seahorse

just for the sake of discussion, have you looked at other brands of outboards for your boat? Here is a link to a recent video of an accurate comparison between the brand new Merc 150 and the established Evinrude E-TEC 150

A 1990 powerhead is a different block design than your original '98 powerhead. OMC redesigned the big block 3.0L engines in 1993 and improved other items and introduced them as the Ocean Pro and Ocean Runner models. Have an experienced tech check over your powerhead to see if it was a jury-rigged replacement or if it is not what was represented to you.

Was a new oil pump installed with the crankshaft sleeve installation or at least were the pump's oil seals and o-rings replaced at the same time? If not, then the corrosion on the crankshaft which caused the leak in the first place, probably damaged the oil pump seals and that may be why the engine is still leaking oil.

Many of them have an L stamped on the end of the propshaft

When you add an additional gauge to the fuel sender wiring, you are changing the "load" and resistance on the circuit so the gauges will either not be accurate or not be operational.

possible air leak in the intake hose connection?

There is an air motor diaphragm and a fuel pump diaphragm, various flapper and check valves plus an oil piston pump and the alarm electronics. There are pressure tests that can be done plus flow tests, alarm tests, and priming tests, all in the service manual. This may help and it has a great picture of the insides of the pump: http://continuouswave.com/whaler/reference/VRO.html

How did the other diaphragm look?

On how many websites have you posted the same question and images? There is an oring under the cover of that plus a needle valve and float. Use the service manual procedure for setting the float level after replacing the valve and cleaning out the fuel cavity.

A sharp trained tech can fix you up using your original harness and just adding the engine drop cable, boat network, and digital gauge(s)

Talk to some authorized dealers. They can check the factory parts database to see if other dealers have them in stock, plus there was a bulletin about replacing ones that fogged over from some years ago. I believe, but not sure, that they were made by Faria Gauges and you might contact them.

If you were using the round ear muffs, that may have been your problem. The rectangular ear muffs have a better fit over the Yamaha inlet screens. You should also use a dual feed flusher for best results. The hose on the motor with the garden hose fitting is NOT for running the motor. It is only to have water fill the block and wash it out. Read the owers manual - do not use that hose and run the motor.

Besides all new cables, controls, gauges, and wiring, you may have to fill the transom mounting holes and redrill them farther apart to fit the Yamaha motors. Likely your engines are at 26" centers and Yamaha V6's need about 27 1/2" centers to clear each other. That may also put a bind on the rigging cable on the stb. engine if it hits the edge of the end of the transom. Measure carefully before committing to the motors.

That article is exactly why the outboard and oil companies got together and "designed" the NMMA FC-W oil certification protocol for 4-stroke outboards. Modern car oils have lower anti-wear additive protection due to the EPA's concern about wanting catalytic converter effective life to be longer.

The first thing to do is get rid of the battery wing nuts and use stainless steel nuts and lockwashers tightened with a wrench. Then check the battery cable fastening at the motor. Your motor stumbling when trimming is due to lack of voltage to the ignition and electric fuel pump and injectors. Somewhere in the electrical system is a "restriction" or your batteries are weak. Yamaha does not recommend the use of maintenance free or sealed batteries. In very rare instances, the stator could be weak or the regulator acting up.

Yamaha requires the dealer to personally sign a serial numbered pre-delivery form, as well as the buyer, to state that he has run the motor and set it up per the Yamaha recommendations. It is a requirement for warranty registration. Yamaha dealers are also not allowed to sell the motors in a box and have the customer install them. How are you going to get your motor registered for warranty if you are doing the rigging and setup? Yamaha does publish a complete "how to" rigging manual that you can order from a dealer.

thanks, Wiley, the forum is back to being easily readable again.

the dark looking plug could be a leaky injector. Because of your sluggishness, connect a fuel pressure gauge to the diaphragm lift pump and also to the fuel rail test port and run the motor at all speeds while monitoring for any low or erratic pressure indications. Also check for a significant pressure leakdown after turning the motor off which would signify a leaking injector or a bad pressure regulator. Hooking up a piece of clear fuel line to lift pump inlet will indicate if there are any air leaks in the boat's fuel system which could also cause a lack of power. It's best to have a service manual handy plus an understanding of the motor's EFI system.

Not enthused about the new color scheme - the blue on blue print is almost impossible to read with my old eyes. Can you go back to the original colors or try a combination that is easier on the eyes? Thanks

Have the thermostats in the motor been tested for proper opening temperature? You cannot troubleshoot an overheating problem by using the hose fitting or a flusher muff. As you said, wait until the boat is in the water and floating.

How do you feel about 4-strokes having to drain dirty hot oil into a bucket, changing out an oil filter, catching any drippage, pouring 5 to 8 quarts of oil at the top of the motor, then cleaning everything up and taking the old oil to a recycling center? With an E-TEC and the optional 3 gal. tank you don't have to do much, and you keep your hands clean. The best part it takes only a moment or two compared to a 4-stroke oil and filter change.

You would be a lot happier with the 200HO-225-250 90° block. They have so much more torque in the midrange than the 60° motor and will make running in a following sea a lot nicer, especially when you are loaded down with fuel, ice, people, and gear.

The low oil alarm is triggered by a float inside the oil tank. If it is sticking or shorted you will get a 10 second warning horn sound and the LOW OIL light will come on and stay on as long as the float is stuck or the electrical short remains. Disconnecting the oil tank wiring at the motor will tell you if there is a bad gauge or a bad float. Any crack in a fuel component is an indication to replace that part. Your fuel feed problem could be any number of things from the pump, pulse hose, fittings, restrictions, boat fuel system problems, etc. Each has to be checked out or substituted to find the problem(s).

Don't overlook the oil filter inside the motor cover. Be sure to note the arrow direction before removing it as I think your engine is supposed to have the arrow facing away from the motor, not towards it.

If it comes on again, run the self-winterizing program as that may remove an errant air bubble that can trigger false alarms. If that doesn't fix it, it's time for factory-trained professional help. Be sure to check all your connections and oil hose for any looseness, leaks, kinks, etc.