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Intake Air Bypass on BF 225

C

chawk_man

Silver Medal Contributor
Looking for some help.

Today I was pulling a 200 hour maintenance on my BF 225. Went to change out the HP fuel filter. To do that you need to disconnect the IAB vacuum diaphragm and move it aside. First surprise - the dealer that I've been lauding for all these years pulled the last 400 hour maintenance and whoever the ham-hand was that did the hp filter stripped the heads on the 2 screws that hold the diaphragm. Had to remove the whole intake manifold cover to get to it, then ended drilling out and easy-outing the two bolts. Bummer.

In the process of doing all of this I noticed that the IAB mechanism was totally frozen - wouldn't budge. I soaked it with carb cleaner (as recommended in the Helm Shop Manual) and then PB blaster and can get it to move a little using a pair of pliers and screwdriver. It's supposed to move easily. I will let it soak in some PB Blaster overnight, but this needs some serious rehab.

My main question is to find out if anyone on the forum has dug into this mechanism to any great degree? I'm pretty sure I can disassemble the whole thing, including the flaps in the intake manifold cover, BUT, I'm worried about how much tension is on that coil spring. How difficult is it to get the spring re-installed correctly? Any other precautions?

My other main question is what does thing thing, the IAB, do in the first place? I'm pretty sure that it has been in a failed state for a long time, but the engine performance seems fine, so if it's not working, what are the consequences?
 
I can't answer the first part of your questions, but as for what it does....

It is used to "optimize the resonance-charging effect with the low and mid range engine speeds and to optimize the insertia-charging effect with higher engine speeds"...."the system thus maximizes the low-end and mid-range torque and high-end output".

I copied that from the manual. If you have an older shop manual, there is an Operation Section. I copied the above from there. There is more explanation, but the above quotes summarize the section.

I seem to remember, elsewhere in the manual, it operates at startup also.


Mike
 
Thanks Mike. Not sure what all that means. To me, it looks like the the way it operates is that a given level of vacuum moves two in-line baffles in the intake manifold cover, diverting the direct flow of air into the manifold. At rest, the baffles are parallel to the cover. As more vacuum is applied, the baffles move toward being about 45 degrees off perpendicular to the cover. I'm not sure what effect that air diversion has on operating performance.

If I don't hear from anyone who has fooled with these things for a couple of hours, I guess I'll see if I can get it apart and get it operating correctly.
 
UPDATE: Well, using copious amounts of WD-40 and a penetrating fluid, I got to the point where I can move the baffles with a pair of pliers applied to the spring-loaded lever that is operated by the vacuum diaphragm, but can't get it any looser. That rod and the baffles they operate should be very loose in order for the vacuum diaphragm to maneuver it. I suspect that there is some sort of seal between the spring-loaded lever and the rod the baffles are connected to. I considered removing the baffles and trying to pull out the entire rod they connect to, but then on closer inspection, those baffles are connected with fluted screws and a Teflon backing, so they are definitely not designed to be removed. I think the reason for that is that if one of those screws ever came loose, it would find its way into the intake and the top of a cylinder, which would be a disaster.

The best advice I've gotten locally is to soak it in motor oil overnight, which it is doing now. I would really like to avoid paying almost $400 for a replacement, but it looks like that may be unavoidable.

At this point I'm open to any and all suggestions.

I'll post results from the overnight soak.
 
Oh well. Nothing worked - could not get it loose enough for the vacuum diaphragm to work it. So I reinstalled the IAB with the baffles fully opened so I could get the grand kids out on the water this week. Ordered a replacement from boats.net. When I get the new one installed I plan to take apart this malfunctioning one and find out what happened. Will let folks know.
 
to @chawk_man thank you from a fan-- i've been dealing with a nightmare 2015 BF225 with all manner of symptoms, so i've been all over the place on the boards on this motor. i am always appreciative of seeing your takes, they are always reasonable and almost always right! no small feat. anyway i'm in the middle of a wiring harness replacement, which led me under the IAB cover, revealing not only stuck baffles but several cups worth of sea-water and sludge mixture. fun! explained the corrosion in the wiring harness, however, as the engine seems half drowned. huge sigh.

so I WD-d and worked the baffles but it was obvious that the vacuum pressure was never going to overcome whatever corrosion had fouled up the bearing in the baffles, so i came up to the computer to order a new IAB. After my shock and awe at the part cost (it better damn well do something in there for $420!!!), i figured i'd head over to this forum and check in on the problem and there was ol' chawk_man working it through on a lonely thread. I appreciate you man. thank you for your service!! from San Diego CA.
 
chawk_man said:
Looking for some help.

Today I was pulling a 200 hour maintenance on my BF 225. Went to change out the HP fuel filter. To do that you need to disconnect the IAB vacuum diaphragm and move it aside. First surprise - the dealer that I've been lauding for all these years pulled the last 400 hour maintenance and whoever the ham-hand was that did the hp filter stripped the heads on the 2 screws that hold the diaphragm. Had to remove the whole intake manifold cover to get to it, then ended drilling out and easy-outing the two bolts. Bummer.

In the process of doing all of this I noticed that the IAB mechanism was totally frozen - wouldn't budge. I soaked it with carb cleaner (as recommended in the Helm Shop Manual) and then PB blaster and can get it to move a little using a pair of pliers and screwdriver. It's supposed to move easily. I will let it soak in some PB Blaster overnight, but this needs some serious rehab.

My main question is to find out if anyone on the forum has dug into this mechanism to any great degree? I'm pretty sure I can disassemble the whole thing, including the flaps in the intake manifold cover, BUT, I'm worried about how much tension is on that coil spring. How difficult is it to get the spring re-installed correctly? Any other precautions?

My other main question is what does thing thing, the IAB, do in the first place? I'm pretty sure that it has been in a failed state for a long time, but the engine performance seems fine, so if it's not working, what are the consequences?
Click to expand...

I went through the same thing on my motor. Took the entire assembly apart and got it cleaned and completly freed up only to find a broken part on the vaccum motor. Ended up buying new also.
 
chawk_man said:
Rick,

I wrote up the whole process. Will try to upload here. If it doesn't upload, send an e-mail to [email protected] and I will reply with the write up, including pictures.

View attachment 23073
Click to expand...
Glad this old thread came back to life. I checked the IAB on my 225, and the previous owner had zip tied the actautor so that the baffles were perpendicular to the cover, in other words zero air was able to get from one side to the other. I’ve had idle/seems like fuel problems.
Any idea why the baffles would be in a permanent “closed” position?
Taking the zip tie off, the baffles moved rather freely. They were not seized up, but needed a lil work to get to where a vacuum would move it
thanks
 
Bill , I have completely dismantled a number of these, it's the only way to fix it properly. I simply put a good quality thread lock on the screws that hold the butterfly plates, never had as problem and once the shaft is greased up, never had one seize a second time
 
Ian. Thanks for the useful input. The one I dismantled had the outer C ring totally rusted away and the shaft outside the seal was badly pitted. So I replaced the whole thing. The original problem was that the upper cowling did not seal properly and allowed saltwater to get in there.

Do you have any idea why someone would zip tie the baffles in the open position? I don't.
 
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