Topic: '74 airbox not fitting

[Thunder]

Ok hello all

well bought the bike on Fri(750 1974), and on sat got a hold of an air box, was a bit dubious because it had cb750f-f on the side but the inlet tracts look to be the right size,and i don't know of any other places locally that might have one.

Got home and pulled the PO's pods and set about "installing said air box", which incidentally , with the exception of the inlet rubbers, is identical to my 78.

Eventually got it on (hairsbreadth from a coronary ).The old rubber were ROCK hard(I soaked em in transmission stop leak, smothered in wd40 etc).heated em with a heat gun ... and it finally slipped on, but not real good.

By thor7223, shot with E71 at 2009-05-10

By thor7223, shot with E71 at 2009-05-10

By thor7223, shot with E71 at 2009-05-10


Now Are the air boxes the same (74 and 78)?
The rubbers don't seem long enough to go over the carb lips(shrunk?)

However the diameter is the same size as the carb, and when i had em off, i test fitted the inlet rubbers and the tract inside felt smooth up until and into the carb(no lip, or gap,or drop)

Please tell me the airbox is cool.
Got a left hand side cover (Aftermarket) and shocks for $40, so the day went well regardless.


Cheers again
Thor

[HondaMan]

Sorry, but the 74 and 78 boxes are not the same. 

The later carbs had different bodies, and the airbox was adjusted to fit them. It got a bigger internal volume, shorter boots, taller (and a real #$%! to install) and quieter. It did flow a little better than the K4 box, though, while remaining quieter. You can always tell them apart in a glance: the later ones have narrower "end caps" and the vent is pointing backward on the bottom, while the earlier ones have vents pointing downward and narrower ribs, wider "end caps".

If you remove the mounting screws and push the box forward, you might find that it will match up to the carbs, though. If this works, you might consider making some small brackets from sheet metal, one end bolting to the box mounts and the other to the frame mounts: paint them black for invisibility (unless you have some of that invisible paint?) and enjoy a bit of extra high-end HP for your efforts.

In the next installation, try splitting the box into its halves, install the upper first, then the lower onto the upper, if you have the necessary tools. Sometimes that helps.

[Thunder]

Thanks mate.

Yeah i did install with the half on first method.

Well i think I'm gonna make do with the box as it is, but get the correct boots (the ones for a 74)from davidsilver, this should work right, at least until i manage to find a genuine box.

[Thunder]

Just had a thought(dangerous i know) if i take the sort inlet rubbers off the pods, they can be fitted onto the carbs and siliconed to the box.

How important is the length if the tracts?

[HondaMan]

More important than the tract length is the little velocity stacks inside the Honda boots. These stacks make a noticeable performance and smoothness change to the engine. Without them, you will find a "flat spot" where it stumbles a bit because of turbulent airflow into the throat of the carb(s). For example, on a K4 with pods, there is a flat spot at about 3500 RPM that makes riders think they "have to rejet". Installing the stock airbox makes this completely disappear. If you desire more air flow, install a K&N gauze type air filter inside the stock box.

The fix for using the pods is to install slides with LESS slide cutaway, impossible to do with these bikes. 

[Duke McDukiedook]

Yeah Thunder,

Do yourself a favor and get the K&N filter. Breathes more easily and it should be the last air filter you have to buy!

[Donzon]

FWIW, I bought my '74 used, and it has the same airbox on it as yours.  Who knew

Don

[Thunder]

"For example, on a K4 with pods, there is a flat spot at about 3500 RPM that makes riders think they "have to rejet". Installing the stock airbox makes this completely disappear'

Wow, i'm speechless, i see why they call you Hondaman , the above , is exactly the symptoms the PO described when i was buying her and asked about her faults.Exactly,down to a T, 3500rpm flat spot the works... a wealth of knowledge here....

Ok, well i have the velocity stacks, and the pos fittings, i am going to see what i can come up with those two, before ordering new ones....
Going to get the KnN as well.

Now i just gotta get the carbs to stop leaking...

Tx gain fer the help