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iab vacuum diaphragm

Garygin

Garygin

Regular Contributor
Ok . I have a 2002 225 hp. Runs great up to about 3700. Can’t get anymore out of it. Changed all filters , compression 200 on all cylinders on a cold engine, checked all plugs. So chawk_man… who always has the best info suggested to check the Iab vacuum diaphragm. Plunger moves freely. If you draw air into it the plunger goes in, release air it goes out . If you push plunger in and cap the hole where the vacuum line hooks up it doesn’t hold the plunger in. Is this diagram shot? Also if it is someone has to make the same one . I really don’t want to buy the whole cover for 700 just to get a diaphragm.

Thank you, Gary
 
Hi,

I would test the diaphragm differently.

Instead of pushing it in, use a hand vacuum pump (not expensive at Harbor Freight) and pull an 18" vacuum (or less) on it. Then, simply pinch the hose off.

I think that might be a better/more accurate test.

If it does leak, I don't know of an alternate replacement but I would agree that you might find something that would work.

Lots of 60's and 70's car vacuume dashpots still available. Obviously some fabrication/tweaking will be needed.

I wonder too how close the dashpot for the BF 25 through 50 throttle dashpot might be?
Item 1 in link below.

Good luck.
 
Attached is the complete write up I did on the IAB and the diaphragm.

I don't think Jimmy's part will work. You need a rather long, flat diagonal arm that attaches to the IAB baffle arm.

I don't think the diaphragm itself is repairable, I would go through Honda auto parts catalogues for the J35 engine. You may find a suitable replacement there. If you can find a similar diaphragm with a correctly oriented plunger arm, then you could modify the arm by welding the front part of the old arm to the new one. Just make sure you get the throw distance correct.

As a side note, it's really stupid for Honda to not sell the diaphragm as a separate part.
 

Attachments

  • Honda 225 Intake Air Bypass.pdf
    451.4 KB · Views: 46
Yes, suggesting the carb throttle diaphragm was a big mistake on my part.

It isn't even a vacuum diaphragm! It's more of an air pump than anything else!
I guess I just got ahead of myself there.
Apologies.

I certainly agree with Bill about Honda being wrong by not offering that part separately.

It's the same senseless greed that drives decisions like making you buy an entire throttle body to get a TPS sensor or upcharging 4 and 5 times the price of their fuel pumps.

Somewhat disgusting but it seems to be the norm in industries these days. While they could easily choose to buck that trend and SUPPORT their customers, they don't.

Bean counters win again!

Despite that though....

....Happy Thanksgiving!
 
Thank you all for your help. It is always appreciated. Some great people on this site.
Happy Thanksgiving
 
Jimmy - At our age, brain farts occasionally occur. And yes, Honda design engineers have had a few puzzling design failures over the years.

Happy Thanksgiving!!!!
 
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