Topic: Missing part in carb ( help!! )

[bluesmoke69]

Brass part is missing is carb junk?? Picture is hard to see but if you look at hondaman's picture. One of the brass thing that he has the wire in is missing WTF!! Any help would be great.

[HondaMan]

It's a little hard to tell from your picture: what model carb is that? If it is a 7A series, there might not be vent reduction inserts in the 2 center carbs of the rack. The 7A were found on the very last K6 and the F0 bikes.

[bluesmoke69]

Carbs are from 1976 CB750F I know picture is bad the hole I am talking about is where you have the wire to clean passage. On your photo there are two of them. On my other carbs there are two of them as well. On this carb there is only one will try to get better picture to night. Carb was on the #1 or #4 cylinder I will have to check.Thanks for your help.

[bluesmoke69]

Is it possible the PO switched the two set of carbs and does it make a difference the order of the carbs. Thank for any help.

[KingCustomCycles.com]

Those are vent orifices, some have them and some don't.  This was covered in a post last week, "search"

[CycleRanger]

It's a little hard to tell from your picture: what model carb is that? If it is a 7A series, there might not be vent reduction inserts in the 2 center carbs of the rack. The 7A were found on the very last K6 and the F0 bikes.

Actually, it was my understanding that the 7A carbs were used on the K1 & 2's and the K6's used the 086A's. (I can't speak for the F0.)
(And the 657A & B were used K3-K5.)
I ask because I believe you quoted the same thing regarding 7A use in your book and I was wondering.

[VTCBike750]

So I had this Monday from my 72's carbs (657A). 
http://forums.sohc4.net/index.php?topic=93021.0



The posts Ive been able to find talk about the #1 and 4 carbs only having 1 brass insert.  But this is my #2.  My #3 has 2 inserts. 

[HondaMan]

It's a little hard to tell from your picture: what model carb is that? If it is a 7A series, there might not be vent reduction inserts in the 2 center carbs of the rack. The 7A were found on the very last K6 and the F0 bikes.

Actually, it was my understanding that the 7A carbs were used on the K1 & 2's and the K6's used the 086A's. (I can't speak for the F0.)
(And the 657A & B were used K3-K5.)
I ask because I believe you quoted the same thing regarding 7A use in your book and I was wondering.

There are more 7A carbs on the F0 than on any others I know about. Most of the K1 ended up with 657A carbs with #27201 needles and 110 mainjets, with the needles in the 4th clip slot, or some clipped in slot #3, with 115 mains. All my notes from those days showed the last of the 657A on the last K1 bikes (hence the description in the book). The 7A has the thicker #27301 needle, which is the emissions control lean-out for the lower RPM range up to 3000 RPM (that was the official test in those days), after which (1/3 throttle) it tapers quicker to meet up with the later-opening cam. That's what gives the F bikes that 'rush' feeling they have at about 6500 RPM, more than the earlier bikes: they are a little too lean in the lower RPM ranges. On the good side: they fouled plugs much less with the older fuels when calibrated this way.

[HondaMan]

Is it possible the PO switched the two set of carbs and does it make a difference the order of the carbs. Thank for any help.

Could that particular hole be one of the ones going up to the vent hose? Those may not have the brass orifice(s) at all.

[CycleRanger]

There are more 7A carbs on the F0 than on any others I know about. Most of the K1 ended up with 657A carbs with #27201 needles and 110 mainjets, with the needles in the 4th clip slot, or some clipped in slot #3, with 115 mains. All my notes from those days showed the last of the 657A on the last K1 bikes (hence the description in the book). The 7A has the thicker #27301 needle, which is the emissions control lean-out for the lower RPM range up to 3000 RPM (that was the official test in those days), after which (1/3 throttle) it tapers quicker to meet up with the later-opening cam. That's what gives the F bikes that 'rush' feeling they have at about 6500 RPM, more than the earlier bikes: they are a little too lean in the lower RPM ranges. On the good side: they fouled plugs much less with the older fuels when calibrated this way.

Huh, ok. Thanks! 

[bluesmoke69]

Mark mine look like VTC carb one brass with a hole in the center nothing in the other. Two carb like that and the other two have the brass with holes in center. My question which position should the one with only one bass/ no brass be in. I believe you said 2 and 3 cylinders? Thanks for all you help.

[HondaMan]

Mark mine look like VTC carb one brass with a hole in the center nothing in the other. Two carb like that and the other two have the brass with holes in center. My question which position should the one with only one bass/ no brass be in. I believe you said 2 and 3 cylinders? Thanks for all you help.

This is wierd...I wrote back to this last week, but the post is missing. (?)

Check on the top side of the mystery carb to see if it is one with the little fitting for the breather tube that goes vertical. The 2 center carbs will have this fitting for the tubes, which should go vertical to the frame, then back along the frame tubes to the top of the airbox. In the post-1976 airbox, these actually plug into the top of the box. On earlier engines they vent to atmosphere under the seat. For an improved (deeper) float bowl level at highway speeds, plugging them into the airbox will raise the bowl levels about 1mm by improving the airflow through the bowls.