200 hp Yamaha water flow

Mudd_catt · #1 August 29th, 2005, 03:19 PM

I have a 200hp 88 model Yamaha that I have had about a month now, and just started having problems (I think) with the water flow through the motor. When I first got it, the tell-tale was very strong and the pressure gauge would rise to about 12 or 14 at idle, and when rpms were raised, the stream would get even stronger, and the gauge would go up to about 18-20. After a trip at WOT testing the boat (and my handling skills) the tell-tale has a weak stream, and the gauge barely moves at idle, and at raised rpms, the stream gets a "little" stronger and the gauge rises to about 6 or 8.

I suspected a weak water pump, so I changed it. No change in conditions. I tried "backflushing" through the (what I think) the check valve to the motor, both directions, with the foot off. no change. After I put the foot back on, I took the fitting on top of the motor that the gauge tube fits to out, and the only way that I could get water to come out was to raise to a around 2500 rpm. Even then it wasn't a steady stream, it just kinda "spurted" out. I even tried running with the left thermostat and cover completely out of the motor for a few seconds, and no water came out then either. Running the motor with the check valve off the motor produced the same results, no water unless at higher rpm.

Have I got a blockage? or something that I have missed. I have searched the forum till I got crosseyed, and tried all that I could find. Also, keep in mind that there has been NO saltwater NEAR this motor as far back as 5 years ago, and I suspect, never.

rodbolt · #2 August 29th, 2005, 03:55 PM

ya need a service manual. at least that way everyone knows what part is being disscused. the pressure valve and grommet usually is the culprit. at low speeds it bleeds off all the water pressure and the block wont fill if it leaks or is removed.

Mudd_catt · #3 August 29th, 2005, 04:12 PM

I am in the process of trying to find a service manual locally.

I assume the pressure valve and grommet is what I called a check valve on my old johnson, located at the rear bottom of the block, with a 3/4 in hose going around to the side of the motor?

rodbolt · #4 August 29th, 2005, 04:41 PM

its on the exaust housing on the lower stbd side. even on your johnson they were called pressure control valves. but on a yamaha the water flow is such that if it leaks it will dump pressure and water directly back overboard and never fill the block.