Yamaha 150 ('88)

[<Neal>]

No tell tale or water discharge when it started. Don't want to burn it up so I: 1) pulled the lower unit, installed impeller & kit + seals located just below 2) pulled thermostats - dealer suggested cutting them and reinstalling just rubber gromet = full open (replace if I start running in cold) 3) pulled lower popit/valve cleaned & replaced. I'm working in the drive way with a hose adaptor.

Still not tell tale or water discharge. Should there be????

Just bought this used 150 on an 18' Whaler. The motor sat unused for over a year. It turns over, even starts with full choke but wont "run". I need to be sure the cooling is OK before I run the engine.

[<Hamfisted>]

You need the thermostats in there and working properly. They provide some resistance that fills the entire powerhead with water needed to cool the top cylinders. With the thermostats removed there is no waterpressure resistance and the cooling water prematurely exits the powerhead without cooling the top cylinders, resulting in hot spots and premature wear on the pistons and cylinders. The standard temperature range is 120-130 degrees and you get an overheat warning at 140 degrees.
The problem with the tell-tale discharge is probably just mud or something else blocking the discharge tube or outlet. Use a piece of stainless wire to ream out the opening while the motor is running on the garden hose. When you flush on the hose make sure you use the muffs that feed from both sides. The type that use a Y-pipe to feed each muff. There's a dividing wall behind the plastic inlet covers and the inlet needs to be fed from both sides to ensure enough water volume reaches the waterpump.
If it sat for a year without being run you need to pull the idle and main jets out of the carbs and give them a good cleaning with some Berryman's Chemtool spray (Walmart). Spray up into the carb bowls through the jet openings and clean out the bowls too. If you don't have one already go to www.YamahaPubs.com and order yourself a factory service manual for your motor. It will have all the important imformation and specs needed to properly maintain you motor. The carb jets are those brass bolt looking things on the lower sides of each carb bowl. Take the air box off so you can access each one. Be careful when you reinstall them because they're only brass, and the carb is only aluminum. Inspect the O-ring seal on each main jet and replace it if its torn, cracked or distorted ($5 each at the dealer...). The pre-'96 carbed Yamahas are very susceptable to gum and varnish buildups in the jets. After '96 Yamaha remodeled the carb and raised the jets to try and eliminate this problem. Whenever the motor won't run unless you "choke" it there's a strong probability that the idle jets are clogged up. Get the service manual soon as you can.


Mike...... Miami, FL

[<Neal>]

Thanks. Your suggestions seam solid and well thought out.

This seams like a reputable Yamaha dealer. More than a couple of their staff thought cutting the thermostat was a good idea. they said the rubber gromet would provide enough resistance to keep the pressure up.

I have cleaned the tell-tale discharge. It is clear. Thanks for suggesting the Y type of hose adaptor. I am using that type.

I will clean out the gum and varnish from the carbs et al.

[<Hamfisted>]

No, the rubber grommet left behind won't do anything, except maybe collapse and get lodged in the water jacket somewhere, causing new problems. The guys that designed these motors were a bit smarter than the techs that turn wrenches in the back of the local dealerships. The thermostats need to be there and in good working order. Use new gaskets when installing them and torque the bolts evenly and to specs with a torque wrench. The thermostats control waterflow and ensure the cylinders get covered in cooling water and maintained within a specific temperature range, cooled evenly with no hot spots (blown head gaskets...). So unless those tech reps are offering you a free powerhead replacement I wouldn't listen to 'em.


Mike ....... Miami, FL

[<Neal>]

I hear what you are saying...... But it sounded so good, so easy. I will probably go ahead and purchase the thermostats. Better safe than sorry.

[<Neal>]

I almost forgot. I worked on the carborators as you suggested and they were very fouled. That may be the solution to my idle/choke problem. Thanks so much.