Topic: There's something not right about this (airbox)

[gregimotis]

So, I now own two complete airbox sets (old but pretty good condition) for my 76 750F1, two sets of old boots and one set of new boots.

The touble is that none of the boots create a solid seal on the airbox side, which means that raw air is bypassing the filter.  It isn't a lot of space around the boots, and some of them fit pretty close... but some have a couple milimeters bewteen boot and box.

When I mount the airbox and carbs, the space is decreased but I don't really think it's tight enough to keep air from sucking in.  Is there a trick I'm not aware of?


I guess I can simply build up a neck with some electrical tape or something, but I'd rather do it right.

[seaweb11]

Photo?

[gregimotis]

That'd be best, but I don't really have a camera.  All I can say is, the boots have a 'trumpet' insode the box.  It seems like what is supposed to happen is the carbs pull the boot out and the 'trumpet' shape creates a seal.  Trouble is, my carbs don't sit far enough away from the airbox to make that seal tight.  Maybe tight enough on 1 and 2, but I could stick a popsickle stick through the space on 4.

[Bob Wessner]

I don't know if it will be enough to make a difference, but when refitting my carbs and airbox last year, I was having minor fit problems. What I found was that the problem can stem from the intake manifolds running from the carbs to the head. There is a slight elbow and if the angle is either too high or too low on any, the alignment of the carb bank and then the tubes to the airbox can be off. Just a thought.

[MrZxp]

All I can say is, the boots have a 'trumpet' insode the box.  It seems like what is supposed to happen is the carbs pull the boot out and the 'trumpet' shape creates a seal.  Trouble is, my carbs don't sit far enough away from the airbox to make that seal tight.  Maybe tight enough on 1 and 2, but I could stick a popsickle stick through the space on 4.

I have a '78 750 F2. The airbox boot "trumpets" you are referrring to on mine are pushed into the airbox and the tube part fits via a groove to the actual airbox... the trumpet part sits deep inside.... pics below. Is this what yours look like? I just purchased these new as there was one of the four of my originals that did not have the groove and was as loose as anything.... was perhaps off/for a different model?

Cheers, Phil

[Raul CB750K1]

Amen.

[gregimotis]

Regarding the pictures...

That is how mine look, and it looks like they should fit as you describe.  Thing is though, the carb is too far from the airbox for that to work - about half an inch too far.  I'll check the carb to manifold rubbers and see if that might be related.


Thanks for the help - at least now I know for sure how it's supposed to be.

[Bob Wessner]

Hmm, a half inch sort, that's quite a bit. Wouldn't account for 1/2", but one other thing I noticed on my 750 fitting airbox/carbs/rubber manifolds, in addition to making sure the manifolds to the head are oriented correctly, the same thing goes for the rubbers to airbox. I happened to notice the groove ring pointed out is not, how should I say, even all the way around. There is a slight variation but I can't recall if the narrowest part goes on top, or the bottom (get on of them out and slowly turn it to see if you notice it also). It does make a difference in a very slight angle when trying to get them to fit tightly to the carbs.

[eldar]

Are you sure they are not backwards? hey you never know, stranger things have been done!

[gregimotis]

Followup in case anyone ever has a similar issue:




The old rubbers on my original airbox had shrunk and warped enough that they no longer fit right and I couldn't see this until I installed the new boots and installed the airbox on the carbs.

With new boots, the boots sort of screw onto the airbox (as described by Mr. Wessener) and then also fit onto the carb.  By the way, getting the airbox onto the carb properly is 100X easier with the new rubber.