2008 150 VMAX

[bigfoot17]

So I’ve posted here in the last year a few times about my Yamaha V150TLR 2-stroke not reaching WOT most the times. Don’t really want to go through it all but I have done so many upgrades or replacements to it including anti-siphon valve, all gas lines, filters, cleaning and rebuilding carbs, fuel pumps, tried some new coils packs and spark plugs, even had it to a certified Yamaha mechanic that tested the stator, crank position sensor, timing, ECU, etc.

I bought this boat with a known problem late in the year 2021 for a fair price figuring I’ll throw some money at it. Well the summer of 2022 is when I had it in the shop for a few months. When I got it back it was better than it was before but stiff off.

The issue I was having was that the boat would only hit 4800-5000 rpm’s and a max speed of 46-47 mph. Every once in a while it would go to where it’s supposed to go to, 5600 rpm and about 57-58 mph. Last winter I had it out due to no ice on the lakes and it didn’t miss a beat when the water temp was cold then the issue seemed to come back when the water temps rose.

So this past summer I had the same issues again, ending start fines, accelerates no problem. As the engine is climbing up in rpm and speed there’s a point where it just cuts back and doesn’t want to go past 5000 rpm.

Here’s where I’m lost had it out yesterday and the water temps have cooled down considerably into the 40’s and the engine is running top notch again BUT ONLY in the cold environment. Does anybody have any ideas why this is???

***I am aware that engines run better when it cooler out but not this much of a difference***

[21XDC]

Fuel or spark.... I have seen when a propeller isn't lifting well enough and causes big speed differences. Like sometimes it gets enough bow lift to "pop" the bow up and gain 7-10 more mph and more rpms. But if it can't get to the "pop" stage it plows water at a much slower speed.

[rid 05 198]

Fuel or spark.... I have seen when a propeller isn't lifting well enough and causes big speed differences. Like sometimes it gets enough bow lift to "pop" the bow up and gain 7-10 more mph and more rpms. But if it can't get to the "pop" stage it plows water at a much slower speed.

What he says...

What boat and prop?

[bigfoot17]

2008 Stratos 285XL, 23 tempest plus prop

[cwilt]

Have you tried a lower pitch prop? 22 pitch maybe? See if you can get them RPMs back. Is the boat loaded with tackle? When I have 2 people and loaded with gear I am only getting 55 mph @5200 RPM. The smaller motors are very weight sensitive.

[bigfoot17]

Have you tried a lower pitch prop? 22 pitch maybe? See if you can get them RPMs back. Is the boat loaded with tackle? When I have 2 people and loaded with gear I am only getting 55 mph @5200 RPM. The smaller motors are very weight sensitive.

I have not tried a 22 pitch but willing to. The only thing I find odd is that ‘sometimes’ it does open up to 5600 rpm but most the times it doesn’t.

[Texas Rig]

Temperatures affect rubber expanding and contracting so it could possibly be a crimped vacuum line that when temps warm, the crimp closes more and opens up with lower temps. Check each chrome metal plate on top of the carbs, they have a rubber gasket under them and are prone to leak when not properly tightened.

[CJ1]

It is common in snowmobiles to chase a bad running one on top end and have it be the stator. They test fine but once warmed up will not supply correct power at higher rpms. Cj

[bigfoot17]

Temperatures affect rubber expanding and contracting so it could possibly be a crimped vacuum line that when temps warm, the crimp closes more and opens up with lower temps. Check each chrome metal plate on top of the carbs, they have a rubber gasket under them and are prone to leak when not properly tightened.

Thankyou for at least pointing out something else to look at. I know when I had it at the mechanic he tested out the stator.