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Author Topic: 1978 cb750f air box compatability  (Read 681 times)

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Offline Jake750

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1978 cb750f air box compatability
« on: October 04, 2019, 11:29:24 AM »
1978 cb750f, barn find. It didn't come with an air box, I wasn't too concerned though since I planned on running pod filters or something anyway. HOWEVER, after some research I thought it would be best to use a stock airbox. Only problem is I cannot seem to track down a 78 cb750f airbox.

Does anyone know if other cb models use the same box? Or a website I could find one for sale? Google and Ebay were to no avail.

Thanks!
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Offline Bankerdanny

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Re: 1978 cb750f air box compatability
« Reply #1 on: October 04, 2019, 11:43:58 AM »
I think that the basic box is the same between the various models and that the difference is in the rubber velocity stack/connectors between the box and the carbs. The 77-78 F model airbox uses a slightly different method of clamping the two halves together, but I don't think the shape of the box is different.

A quick check at CSMNL shows that the 77/78 K, F, and A all use the same airbox assembly and I still think that the one from an older K or F model will also work if you get the right carb rubbers.
« Last Edit: October 04, 2019, 11:51:03 AM by Bankerdanny »
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Offline Tracksnblades1

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Re: 1978 cb750f air box compatability
« Reply #2 on: October 04, 2019, 01:34:50 PM »
I think Danny may be right, however I don't have any airboxes older than 75. I haven't check part numbers either.

The later ones 77-78 had different carbs pd with accelerator pumps. 77-78 had different rubber manifolds to cylinder head also.

I have a 77f air box off right now if you need to compare the OEM rubber velocity stacks that complete the seal.
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Offline PGF550F

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Re: 1978 cb750f air box compatability
« Reply #3 on: October 04, 2019, 05:35:22 PM »
The air boxes were different for round top carbs vs PD carbs. The identified on the PD version of the air box is that it says HM CB750F-F and has the hose fitting on the center of the top half of the air box.
The PD airbox cannot be used with round top carbs, as the openings where the carb boots are is larger (49mm) vs 43mm openings on an airbox for the round top carbs.

http://forums.sohc4.net/index.php/topic,162566.msg1869016.html#msg1869016

You just have to match up the right airbox to your carburetors. I believe that the  2 different styles are dimensionally the same other than the carb boot openings.

I hope that helps, good luck


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