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75hp outboard fuel starved at WOT

J

jadunn02

New member
I have a 09 honda 75hp 4strk about two weeks ago I started having problems with my outboard surging at WOT. I have changed external fuel filter, all external hoses and still have the same problem. I have replaced all internal filters.
(1. if I connect fuel tank straight to engine problem goes away. tank-hose-bulb-hose-engine)
(2. if new external fuel filter is added to (1.) problem comes back)
This only happens at WOT. When this is happening if I pump the bulb up about 10 times it becomes hard and the problem goes away.
However, in about 10 minutes are so, it happens again. I repeat the process of pumping the bulb up and it goes away for about 10 more minutes. Note this only happens during WOT. all other times runs find.
headknocker.gif
 
It is obvious that the added restriction of the external filter is causing fuel deprivation.

Several questions...

What is the serial number of the engine?

Is the external filter something that was recently added?

If you look at your filter on the top of your engine, does the hose from it go to the top or bottom fitting of the fuel pump?

I know....a lot of off the wall questions.

The early versions of this motor had a fuel pump problem that would cause fuel deprivation if the boat was run at full throttle with a heavy load.

The routing of the fuel line from the filter will tell me which pump you have.

The problem could be something else, but it is good to eliminate the obvious first.

Mike
 
hondadude said:
It is obvious that the added restriction of the external filter is causing fuel deprivation.

Several questions...

What is the serial number of the engine?

Is the external filter something that was recently added?

If you look at your filter on the top of your engine, does the hose from it go to the top or bottom fitting of the fuel pump?

I know....a lot of off the wall questions.

The early versions of this motor had a fuel pump problem that would cause fuel deprivation if the boat was run at full throttle with a heavy load.

The routing of the fuel line from the filter will tell me which pump you have.

The problem could be something else, but it is good to eliminate the obvious first.

Mike
Click to expand...

External filter has always been on outboard. I change canster every year.
motor is a 2009 model " s/n BBAJ" BF75D. Line from top low pressure filter go into top.
 
Well, so much for that theory!

Think if anything was changed or worked on in the motor. Double check all of those items for tightness and that they are clear of debris.

Make sure that the seal is on the canister. Sometimes they fall off or get dislodged during installation.

When you have to pump up the bulb, if the bulb comes up to its original shape quickly, then there is most likely not a "restriction" between it and the tank. Although, there could still be a loose connection to allow air into the fuel flow.
Just to be sure there is no venting problem, make the engine fail, then pump up the ball again and loosen or remove the fuel tank cap to eliminate the thought of a clogged vent. If it runs good, then you have a vent problem.

Look especially close to the rubber grommet area where the fuel line goes into the engine for a pinched hose.

I suppose it is always possible that the fuel pump is going bad, but not very likely.

It could also be a bad pickup in the tank. It could be drawing more air then fuel.

As a test, you could insert a clear plastic hose in various places along the fuel line and watch for any air bubbles. If you see bubbles, then move it back along the line, until they go away. When they go away, you will have just passed the location of the problem.

Before you do anything with a clear hose, you can run the engine without the engine cover and have someone watch the fuel filter on the top of the engine. If you are sucking air, you may just see bubbles developing in the top of the filter. Of course, as it fails, you will probably see the fuel level reduce in the filter.

Unless something turns up very obvious, just approach this methodically and write down the results as you do the tests. I typically forget what I did, after a bunch of tests. It is easier to sit back and look over the results and possibly come to an "AH HA" moment.

Others may jump in with some better checks. I just know, that before we found the original fuel pump problem, the Honda Tech Rep and I spent several hours of testing and recording before coming to the conclusion that it was a faulty pump design. We also had fuel pressure gauges with us too.

Others will probably jump in here with some further suggestions.


Happy hunting.

Mike
 
I just got done chasing down the same exact problem. it was the factory crinp on the fuel line connection on the motor. it was snug enough not to leak at idle, but was losing vacuum at top end. new tight connection, problem solved.
 
crankbait said:
I just got done chasing down the same exact problem. it was the factory crinp on the fuel line connection on the motor. it was snug enough not to leak at idle, but was losing vacuum at top end. new tight connection, problem solved.
Click to expand...

Was this on the factory fuel line outside of cowling?
 
jadunn02
i have a 08 bf90d and had the same issue. Hondadude helped me by telling me to replace the low pressure fuel pump.( there was a design change) seems that it could not supply enough fuel at WOT. not sure if this is what your concern is but sounds like the same thing i had. there was a upgraded one for me.
 
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