Honda bf90 lower unit issues

I have a pontoon with bf90, today going down lake felt small vibration at half throttle and then motor changed tunes and boat went slower. I advanced throttle motor acc . Fine but went no faster almost like a clutch slipping, rode back to dock about twenty minutes just babied it back trying not to do nothing to damage anything docked it and didn't see anything visually wrong with anything. Putting it on trailer accerlerated hard and it acted fine and loaded it up. Just wondering what to do I just change all the fluids in motor and lower unit so they are fresh and the lower unit was still going into forward and reverse like normal, any ides are useful thanks in advance!

Remove the bottom gear case screw and see if there is any metal pieces on the screw. If the lube and the screw look ok, most likely, you have spun the hub of your prop. Try another prop and your problem will probably go away.

Mike

Mike thanks I took the drain screw out and hardly nothing at all oil looked good except for just a little moisture which was there when I changed fluid and installed new seal washers. I am going to change lower oil again to get the rest of moisture out. What type of prop would you recommend as far as pitch and size and so on if I pick up a cheap alum one to get by until I can get this one rebuilt. I'm running a bf 90 on a 25' crest pontoon. Thanks as always!

Glad the lower unit oil looks ok.

If you currently have a stainless prop and you are getting about 6000 rpms at full throttle, then an aluminum with about the same or one pitch larger should get the job done.

If you are not getting 6000 rpms, then go with the same pitch and not larger.

My guess is you will be somewhere around an 11 pitch prop or so.

A good prop shop should be able to replace the hub of your stainless, it the test prop works for you.




Mike

Thanks mike, got the old prop off had to use some heat because of no anti sieze. It was a 13.25 x 17 prop so i ordered a michigan alum vortex prop with hub it was a snap to put on and nice parts. It is all together and topped off gear lube and planning on testing it out on Saturday. I will let u know how it goes.

I still think your prop has too much pitch. I will be really surprised if you get even close to 6000 rpms. Check the performance reports on Honda's web site. http://marine.honda.com/products/performance

There are no pontoons with a 90 carburated engine, so do not put in any horsepower, and it will list all the different size pontoons with different size motors. There is a 25 ft pontoon with a 225 hp and a 17 pitch prop. That and some of the others should give you some idea of how the boat should perform. Click on the boat name and see the detailed reports.

Mike

Mike after reading your post I agree with you the prop seem to fix the problem but my tach doesn't work so I can't get a reading. Any ideas on whether it is the tach or wiring it is stuck on 4000 Rpms and doesn't move the hour meter still works but that is it. It seems the motor struggles to propel but until I get tach straighten out I'm kinda guessing . I will tear into it tonight and see if I can get it going, if any suggestions I'm all game! Thanks again!

You are right on guessing without a tach.

You should have 12v at the gauge when you turn the key switch to on. That will normally make your tach go to zero. Depending on the gauge. If it is a Faria Gauge, the posts to check are marked BAT and GND. If it is a Teleflex, the posts to check are marked IGN and GND.

If you are getting power to the gauge and it does not go to zero, then the gauge is most likely bad.

You can try rotating the setting switch on the back, but it probably will not help.

If you do get it to work, the Faria setting on the switch should be "1", the Teleflex setting is 2P.

Mike

Mike, got new tach finally installed cranked up and it actually worked . At what rpms should my idle be and I'm going to try and get a reading on the prop this weekend. Is 6000 rms at wot the gospel or a little lower as soon as I get back in water will be looking for more expert advice, everything you have said so far is spot on and I appreciate all the help!

Idle should be 950 plus/minus 50. I usually go a little on the high side.

Get as close to 6000 rpm WOT as you can.

Mike

Ok mike, I got in water with tach and the 13.75 x 17 pitch prop at wot I was at 5400 rpm, so I went to turning point prop and used there prop wizard to calculate prop. I put all my info in andit recommended a 14x13 pitch prop to get to 60000 rpms at wot, so igot one put it on and it fell flat on its face it would turn up to 6000 but would go nowhere just like spinning in place. So I repropped with my old one and run perfect at wot at 5400. Was it the diameter or pitch ,I looked at my neighbors pontoon same basic size but it has a 100 Yamaha it has a 13.5 x 15 pitch prop. Any help would be a blessing and I'm going to call turning point also and speak to them personally! Thanks in advance for all your help!

Sorry the prop I have is 13.25 diameter and not a 13.75 as I have typed above!

I was wondering if the prop shaft holder on a honda bf90 was hard to replace and if the ring that cover the prop is corroded and chunky out if it effects anything. Mine is starting to do that but don't want to tear into if not needed.

As long as the prop shaft seal is good (not getting water in gear lube) and the ears that keep the holder bolted on are in pretty good shape, I would hold off.

It is not difficult to change the holder. You have to pull the drive. Remove the water pump (a good time to change impeller). Remove the shift shaft (most likely you will break the plastic holder getting it out if there is much corrosion), then you can remove the bolts holding the holder and pull it out. You will have to remove reverse gear/bearing and install two prop shaft seals and needle bearings.

By the way, how did the prop size search turn out?

Mike

Thanks mike put a 14 x 13 on and motor just spun up and went absolutely nowhere, so I called turning point prop and told them and the suggested a 13.75 x 15 so I'm going to try it in morning and see they said it should put me about 5800 or 5900 rpm . I will let u know thanks for all the help!

Ok I put the turning point 13.75 x 15 prop on this morning and wot Rpms went straight to 6000 and top speed about 17mph but, I am a little disappointed with my mid range now I'm have to turn around 5000 to run 12 mph instead of 4400 rpm with my 13.25 x 17 prop.! Since I run at mid range with my pontoon more than wot which prop is best suited and what about gas consumption . As always thanks in advance!

Did you lose any full throttle speed? Sounds like you may have lost some speed, but you did not say

It's difficult to say whether 12mph at 5000 rpm is using more fuel than 12mph @ 4400rpm. At 4400rpm and a larger prop, the engine is working harder than it should, like your car running in high gear before the rpms are ready for high gear. On the other hand, with the lower pitch prop and running at 5000 rpm, is using more fuel than it is at 4400 but the motor is not straining. I could not tell you how much difference, if any there is.

You could always get a small tank and run each prop for an hour and check to see how much fuel they each use.

Bottom line, if you hare happier cruising at a lower rpm, a small difference in price of fuel is the price you pay.

The folks at Turning Point seem to be working pretty well with you and deal with prop differences all the time.

Maybe a compromise to 13.75 x 16 would get you to a close compromise.

Not being an expert....I keep changing props until I get the right one...

In general.....an increase of 1/4" in diameter, decreases rpm about 100 or so.
....................an increase of 1 pitch decreases rpm about 100 or so.
The numbers do not always work out the same from boat to boat, but it is a place to start.

Mike