right but it feels like Motor running smooth.