200 hp yamaha planes in shallow water only

[skinsfan]

I have recently purchased a 21ft. center console with a 1991 200HP Yamaha. When in about 20 feet of water the boat will not plane out with WOT (only turning about 3300 rpm). When the boat is steered to shallow water (about 8 feet) the boat then planes out turning 4000rpm. I can then return to deeper water with the boat staying planed. Could someone explain this to me?

 

[JB]

Re: 200 hp yamaha planes in shallow water only

Sounds like you are badly overpropped, Fan.<br /><br />Even on plane, 4400rpm is badly lugging your engine. It should be turning 5500-6000rpm at WOT<br />How fast are you going (GPS)?<br /><br />Could also be that your engine is running on 4 or 5 cylinders.<br /><br />What has it done in the past?

 

[rodbolt]

Re: 200 hp yamaha planes in shallow water only

Hello<br /> I am with jb<br />your about 1500 rpm off anyway. the reason to plane in shallow water is due to the pressure wave. and that is about all planing is.<br /> anyway do a spark an compression test.<br /> have you ever seen the boat/motor/prop combo work correctly ?<br /> good luck and keep posting

 

[skinsfan]

Re: 200 hp yamaha planes in shallow water only

The prop size is 13 3/4 x 19-M. Does this sound like the proper prop size for this motor/boat? Thanks for your input!

 

[skinsfan]

Re: 200 hp yamaha planes in shallow water only

Compression looks good. 120-125psi on all cylinders. I pulled plug wires one at a time with motor running. Noticed change in idle speed on cylinders 1-4 but no change in idle speed on cylinders 5-6. I then pulled plugs 5&6 and noticed good spark (1/2" between plug and ground. Swapping plugs 5&6 with 3&4 made no difference. Charge coil reads good!

 

[rodbolt]

Re: 200 hp yamaha planes in shallow water only

hello<br /> what can I say?<br /> good spark, good compression. I would check for fuel.<br /> possibly a clogged carb<br /> good luck and keep posting

 

[JB]

Re: 200 hp yamaha planes in shallow water only

The carb that feeds #5 and #6 is gummed or otherwise not providing fuel.<br /><br />Might as well do them all.<br /><br />Good luck.

 

[skinsfan]

Re: 200 hp yamaha planes in shallow water only

Hey JB & Rodbolt,<br />It's amazing how much faster this boat runs when using all 3 carbs instead of just 2. You both hit the nail on the head! The bottom carb's bowl, main jet & main nozzle were gummed up (cleaned really well). The other 2 carbs looked good. I took it out for a test ride this afternoon. I came home with a big smile on my face! My wife might even let me come in from the dog house tonight. Thanks for the helpful hints and advice. You guys really know your stuff!

 

[rodbolt]

Re: 200 hp yamaha planes in shallow water only

hello<br /> thats cause JB been around a bit.<br /> glad your boat problem is solved. the wife problems are a tad more difficult good luck and keep posting