Topic: Airbox fit for '75 750f

[littlebronco]

1975 CB750f, I just went from individual pod filters that came on the bike to a stock airbox that I got on ebay.  The airbox was said to be for my year and looks exactly like all the resources I could find indicate is correct for my bike.  I managed to get it on after only a mild amount of shoving, but my concern is the fit of the boots.  I got them onto the carbs alright, and mounted the airbox to the frame.  Now if I look real close it seems there is a lip on each boot against which the airbox should rest, creating an airtight connection, but some places this isn't exactly tight to the airbox.  Is this wrong and can cause air leaks?  90% of the boot is hidden inside the airbox (the end that flanges out).  If someone has a nice close up picture of how it should look attached that would be of great help since I've never seen what it should be like.

[Gordon]

I'm not sure if this picture will help, but it's the best I've got right now.  You should have an airtight connection between the rubber boot and the air box.  Sometimes the boots just get too old and hard and need to be replaced.  Hope this helps!
Gordon

[Terry in Australia]

Loosn off the clamps and rotate your boots mate, they are all bent at different angles, but if you turn them they'll seat into your airbox and on your carbs properly. They do go hard with age though, but you can buy new ones. (and they are a bastard to fit!) Cheers, Terry.

[Bob Wessner]

Gee, I don't recall the airbox side boots being angled in any way  I know the boots, or insulators, as Honda calls them on the carb to engine connection are. It's certainly best to get a good tight fit, but a leak on the airbox side would not be as problematic as one on the carb-to-engine connections.

[MRieck]

Gee, I don't recall the airbox side boots being angled in any way  I know the boots, or insulators, as Honda calls them on the carb to engine connection are. It's certainly best to get a good tight fit, but a leak on the airbox side would not be as problematic as one on the carb-to-engine connections.

Your intake boots can be at odd angles which will generally tilt the carbs up and not allow a straight connection to the airbox boots- I think that's what Terry meant. Why Honda didn't put alignment marks on the head and boots I'll never know.

[Bob Wessner]

Ah, now I see what you mean,  good point. I must have stepped into dumb luck fitting mine, but your comment about alignment marks gives me the idea to go out and mark mine for the future.

[littlebronco]

Thanks for all the replies.  On closer inspection, the boots do have a slight angle to them.  I tried a few different orientations and the best fit was having them angled upwards.  Unfortunately to get them to seat all the way airtight against the airbox, the airbox would have to be mounted about a half-inch closer to the carbs than the brackets allow.  I think for a solution I'll try to hunt down some large rubber washers to pad the boots against the airbox. 

As for the comment about marking the orientation of the boots, I noticed the angle of the boots is symmetric with respect to a seam in the rubber.  So you can line up the rubber seam with a seam in the intake of the carb.

I really appreciate the help, guys.

[Dennis]

Yoru comment on moving the airbox 1/2" closer to the carbs is somewhat confusing.
I have a '75 CB750F,all original and unrestored and there isn't any space to move the airbox after it is installed.
Something is not correct and that is what I would be looking for

[Terry in Australia]

The trick is, I believe, to fit the rubber boots to the carbs so that they're nice and snug BEFORE installing the two 6mm securing screws for the airbox. I's a bit tricky pulling the airbox back toward the seat while trying to get the screws lined up, (particularly if persisting with old rubber boots that have shrunk and hardened over the last 30 years) but I replaced all the boots on my F2 including the carb to cylinder head boots, so they are flexible enough to allow some movement. Cheers, Terry.

[littlebronco]

In response to Dennis, all I can say is I think the boots have shrunk with time, so there is more room than there would be with new boots.  My solution was to go to the hardware store and buy o-rings for each boot that are about 3/16" in diameter width-wise and fit the circumference of the boot flange exactly.  Nice tight fit.  Then I attached the boots to carbs, then heaved a little to mount the airbox.  Definitely tighter than before and I'm hoping no air leaks, but I haven't had a chance to fire it up (dead battery at the moment).  Are there any suggestions to check for air leaks?  At this point I'm assuming the carbs will show it (cylinders running lean, hard to balance, etc).