Honda BF90D won't run above 3400 rpm

S

ssobol

Active member
Normally I operate my 22 cruiser at sea level (Chesapeake Bay). It has an 08 BF90D engine with about 200 hours on it. Last time I used the boat (about two weeks ago) everything worked fine. With the prop that is on it the normal WOT rpm is 5600.

This week I took the boat to a lake that has an elevation of about 1000' MSL. I found that the engine would not run above ~3400 rpm (about 12 mph). Below that speed it works fine. I cruised for a number of hours at 2000 rpm (~7 mph).

If I try to go faster the boat accelerates normally until about 12 mph, and then won't go any faster. The engine rpm peaks at ~3400 and then will fall off a bit if I keep advancing the throttle. When the engine is in neutral it will go above 3400 rpm with out any problem.

My question is am I experiencing difficulty because of the altitude or do I have an engine problem? I have not tried running the engine at the normal altitude yet.

If this is an altitude issue I would not have expected 1000 ft. to make such a big difference in the engine performance. I know that people who go to Lake Powell have to adjust their prop pitch to compensate for the altitude, but that is 4000' plus higher temps.

If this is an elevation issue, is there a way to predict/calculate the proper prop pitch in advance (i.e. pitch change/1000 ft)?
 
Sounds exactly like the problem I had 2 years ago with my 115 Yamaha, mine was ethonal related and the problems it caused in the VST. As I am not familiar with Hondas fuel systems I cannot say with any type of certainty, but the symptoms are identical
 
That doesn't sound like an altitude problem but rather something else. I'd suspected fuel starvation - maybe a clogged filter etc.
 
Not an altitude problem. I agree that it is a fuel problem. Start with filters, both in the line, and if there is any in the Honda 90, under the cowl. (This should be an injected engine. There may be a filter or water separator under the cowl). Next, you look at the fuel hoses, the selection valve (could be that it is a little off, Port or Stb..and restricting. How does the fuel primer bulb look, if fuel starvation before the valve, it will be flatter, or soft.

Other areas, include anti siphon valve, fuel hoses them selves, the pickup and the tank vents. It could also be a problem with the injectors or injector pump--but less likely.
 
Not long after I made my initial post, I went out again and the engine ran fine. The WOT rpm was about 5K. It seems that the BF90D switches modes or something about 3300 rpm, you can sort of feel it take off after that rpm.

It has run fine for about 7 hours so far.
 
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