Best New 4-stroke engine (150 hp)

[Psalm 99]

I'm ready to give up on my Yamaha 150 hp 2-stroke. Engine only has 619 hrs but has failed continually over the last 3.5 years. Just about everyone around here has a Yamaha 4-stroke so I'd like to go that route also. This will be have a 25" lower unit. Before I take the plunge, could you guys give me your opinions on the model of Yamaha 4-stroke I should get. I so sick of my engine failing that reliability is the key issue. I know Yamaha makes a great engine. I bought mine with boat on E-bay about 3.5 years ago and its pretty apparent that the original owner also had problems. Thru this site I've worked on the engine and replaced just about everything I that could be causing the problem. Last two items were a new CDI unit and Pulsar coil. In a nutshell: fuel lines and filters are new, fuel pumps have been replaced twice, spark plugs are new, all thermostats, temperature sensors (3) and oil level sensor are good, helm alarm works, carbs have been taken apart numerous times and fully cleaned with new floats. On muffs, stator output is 200 V, all coils output correctly, been through the entire Mechanics Manual and all is good. The next thing would be wiring harness but I'm tired of wasting money on parts. Winky Blink shows no errors. Engine will run for hours on muffs and about 10 minutes after leaving dock. Then the rpm's will collapse immediately down to 1600 rpm where the engine will run very smoothly but will not respond to the throttle about 1600. If I let just cruise at ths speed for a couple of hours but with the throttle set at a higher rpm (3200), the engine may explode upward (very fast) in rpms for a few seconds or may just take off and run beautifully at the 3200 rpm setting for maybe few minutes of as long as 10 minutes (time to dock). A new engine is a lot of money but, at 71, I've like to spend the time left with a reliable engine.

[boscoe99]

They don't get any more reliable that the standard F150.

You can't take your money with you, and you won't be leaving it to me, so I say go ahead and buy the new motor.

[zenoahphobic]

I think I know how you feel, you have given up.

But from what you say the engine has never been right all the time you have owned it, so you don't know that it actually can run right. But 600hrs plus suggests it was not always a lemon.

Having said that, you have done a lot to it so it seems there is nothing left to renew, two strokes are simple and you say it does run right for awhile.

It therefore seems obvious you have a fuel problem and/or ignition but you changed the CDI. So this suggests very much a carby et al thorough inspection. But it would be a waste if the fault is because of a loose wire or something simple (cheap).

I don't believe in lemons per se, and multiple faults are rare. They can be created by intentionally (fiddling with stuff that has nothing to do with the fault and not understanding the consequences) and unintentional trying to "fix it" situations though. Normally an engine problem usually arises out of one fault that makes the engine not run.

And I am not sure that a total engine replacement will fix your problem as there is still the boat eg. Wiring, tank ,fuel lines and resident gremlins.

After those words of wisdom, I to interested what might be "best new engine" but of higher HP. I am worried about the massive maintenance commitment to a four stroke as unlike youI have had decades of cost free and trouble free Two stroking!

[pstephens46]

I can vouch for the F150. Bought used and zero engine issues for six years. Boat wiring suspect but engine nothing...is the 150 four stroke the maximum hp for the boat? Could you go higher?

[panasonic]

Go for the new F150 and get some worry free boating on the clock. Sorry you couldn't find the problem with the one you have..that is disappointing to hear.

[Psalm 99]

Thanks guys. Looks like the F150 will be the engine. Local Yamaha shop gave me a rough estimate of $14,000 for the engine and about $2,400 to install it. Seems reasonable. I'd sure rather fix the 2-stroke but enough is enough. When it runs right, its a thing of beauty. Then like a switch it crashes down to 1600 rpm where it purrs but will not respond to the throttle. I can almost take the carbs apart in my sleep and the fuel supply to each carb is real clean. I've got a couple of months before the local Yamaha shop can install the new engine so I may take the carbs apart and put them thru my good sonic cleaner again plus maybe put new fuel pumps in (again) as they are cheap but I've been down this road a number of times with no success. Whatever is causing this problem its something small but real aggravating.

[pstephens46]

You will love it!

maybe you can get a little cash for the old engine?

[boscoe99]

Once you have the four stroke installed you will wonder why you waited so long. You will then realize why four strokes have become so popular.

Remember, there are two types of four stroke owners. Those that have tried to start it when it is already running and those that will try and start it when it is already running.

Try to remember to turn it off before pulling the boat out of the water.

[zenoahphobic]

Thanks guys. Looks like the F150 will be the engine. Local Yamaha shop gave me a rough estimate of $14,000 for the engine and about $2,400 to install it. Seems reasonable. I'd sure rather fix the 2-stroke but enough is enough. When it runs right, its a thing of beauty. Then like a switch it crashes down to 1600 rpm where it purrs but will not respond to the throttle. I can almost take the carbs apart in my sleep and the fuel supply to each carb is real clean. I've got a couple of months before the local Yamaha shop can install the new engine so I may take the carbs apart and put them thru my good sonic cleaner again plus maybe put new fuel pumps in (again) as they are cheap but I've been down this road a number of times with no success. Whatever is causing this problem its something small but real aggravating.

You have to take a fresh look at this and take another approach. You agree it is something small. "Doing something in your sleep" already says you must go at this differently, simply you have forgotten or missed something.

When you have had a good sleep, good feed and plenty of fresh air and a clear relaxed mind, do it differently and slowly as if this is new.

You may just want to study the manual, it's diagrams. If you want just look over your engine with good light. What you do first is the opposite of previous. If you get tired rest take a break and don't in any way feel pressured or even expect success. If you had missed something it is this approach that will uncover something. It is also surprising how something can show up when you have already resolved to buy a new engine and therefore you are getting rid of this one anyway.

