honda BF90D surging in mid RPMs

ssobol

Chief Petty Officer
Joined
Sep 3, 2010
Messages
503
I have a Honda BF90D. When the engine is running slow <1200-1500 rpm it runs fine. Between ~2000 and 4000 rpm the engine will not maintain a steady rpm. It will drop a couple of hundred rpm for a second, recover, then drop again. It will keep doing this continously and it is pretty annoying. Once the rpm is above 4100 or so the engine runs smoothly. I was out for 3 hours today and the engine operated consistently throughout.

My boat has two tanks and it operates the same on both tanks. The fuel in the tanks is from different sources and was purchased at different times.

Any ideas would be helpful. Thanks.
 

sportfishcol

Recruit
Joined
Nov 26, 2012
Messages
1
Re: honda BF90D surging in mid RPMs

Hey there, I have the same engine and its doing the exact same thing! I am no expert but have researched a little and it seems like it may be something to do with the vapor separator,I have just drained the fuel out of it and replaced the very expensive high pressure filter inside of it, i havnt had the chance to use it yet but il let you know how it goes cheers,col.
 

ssobol

Chief Petty Officer
Joined
Sep 3, 2010
Messages
503
Re: honda BF90D surging in mid RPMs

Hey there, I have the same engine and its doing the exact same thing! I am no expert but have researched a little and it seems like it may be something to do with the vapor separator,I have just drained the fuel out of it and replaced the very expensive high pressure filter inside of it, i havnt had the chance to use it yet but il let you know how it goes cheers,col.

Just got back from two days on my boat. Before I set out, I drained the vapor separator in my engine and drained the water separator in the engine and the external one. The engine behaves the same way. In the 3000's the rpm will drop a couple of hundred and then recover constantly. If I set the rpm above 4000 (i.e. 402) it stops surging and runs smoothly. With the rpm in the high 2000, it still surges, but not as noticeably.
 
Top