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Discussion Starter · #1 ·
My sons Green '72 CB 350 has recently decided to start running rough.
Mixed High/Low idle, general lack of response.

Checked - & Re-Checked timing. All Good.
No Points-Condenser to check - Charlie's Place Electronic Ignition.

Valves sound good not over loud normal clicking, same as my Red One.

OK - CARBS - let's take a look see.

Sure enough -Right side has a tear in the diaphragm.
Good - Now we know how to fix things.

BUT ... CHOICES:

JBM - Has replacements that require cutting off the Plastic Retainer Rings on the slide.
It has an extra FAT/Thick Center Section that fills the space where the rings were. - No Alignment Tab.
Looks pretty easy to install.
Diagonal Cutters Snip off the Plastic top/bottom retainer rings.
Stretch new diaphragm into place.
Line up Slide Holes with Carb Body
Drop Slide into Carb - done.
Assume the Fat Center Section has enough friction to prevent slide from rotating.
No alignment Tab so assume friction of top cover prevent any diaphragm rotation.
Once the Plastic Rings are cut off they are gone for good. Good/Bad ?

4into1 - has direct OEM replacement Type diaphragms.
Standard Alignment Tab in the Top Ring.
Lots of Use Caution and Be Careful pressing the new diaphragm into the old slot space between the Plastic Retainer Rings.

So... here's the question.
Anybody here have experience with either or both of these replacement parts?

I've rebuilt plenty of CV Carbs, I've heard about torn diaphragms. I've just been lucky and not had to deal with it until now.

If you have used either one:
What did you like about them
What did you NOT like?
 

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Yendor - I went the JMB way and it was super easy. Clipping off the plastic was not difficult at all.

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Discussion Starter · #3 ·
Thank You.

As I said I've rebuilt multiple CV 722a's but have been lucky enough to had not had to deal with the diaphragms.
 

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Yendor - I went the JMB way and it was super easy. Clipping off the plastic was not difficult at all.

View attachment 191089
View attachment 191097
I agree with ScramblerCurtis the JMB is easy enough and it feels very secure. the thick rubber part is not looser than the OEM assembly or anything like that.

One question for ScamblerCurtis, though, is whether you remove the rubber gasket as well as the plastic. I ask because it looks like the diaphragm is not fully seated in the first photo, right side. After cutting and removing the plastic, there is also a very thin black rubber gasket in the groove. I removed that thinking the jMB, being rubber itself, didn't need another gasket. After doing so. The top and bottom of the thick part of the JMB seats fully into the groove.
 

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I"ve used the jmb ones as well. great product and easy to install.

I however prefer to find NOS Honda slides...I just like having the alignment dimple so I don't forget to align them when servicing.
 

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I agree with ScramblerCurtis the JMB is easy enough and it feels very secure. the thick rubber part is not looser than the OEM assembly or anything like that.

One question for ScamblerCurtis, though, is whether you remove the rubber gasket as well as the plastic. I ask because it looks like the diaphragm is not fully seated in the first photo, right side. After cutting and removing the plastic, there is also a very thin black rubber gasket in the groove. I removed that thinking the jMB, being rubber itself, didn't need another gasket. After doing so. The top and bottom of the thick part of the JMB seats fully into the groove.
As I remember you remove everything on the slide - plastic ring and rubber seal. The picture may not look as though it is completely seated.
 

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Here's a question that comes to mind, since I replaced my diaphragms/slides with OEM ones that came complete with the drop-in needles. Are the needles the same for every era of 350 carb? I left the new ones in place instead of using my old ones (which looked a bit worn), but I have no idea which model of 350 carb the new ones were meant for. The slides were identical to the ones in my 3D carbs, and the bike runs fine, but is a bit rich.
 

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Yendor. I have a parts carb I can check and see if the slide and diaphragm are in good condition. If they are I would be willing to ship it to you.
 

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Discussion Starter · #10 ·
Thanks for the offer Harsh, but save it for someone who might need it in the future.
(I actually have about 3 complete sets of carbs(various models).
( I'm in the middle of rebuilding another set of 350 C's) - These are taking some time as the Brass Parts had been abused.

But... I had already ordered and installed the JBM Diaphragms.

I was just waiting to get a decent chunk of time to do a few additional tasks before re-installing the carbs.
While I the Carbs are off it's real easy to get access to the Intake Valves and the Cam Chain Tensioner.
So I did a full Valve Adjustment yesterday before re-installing the carbs.

Everything went back in real nice and simple. - I re-set the Throttle Cable Sync, and the bike fired right up.

A simple Idle Mix & Speed adjustment and off we went for a test run. (with my son following on my Red Bike)
It pulls real smooth throughout the full RPM Range.
I tend to shift at about 6-7K and it felt strong all the way.

I turned it back over to my son and he is very pleased to say the least.
 
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