Honda 150 upper rpm range
I've got twin Honda 150's and after getting on step, the motors will rev to about 6100 (w 15" props) and 5800 w 17" props). I don't run the boat WOT so after on step I'll cruise at 4400-4600 rpm's.
The other day while pretty loaded with guys and gear I was running the 15" props and WOT I was getting 5100 rpm's out of the stbd motor while the port motor would spin up to 5600.
Just felt like the stbd motor was not up to snuff, so the next day I changed out the racor fuel/water separators and back in the water we went. Empty boat and half fuel same thing happened. While getting on step boat ran the boat up to 6000 rpm's, then I immediately throttled back to 5700 rpm's. After about 5 minutes could feel the stbd motor "drop off" down to about 5400 and the throttle was pushed all the way to the console.
What gives? The port motor doesn't behave that way at all, power on tap all the way. No alarms, no rough running, nothing except you can feel the boat slow down and hear the motor drop in pitch/sound. Both motors are fed from the same tanks but each has its own racor and I changed both.
So boat is now at AMD and they can't find anything wrong, hooked up to computer and all. (Motors are 2008 models with about 1400 hrs)
The boat was serviced in Homer in July with valve adjustments, high/low pressure motor fuel filters, oil changes, plugs and I've only put on about 20 hrs or so since I just got it.
Homer mechanic says check coils & plugs (which AMD did and said all good). AMD is changing out the high & low filters again (I did have to empty racors of some water in the fuel and there was some debris in the bowl, kinda silty looking so I swapped those out a few days ago).
Since it's there the AMD mechanic is gonna check the valve clearances again since that was recently done and maybe not properly.
They also said anywhere over 5000 rpm's is all normal for those engines and I could accept that if they revved to let's say 5400 and stayed there consistently and both motors did that but for the one motor to noticeably drop off is suspect to me. They also said the rev limiter could kick in over 6000 rpm's and settle the motor back but all the way down to 5400 unloaded, 5100 loaded? That doesn't sound right either.
Anyway will pick boat up today as I gotta run to Green tomorrow for a pickup. Just confused as the motors run fine, no alarms, no pulsating indicating a fuel flow or spark issue. Will see how they run tomorrow and post back.
I guess the next thing would be maybe new racor housings as those are kinda old so maybe sucking air?
All else fails maybe a trip to Ron's Honda
I feel like the motors should run right up to their upper rpm range and can adjust that by different pitched props.
Jim, I have twin Honda 135's, same motor as your 150's EXCEPT that the 150 has a special valving sequence (or maybe more valves...) that kick in over 4500rpm, that is what gives them both the 15 extra hp and better high end performance. What I would suspect is that the stbd motor has a problem with this feature, it is just not kicking in on this motor. That is why the motor scopes out fine, yet still doesn't perform correctly.
I disagree with the mechanic that says these motors are fine with any WOT above 5000rpm...not that I personally know that much, but because all the experts I read say anything less than 5800rpm on a 6000rpm max motor will put a strain on it.
The operating RPMS for the 150s is 5000 to 6000 per Honda specs. This info is in your owners manual.
If propped right you will hit right at 6k with a lite load and the mid 5s loaded at full throttle.
Sounds like the one is starving for fuel.
Here is the link to Honda if you don't have the manual... http://marine.honda.com/outboards/motor-detail/BF150