Not quite meaning to be the psychologist, but a change in attitude helps greatly. There are many many examples. For instance how have you frantically looked for your keys,wallet, spanner, whatever and anger takes over, only to find them incidentally the next morning doing something else right there in front of you.

[Psalm 99]

It is sort of a crime to trash an engine having only 600+ hr. Especially as this engine is super clean and runs strong and quiet until the problem occurs. Its run good for a number of trips and then the problem surfaces. Lately, I can only run for about 5-10 minutes before it happens. Pretty sure its electronic as I've seen a fouled carb a couple of times: engine vibration goes up as well as a loss of power. OK, I've taken a few deep breaths and have calmed down although I do regret the rather large dent in my helm where I smashed my head in frustration (attempt at humor). I've got those two months before the shop can install the new engine and will continue to tinker with it. Process would be sort of fun if I could make progress.

[zenoahphobic]

It is sort of a crime to trash an engine having only 600+ hr. Especially as this engine is super clean and runs strong and quiet until the problem occurs. Its run good for a number of trips and then the problem surfaces. Lately, I can only run for about 5-10 minutes before it happens. Pretty sure its electronic as I've seen a fouled carb a couple of times: engine vibration goes up as well as a loss of power. OK, I've taken a few deep breaths and have calmed down although I do regret the rather large dent in my helm where I smashed my head in frustration (attempt at humor). I've got those two months before the shop can install the new engine and will continue to tinker with it. Process would be sort of fun if I could make progress.

I thought there was a lot of shuffling between the relationship between fuel and electrics. Although said before that 1600rpm sounds like the limp mode enforced by overheating, but not overheating so engine thinks overheating. Have another go at that wire from CDI to earth and everywhere the thermoswitches and oil level switches go as inputs to CDI (explored before I think.) Sounds "electronic" like just a small signal causing the clear changes.

[Psalm 99]

Just re-checked the oil level sensor riser. Right at spec. Thermoswitches were also exact spec when checked. I think overheat or low oil will give an alarm at the helm and, although the alarm checks out ok, there is no alarm when this occurs. Once before when this happened, I cleaned all the grounds which seemed to solve the problem for a while so this is the first thing I did once the problem came back. I do disassemble the ground, emery cloth the fitting, spray with CRC, and re-assemble. Still, I might have botched one and I'll do them over tomorrow. Sure appreciate the help!

[Jason2tpa]

Engine will run for hours on muffs and about 10 minutes after leaving dock. Then the rpm's will collapse immediately down to 1600 rpm where the engine will run very smoothly but will not respond to the throttle about 1600. If I let just cruise at ths speed for a couple of hours but with the throttle set at a higher rpm (3200), the engine may explode upward (very fast) in rpms for a few seconds or may just take off and run beautifully at the 3200 rpm setting for maybe few minutes of as long as 10 minutes (time to dock). A new engine is a lot of money but, at 71, I've like to spend the time left with a reliable engine.

Very few would dispute the quality, reliability, and long term durability of Yam 2 strokes. The key to experiencing these qualities rely primarily on preventative maintanance. Unfortunately, despite your best efforts with PM, it sounds like the previous owner did not share the same beliefs...or perhaps just didn't care. I understand your wanting to give up on the engine, especially if you've dumped $$$ into it without getting consistent results. But before you drop 14k to replace the engine, have you considered replacing main components affiliated to the issues you're experiencing?

The issue you described above indicates it's carb related, especially since you've replaced just about every other fuel system component. Yes, you've pulled and cleaned the carbs numerous times, replaced floats. How about the jets? Are you pulling each jet (I believe 6/carb for your engine) and cleaning so thoroughly that you can hold each jet up into a light source and see through the jet. If you haven't done this....there's the cause of your current issue.

If you have pulled jets each time you've cleaned carbs, perhaps there is something else that's being missed or something else malfunctioning with the carbs. So how about replacing the carbs? Replace one first, then retest engine. If same result, replace 2nd carb. Just guessing here, but each carb new probably costs $350-$450. So total cost of replacing carbs with 2 new ones would be around $900. Sounds a heck of a lot better than 14k. If the powerhead is in good shape, electronics are in good shape, LU is in good shape....if you get the fuel system to properly function then it sounds like your engine would perform great.

[99yam40]

having gauges that will tell you if an overheat or low oil alarm is setting comes in handy.
you need to test the alarms and see if they set the alarm and indicate as they should when they come in
guessing is not the way to go

[Jason2tpa]

Engine will run for hours on muffs and about 10 minutes after leaving dock the rpm's will collapse immediately down to 1600 rpm where the engine will run very smoothly but will not respond to the throttle about 1600. If I let just cruise at ths speed for a couple of hours but with the throttle set at a higher rpm (3200), the engine may explode upward (very fast) in rpms for a few seconds or may just take off and run beautifully at the 3200 rpm setting for maybe few minutes of as long as 10 minutes (time to dock).

After reading your description above a bit closer, I may need to change the content of my previous post, regarding the issue being carb related. Reason being, what your describing sounds temp related (or temp alarm related).

Sooo, the engine runs normal at the low end of normal operating temp (muffs and while just underway). Then as you've run the engine for 10min after leaving the dock at rpms above 3k, the engine temp should rise and remain at the higher end of normal operating temp....but perhaps it's not. Perhaps it's rising above normal temp, and thus overheating...

* the high temp alarm triggers limp mode, yet you're not given audible or visual indicators this alarm has triggered....

* the engine rpms abruptly drop below 2k (limp mode) until the temp lowers into the normal operating temp range....

* you having moved the throttle lever forward during this "cool down" time, once the engine temp lowers enough so the thermosensors don't ground, the engine responds abruptly with hp to reflect throttle position...

* and then your off and running again above 3k, until the engine temp rises above normal operating temp, yet again.