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Trying to diagnose why my 150 2 stroke maxes out at 4800 rpm at roughly 3/4 throttle. Beyond that, I get no increase in rpms. Not something that has just started happening, as it's been doing it for quite a few years. Over the seasons for various reasons, fuel pumps have been replaced, carbs overhauled several times by either myself or the marina mechanic, tested on external fuel tank, fuel lines and filters replaced, etc. But through it all, this has never improved or gotten worse.
It's on a 21' Parker sport cabin I bought new in 2004 so I'm sole owner and know the maintenance history. When we took delivery and trimmed it in flat calm conditions, it went to 5200 - 5400. So at least it did run faster rpm full range of the throttle at one point. But then again, everything was brandy new. Sweet spot typically 4200 - 4500 rpm so I rarely needed to max it out in the bay. That's why I didn't look too hard into the issue before. Figured whatever may be going on might continue to fail over time and finally be easier to find. But that just doesn't seem to be the case. Engine starts and idles great and at speed seems smooth and even. No surging or audible misses that anyone can tell.
According the the yam manual, WOT range for this engine is 4500 - 5500 rpm. So technically I'm in the range. But I'd like to get on the higher side if possible and get back that last 1/4 of throttle response.
Been through so many systems on the engine for various repairs over the years, I'm beginning to think the 14-1/4 x 16 prop may need tweaking. It's what's always been on the boat. But having never really had to do any prop testing myself, I'm not sure if too much pitch might cause a throttle dead spot situation like I've been having. So figured I'd post this hoping for some feedback from someone who's done it before.
So I guess my basic question is if a boat has a prop with too much pitch (lowering the max rpm), do carbs still react to the full range of the throttle to reach max rpm, or can the engine max out before reaching the throttle stop?
Any thoughts? Thanks
It's on a 21' Parker sport cabin I bought new in 2004 so I'm sole owner and know the maintenance history. When we took delivery and trimmed it in flat calm conditions, it went to 5200 - 5400. So at least it did run faster rpm full range of the throttle at one point. But then again, everything was brandy new. Sweet spot typically 4200 - 4500 rpm so I rarely needed to max it out in the bay. That's why I didn't look too hard into the issue before. Figured whatever may be going on might continue to fail over time and finally be easier to find. But that just doesn't seem to be the case. Engine starts and idles great and at speed seems smooth and even. No surging or audible misses that anyone can tell.
According the the yam manual, WOT range for this engine is 4500 - 5500 rpm. So technically I'm in the range. But I'd like to get on the higher side if possible and get back that last 1/4 of throttle response.
Been through so many systems on the engine for various repairs over the years, I'm beginning to think the 14-1/4 x 16 prop may need tweaking. It's what's always been on the boat. But having never really had to do any prop testing myself, I'm not sure if too much pitch might cause a throttle dead spot situation like I've been having. So figured I'd post this hoping for some feedback from someone who's done it before.
So I guess my basic question is if a boat has a prop with too much pitch (lowering the max rpm), do carbs still react to the full range of the throttle to reach max rpm, or can the engine max out before reaching the throttle stop?
Any thoughts? Thanks