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2004 Honda BF90-- prop spun or water in carb?

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SaltyMatt

New member
Hello, I am a first time poster. I bought a 17' Lund and Honda BF90 three weeks ago (both 2004 model). The motor worked perfectly when I tried it out.

Fast forward to this past weekend and I took it out for the first time. The motor always cranks, always idles well, and puttered out of the no wake zone with ease. When I went to put it on plane the first time the bow rose up, tach went to about 3,000 and then the motor would rev and the bow would drop. I watched it one time rev from 3,000 to about 4,500 even as the bow dropped and speed decreased.

At first i would back off the throttle but as I kept trying it I discovered I could keep the throttle open and the motor would eventually catch up and the boat would plane. Once on plane it would run all day. After this, I noticed it planes normally about half the time and half the time it does not. If I put it in neutral I can open it up to 5k rpms easily and it doesn't stall.

I called the local Honda dealer down at the NC coast where I was and he thought it was a small drop of water in the carbs. He suggested I disconnect the fuel line and run the motor up to about 3k rpms and let the motor suck all the fuel (and any water drops) out. He said the water drop may only show up under torque. I did that and also drained the carbs with the drain screw and re-launched but same issue. The gas tests fine and fuel lines tested fine.

I am thinking it may be the beginning of a spun prop but not completely spun. When i put motor in gear (motor is off) I cannot turn the prop by hand.

The final confusing point is I went to trailer the boat and when I pressed the throttle quickly the motor sputtered almost off. I have read that the older carbureted BF 90s were set lean and would die down if you opened the throttle too quickly.

Any ideas if this is a complext carburetor/fuel problem or just the beginnings of a spun prop? The boat was garaged about 5 years without use before I bought it. Thanks for any thoughts!
 
The 90's do not like quick (pulling a skier) type takeoff.

You might have some issues with the carburetors, but let's check a few basics first.

It could also be a spun hub, but maybe not.

I hope you don't consider this insulting...but I do not know your experience with boats.....

Questions....

When you start out, do you have the motor trimmed all the way down and not trim up any until you actually get on plane? If not...try it.

If you do not have it trimmed down all the way, the motor could be cavitating and giving you symptoms of a spun hub.

Once you get it on plane, what is your top rpm with the motor trimmed out? You may have too much pitch in your prop. You should get somewhere around 6000 rpm.

Are you sure that it is running on all of the cylinders? On a hose, you can rev these up...but that will not tell you anything.

One other thing to try when the motor is struggling is to partially operate the choke on the engine and see if the engine speed picks up. If so, then it is definitely a fuel starvation issue and points to the carburetors. If you have a push to choke or a toggle switch to choke, just momentarily activate and see what happens. If you have a side mount box (with a key in the box), you may have to have someone in the rear of the boat, pull the manual choke out a little. Do not keep the choke out, the motor will definitely bogg down.


It might also help to move some of the weight in the boat to the bow.

If you have to get into your carburetors and you intend to do them yourself, you should concentrate on the transition passages. This motor has idle circuits, transition and high speed circuits. If you are going to do them yourself, the Honda carburetor manual is invaluable to step you through it. It is around $40 but well worth it. These carbs are not as easy to clean as many may suggest....if you want to do them correctly and only do them once.... http://www.amazon.com/Honda-Marine-...1AFO/ref=aag_m_pw_dp?ie=UTF8&m=A14VJQOXKKYWSY

There are many other things it can be.....spark plugs, fuel filter, compression issues, timing, etc. However, as I said....we will start with basics of operation first.

Mike
 
You can check for a spun prop on an outboard that size with a small jack and a block of wood. If you mark your flywheel so that you can tell if it moves, you can use the jack, with the wood on top to protect your prop, to jack one of the blades that stopped horizontally to the ground. Ideally you want to jack on the left side with the outboard in forward gear (if you have a right hand prop) to ensure that you rotate the engine in the proper direction.

MAKE SURE THE KILL SWITCH IS ACTIVATED.

As you SLOWLY jack up on the blade and the prop starts turning....the flywheel will tend to move VERY little or remain in the same position if the hub has parted internally.

If the flywheel moves in relation to the movement of the prop...the prop is likely OK.

You should only need to move the blade upward about an inch or so to make a determination.

This isn't an EXACT test but is much more reliable that trying to turn the prop by hand.

Another "basics" thing to check (and rectify) is how the outboard is mounted to the transom. If the outboard is not mounted correctly....that will cause you problems no matter how well it runs. Is the outboard extension length suitable for this hull? In other words is it too long?....to short?

A rule of thumb for MOST V hull or semi V's is to have the cavitation plate just about even with the bottom of the keel at the stern. It doesn't need to necessarily be exact but the closer the better. Slightly lower is preferable to being too high.

This is a common problem on boats that have been "repowered" and the wrong outboard extension case is used. It usually stems from the fact that guys will buy a "bigger motor" to get the added power and will opt for a "bargain" even when it doesn't match their hull.. This can usually be alleviated with a "transom jack" to raise or lower the outboard or a custom built transom "spacer" to achieve correct prop placement height.

Just a couple of more thing to worry about...but...then...that's why we have them. RIGHT?
 
Mike, thanks so much for your reply. I joined this forum last night after seeing all of your replies in hopes that you would, so thank you! You may be onto it with the trim issue. When I bought the boat I assumed that when you trimmed it down you stopped when it got to the two support rods but my bro-in-law showed me that those two rods will recess if you keep on trimming it down. I don't know if that much difference in trim could cause the cavitation or not but I will try it this weekend. I have a push-to-choke so I can easily try that also if the trim doesn't work--great idea. The prior owner just had a new carb kit put on it so I suspect/hope it doesn't turn into a carb cleaning issue but thanks for the manual link above. Mostly...thanks for your time replying to posts like this to help us less experienced guys out!
 
jgmo- Thanks for the reply! It is an original motor so hopefully the cavitation plate is at the right height but great tip for me to check. I plan to launch again this weekend so I'll check the spun prop too. Take care and thanks.
 
Mike,

Thanks again for your earlier reply. I was able to launch this weekend and the trim did it. It was not trimmed all the way down as I thought it stopped when it reached the two support rods that actually recess. Rookie mistake. . I also got it up to 5,900 rpms at WOT and it hit 38 mph. Thanks again for your time!
 
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