Logo
FULL SITE MENU

BF90 Reving up

C

Captbuzz

New member
I have a 24ft pontoon with a bf90 on it. The boat and motor only have 400 hours on it and my father had it serviced twice a year for the last 18 years. Today for the first time I was driving about 10 mph and the motor started reving up on its own and I would lose power. I tried to accelerate but every time I did the RPMs would rev up even higher. The more I accelerated the more the rpms would rev up. I ended up stopping for about ten minutes but never turned the motor off because I was afraid it would not restart. When I went to take off the motor acted fine and it never did it again. The motor did this for over an hour, but after stopping it went away. Why would the motor do this and do I need to be concerned about the lower unit or anything else?
 
Agree with Alan....

Bur take a close look at your propeller hub. They can slip and then "catch" when going bad. It will provide thrust again temporarily until it slips again so you need to take the prop off and inspect so it doesn't have a chance to leave you stranded.

Good luck.
 
Agree with JGMO. You likely have a sprung prop that slipped, then it caught hold again for a while. Pull the boat. Put the engine in gear. Use heavy gloves or wrap a towel around the prop and try to physically move it back and forth. If it moves, it's spun. If not, pull the prop and very closely inspect the rubber bushing where it meets the hub spindle and the blade piece. You will likely see the rubber raised a bit. If any of it is raised, you have a spun prop. Depending on the type of prop, they can be refurbished for about $120 to $150 through most any marine repair shop. But it usually takes a few weeks. So in the meantime, buy a new prop along with a new thrust washer, flat washer, castle nut and SS cotter pin and use those. When you get the refurbished prop back, store it on the boat, along with the thrust washer, flat washer and castle nut, plus one or two SS cotter pins.
 
I agree that it's possible that the prop hub is spun - emphasis on "possible".

I was considering a boat moving at 10mph. Noticing this issue for the first time generally requires near full power in my experience. Pretty sure a 90 hp Honda on a pontoon at 10 mph was nowhere near full power.

All due respect, I'm afraid I will have to disagree regarding a prop "moving" being a valid test for a spun hub. I generally do this test for other reasons, and find that moving a prop with my foot on a prop blade while in gear not all that difficult. The motors are not THAT hard to turn.

A proper test for a spun hub generally involves marking the prop nut and prop hub with magic marker. With marks installed, you try to duplicate the slipping, and if successful, check to see if the marks are still aligned. If still aligned, that prop hub is not the issue. MUCH easier and more practical as the boat can remain in the water too.

I would note also that on a pontoon boat, there are a few other issues that might cause temporary over revving/unloading/cavitation. Physical prop damage being pretty high on that list.

50 years experience on pontoons, lately powered with a Honda 90, still has me thinking thinking a gob of weeds, a rag, or a piece of rope would be the more likely culprits here.

I would add only that if this prop was original, at 18 years old, the likelihood of a spun prop not that hard to imagine..... -Al
 
Last edited:
Alan Hicks said:
I agree that it's possible that the prop hub is spun - emphasis on "possible".

I was considering a boat moving at 10mph. Noticing this issue for the first time generally requires near full power in my experience. Pretty sure a 90 hp Honda on a pontoon at 10 mph was nowhere near full power.

All due respect, I'm afraid I will have to disagree regarding a prop "moving" being a valid test for a spun hub. I generally do this test for other reasons, and find that moving a prop with my foot on a prop blade while in gear not all that difficult. The motors are not THAT hard to turn.

A proper test for a spun hub generally involves marking the prop nut and prop hub with magic marker. With marks installed, you try to duplicate the slipping, and if successful, check to see if the marks are still aligned. If still aligned, that prop hub is not the issue. MUCH easier and more practical as the boat can remain in the water too.

I would note also that on a pontoon boat, there are a few other issues that might cause temporary over revving/unloading/cavitation. Physical prop damage being pretty high on that list.

50 years experience on pontoons, lately powered with a Honda 90, still has me thinking thinking a gob of weeds, a rag, or a piece of rope would be the more likely culprits here.

I would add only that if this prop was original, at 18 years old, the likelihood of a spun prop not that hard to imagine..... -Al
Click to expand...


Thank you everyone for all the advice, I will be checking all of these solutions and will definitely let you know what I find. Thanks again for your advice!
 
Alan,

Admittedly, I know nothing about pontoon boats - never owned one. And all of my Honda experience has been with the BF 225 or BF 50. However, manually moving the prop on a 225 while it is in gear is dang difficult, and a spun prop would show up using that procedure. But, maybe not so much on a 90. Looking for telltale rises on the rubber hub is a pretty definitive test.

OK on marking the prop nut and hub with a magic marker. Good procedure if you can get to the prop nut and hub while in the water. That's not possible on my boat unless I take a swim.

I estimate that I have had to deal with at least 20 spun props over the years and I've noticed that often times the initial spin out doesn't last, but will show up again, more seriously each subsequent time.

Regardless, a detailed examination of the prop and lower end is called for, and for that, the boat should be hauled out, IMO.
 
Back
Top