S150TXRU won’t rev past 4200

[JerEazy2]

How about a very simple, no cost check and see if the throttle is indeed opening fully? will take about 5 mins to do, without engine running of course!

absolutely on that one. Will look down the beasts throat once the air box is off.

[JerEazy2]

duplicate - sorry

[JerEazy2]

Ok - so we saw in my other thread that I rebuilt the carbs - but it didn’t help my RPM issue.

I still intend to run a spark check and re-do the compression test (I don’t remember the numbers, but they were all near each other)

but it in my research I saw that this boat generally came from the factory with a 200hp. I actually can’t find one with a 150 on it - smallest is a 175. So that leads me to believe that the previous owner repowered at some point and skimped out. Or skimped our at build time. He only used it as an island commuter, so it’s possible it never bothered him or he just didn’t care. It’s just a thought. This might explain the RPM issue as the 150 just can’t quite do it.

now, today I noted at 3500 RPMs I’m doing 29mph on GPS. So the speed is there. So in true Eazy fashion I picked up a 14/14 3 blade off of eBay that should be delivered next week. All things being equal this should get me up to about 4500-4700 RPMs.

Not the top top end of the WOT range, but in spec. More to follow.

[TownsendsFJR1300]

Are the throttle butterflies opening FULLY??

As you noted, once the throttle is opened fully, you can usually hear MORE AIR going thru the engine...

Yours doesn't sound like it's opening fully..

[JerEazy2]

Are the throttle butterflies opening FULLY??

As you noted, once the throttle is opened fully, you can usually hear MORE AIR going thru the engine...

Yours doesn't sound like it's opening fully..

My understanding of fully opened throttles on a carb means they are flat - which mine are at WOT. I’m starting to think that the 150 just can’t spin a 15.25 prop and push that much weight....

I really over-troubleshot. I should have left the original 13.75x17 on there and checked what the RPMs went to after the bottom cleaning and carb job compared to the 4200 on the test run. I say that because on the test run it got to that 4200 on a load of 4 adults and a child. My dumbass didn’t bring it with me today so I couldn’t swap out.

Anyway - it’s all conjecture until I can do a bit more testing. I’ll check spark and compression tomorrow and hopefully test run either the old 17m or new 14x14 next week.

today I’m too worn out and too beer’d up to do any more work

[JerEazy2]

Sorry for duplicate - but wanted to keep the posts relevant.

compression test this morning showed (first 3 starbd next 3 port)
110,109,105, 110, 110, 107

it was a quick and sloppy check (cold with throttle plates closed) with The Admiral turning the key.

spark is definitely occurring based on inline test light and that wonderful feeling in my hand when removing a spark plug wire from a running engine. Interesting occurrence though. When pulling the plug wire from the bottom cyls and especially the stbd bottom (6?) the engine almost dies completely. The rest there is a mild stumble.

new prop arrives Thursday but in the meantime I put my 13.75x17 back on as it did have the highest RPM results prior to fiddling.

[99yam40]

I would worry that all plugs when pulled while idling did not cause the same results.
I know on some injected motors they do not run n all cylinders in neutral while idling, but I am sure you carbed motor should be hitting on all cylinders all of the time

[panasonic]

I agree with Yammi. Have you checked all things like plug caps for good connections and arcing. Spray a light mist of water on the plugs wires at night and see if they light up..

And did you ever check the timing?? Since you are presumably the second owner god knows who was screwing with what before you got your hands on it.

[rodbolt17]

now would be a good time to find a shop with test wheel YB-1626, that 150 should spin it at 4600-4800 RPM, the IDC dyno should be 2900 PSI at 5000 RPM.
if it cant then fix the motor.
if it can fix the hull/rigging issues.
never seen a plug wire fail on a Yamaha. some occasional resistor caps.
myself before I got to far in to splatter gun mode I would run a simple test with YB-1626.
may save a lot of time hunting wabbits and chasing ghosties long before a wristpin lets go.

[JerEazy2]

I agree with Yammi. Have you checked all things like plug caps for good connections and arcing. Spray a light mist of water on the plugs wires at night and see if they light up..

And did you ever check the timing?? Since you are presumably the second owner god knows who was screwing with what before you got your hands on it.

I have not checked the timing as I frankly am not sure how.

and the plug wires were pretty nasty so I was planning a replacement anyway. Guess now I can rationalize it!

[99yam40]

have you ever used a timing light on one of your cars/trucks?
Same use on checking timing on an outboard

[JerEazy2]

now would be a good time to find a shop with test wheel YB-1626, that 150 should spin it at 4600-4800 RPM, the IDC dyno should be 2900 PSI at 5000 RPM.
if it cant then fix the motor.
if it can fix the hull/rigging issues.
never seen a plug wire fail on a Yamaha. some occasional resistor caps.
myself before I got to far in to splatter gun mode I would run a simple test with YB-1626.
may save a lot of time hunting wabbits and chasing ghosties long before a wristpin lets go.

This is why you’re the man.

I’ll say with confidence that most mechanics in this area have a minimum service charge. And I got the 14x14 for less than that. So if it solves the problem then win. If not, it’ll go back on E-Bay.

Part of of me is even curious if the tech is accurate. I say that because with my current 15.25x15 4 blade I can confirm 29mph on the GPS when the tach was saying is 3500. Welp, punch that into a prop slip calc and that’s a negative 9 prop slip... Negative slip is of course impossible. How much of a punch in the face would it be if that was the problem?

had to finish some tile and yard work today. So no extra work or checks. More to follow this week/weekend

[JerEazy2]

have you ever used a timing light on one of your cars/trucks?
Same use on checking timing on an outboard

Oh - I never really looked into it. Thought it would be more in depth than that. But truth be told, no I never have haha.

Used to set the timing by sound and feel and trial and error. But we also back then couldn’t afford a timing light LoL.

[walleye1]

Run it at wot with the air box off and have your buddy squrt gas oil mix in each venturi to see if it picks up rpm.
If not it is a prop isue. No dealer in my area will stock a tes wheel.

[rodbolt17]

that gas trick will only work if it is a fuel issue.
timing setting on an outboard of that era is NOTHING like setting it on an old chebby wid da points.
never saw an old chebby that I had to check at WOT.
remember you have idle timing,carb pick up timing and timing at WOT.
I would make some calls for a shop that has either the test wheel or a dyno before I blew a wristpin bearing.