1978 175 merc no plane

**crappiehuntr** · 09-09-2023, 07:05 PM

I bought a 78 175hp and it doesn't want to go on plane it's a
22' bay boat. Previous owner replaced the stator its all new along with boxes ,Compression is between 110 and 115, has stronger spark than any outboard than I've ever seen checked every single plug and coil. Starts easy and revs good on warm up lever. Have not timed it or cleaned carbs. It doesn't starve or run out of fuel if you keep the power on trying to get on plane I droppped pitch on prop way down. Any ideas thanks!

**crappiehuntr** · 09-09-2023, 08:03 PM

I forgot to mention added an electric fuel pump and also ran throttle at engine by hand no difference

**rhardwick** · 09-10-2023, 10:30 AM

Check timing under a load. Pull the cover off the carbs and using your timing light see if the fuel is spraying out of the nozzles. You do have a big difference on compression, 110-150 psi. Check it again with the engine warm.
I think that engine had a idle stabilizer or high speed timing advance module (maybe only the 200 hp), someone will correct me if I'm wrong. That module can be disconnected if faulty.

**pcrussell50** · 09-10-2023, 12:05 PM

Originally Posted by rhardwick

Check timing under a load. Pull the cover off the carbs and using your timing light see if the fuel is spraying out of the nozzles. You do have a big difference on compression, 110-150 psi. Check it again with the engine warm.
I think that engine had a idle stabilizer or high speed timing advance module (maybe only the 200 hp), someone will correct me if I'm wrong. That module can be disconnected if faulty.

The 2.0/150’s had idle and oil modules too. (Ask me how I know). On both my 2.0/150 and 2.4/200 I have removed all modules and using premix.

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Agree the OP’s problem is acting like he’s not getting timing advance when he needs it. I have a Yamaha that has a very stiff trigger arm. It’s finally loosening up but at first it was so stiff that the timing would stay retarded against safety spring in the timing arm and would not go on plane either. Or else it would explode up onto plane suddenly as the stiff arm finally moved.

I doubt the OP has as stiff trigger problem, but his symptoms definitely sound like he’s not getting timing when he needs it.

-Peter