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BF200A2 drop in RPM

C

Chachy71

Member
ISSUE: Port engine loses RPM, the old owner complained there was something wrong with the port engine.

BACKGROUND
I have twin BF200 A2 with twin external RACOR. The engines have less than 900 hrs on them. The old owner deferred maintenance which I'm correcting. I have replaced the RACOR's, low pressure fuel filters (the old owner ran without low pressure filters) and the HP filters by the VST. The port HP filter contained some gunk, not a lot but some. I drained the VST and the gas looked clear and bright, no debris.

I poured Sea Foam in the gas tank. I have not pulled the tops of the gas tanks for a visual.

My initial run both engines hit about 5250 RPM. About an hour later the port engine dropped about 750 RPM then dropped to about 4000. I started and stopped the engines several times between runs. On one restart the port engine operated great and ran about 5000 RPM's but would occasionally the RPM's would drop.

When I pull back from full throttle to neutral the port engine usually dies.

I am not getting any codes. I have the computer with HealTech software and the system isn't throwing any codes.

NEXT STEPS
I have a fuel pressure gauge. Should I check to see if I am getting full pressure (around 41 psi if I remember from the forums) or just move ahead, check the screen on the fuel pump, check the fuel rail, and check the fuel tank pickup?
 
Check fuel pressure under load when problem is occuring. This is a PIA with these motors because of where they located the fitting port but a proper diagnosis can save a lot of time and money.
 
Copy, the fuel pressure fitting is a bear to get too. I'll check the pressure this weekend. I'm also going to check the fuel hoses for cracks/leaks and replace the bulb since its old.
 
Agree with Ian about checking fuel pressure as a first step. If out of spec, get back to us for possible remedies. (I'm not sure what the spec is under load - at idle it should be between 42 and 49 psi.)

Also, when engine is acting up feel the primer bulb to make sure it is not partially collapsed. If so, you may have a clogged vent to the fuel tank (if you have separate tanks for each engine.) or you may have a clogged fuel pick up tube (assuming you have a separate pick up for each engine.)

When engine is acting up, rapidly pump the primer bulb. If that straightens it out, you possibly have a failing LP fuel pump.

When engine acts up, look at the fuel level in the LP fuel filter bowl. Normal is 1/3rd to 1/2 full under load - at least that's what it is on my engine.

Consider running a clear plastic fuel line from the Racor directly to the onboard fuel/water separator and look for air bubbles when engine acts up. Then run that line from the LP fuel filter directly to the LP fuel pump and look for air bubbles.
 
Finally got around to checking the fuel pressure when it was in dry storage, rock solid at 45 psi.
Swapped the fuel bulb and tried to pump it during the problem with no change.
LP fuel filter looks like yours 1/3-1/2 full
The filters don't look like they have bubbles
Racor bowl looks fine.

I swapped fuel lines, so port tank running stbd engine and vice versa, but I haven't run it yet.
I might try and tear the VST out Monday and see what that looks looks and check the high pressure pump screen but I don't have any of the gaskets, so hoping that goes apart clean.

On a side note Honda is proud of their VST gaskets and O-rings, $8 - $11! Yikes.
 
If fuel pressure is good then you are chasing tge wrong problem by tearing down you separator. Have you checked your sparkplugs and compression? Cover the basics first. Also, carefully check the ignitors for hairline cracks when you remove the spark plugs.
 
I cleaned the fuel pump this afternoon and it had a lot of gunk in there.

I replaced the spark plugs but didn't check the coils. I'll take a look at the coils when I check the compression.
 
The gunk seemed to be the problem. Ran fine at 4k from the yard to my mooring ball, about 45 minutes, the east wind keeps a constant 2-4 ft swell and couldn't really get it faster than that without pounding. Then did a couple of WOT runs in a small bay without the swells, hit 35 kts. It responded great to all throttle commands. I'll call that a win.

Port engine will get up to about 5200 and stbd 5500 so something still not 100% but I'm happy for right now.

I did notice the right pressure relief valve is stuck open and the discharge hose isn't connected. Of course I noticed that after I got everything was back together during engine trials. Something to be fixed another day.
 
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