Low rpms on 2016 242 lse

[Pinhacker71]

I’ve had this boat for close to 2 years. Able to get to 50 mph when I first got the boat but it always seemed to struggle to get there. Out on lake this week and noticed starboard engine 7350 rpms max and port 7450 max. Last 1/4 of throttle doesn’t do anything. Changed plugs at beginning of season and did oil change. No oil in air filter and oil level is good. I did ribbon delete last season with no noticeable improvement in rpms. I didn’t place the spacers after I removed ribbons. 45 mph max with 5 passengers and 1/2 tank.

 

[haknslash]

Check your throttle cable adjustments and make sure you're hitting the stopper.

 

[Pinhacker71]

Electronic throttles. Don’t know how to do this. I’m not sure it can be done with e throttles.

 

[seadude]

The e-series bimini is quite a parachute at high speeds- mine struggles to reach 50 also and even less when loaded or sub optimal conditions.
Took her out topless last week for a shakedown cruise, saw 52 with the wind!

 

[swatski]

45 mph max with 5 passengers and 1/2 tank.

This is not bad at all, if running with bimini up, a bit of elevation (?), and hot weather (?) is a speed killer - especially w/humidity.

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[J-RAD]

I seem to be missing RPM's this season in my '16 AR240 too... I'm not sure what's going on. Changed oil and plugs at the beginning of the season using the Yamaha kits. Oil levels are where they should be, APS is adjusted the stops, plugs are gapped to spec and look fine, fresh gas, clean hull, impellers are pristine and clear of debris... ribbon delete from day 1. Running on home waters (4500ft el.) In standard conditions but I'm only getting to 6,500 RPM and struggling to hit 40mph which is down 5-7mph. Seems to be both engines.

I really don't want to take it to the dealer if I avoid it, but I'm at a loss? The engines seem to perform normally otherwise... just not reaching the top end. I've been charging the batteries to see if that has an effect (were reading 12.3V). If that doesn't work I'll unplug my Ridesteady to see if that's somehow affecting it. Beyond that...?

 

[Gym]

@J-RAD. You said standard conditions at 4500 feet elevation. If the temp was only 70F on a dry day your engines were breathing air as if they were operating at 11857 feet above sea level. I suspect your air temp was much warmer than 70F making your density altitude much higher.

If only one engine had this issue I would look at an engine issue. With both engines doing the same thing, whereas you're properly tuned I would consider density altitude (thin air) as the culprit. Pilots have to deal with this on each take off and landing.

To prove this trailer your boat to a location much lower than your 4500 feet. If it runs normally you've found your answere. That would be a much cheaper and less stressful way to address the problem.

 

[J-RAD]

Thanks for your input @Gym. I understand your theory, these engines do suffer at altitude. I'm just having a hard time rationalizing it against the previous 2 seasons on the same waters in similar to identical conditions. I've never struggled to reach 40mph like I am now and it's been consistent the 5 times I've been out. Temps have varied from mid 70's to low 90's, very low humidity. I'm hoping I can speak to another yamaha owner on my lake with 1.8s and see what they're experiencing.

 

[Gym]

@J-RAD. You initially mentioned low RPM. That's what I was addressing. Low speed can be caused by other issues. While low RPM will cause low speed. You can also have full RPM with low speed. Your load, hull growth, rough water conditions and winds will affect speed but not RPMs.

Again, If you have access to a lake around 1000 feet or lower you may easily solve this dilemma. You mentioned some of your boating trips were in the low 90s. That would give you a density altitude of 13016 feet above sea level. I'd have a hard time breathing with air that thin let alone my boat. The only mechanical fix I can think of is a ram air scoop to force more air into the engines. I think a trial run at a lower altitude would be easier.

 

[J-RAD]

@J-RAD. You initially mentioned low RPM. That's what I was addressing. Low speed can be caused by other issues. While low RPM will cause low speed. You can also have full RPM with low speed. Your load, hull growth, rough water conditions and winds will affect speed but not RPMs.

Again, If you have access to a lake around 1000 feet or lower you may easily solve this dilemma. You mentioned some of your boating trips were in the low 90s. That would give you a density altitude of 13016 feet above sea level. I'd have a hard time breathing with air that thin let alone my boat. The only mechanical fix I can think of is a ram air scoop to force more air into the engines. I think a trial run at a lower altitude would be easier.

Clean hull, calm air and waters, no cavitation. Just can't rationalize the difference season to season. I don't think there's a lake in the state of Utah below 3000'.

 

[Gym]

Clean hull, calm air and waters, no cavitation. Just can't rationalize the difference season to season. I don't think there's a lake in the state of Utah below 3000'.

Possibly if you can get to one of those lower lakes on a cool evening (in the 60s) you will notice a significant difference in RPM.