CM91 Question(s)

jeff kjoller

New Member
Hello All-
Working on getting a CM91 restored. I removed the carb to clean and rebuild. If you reference my photo you will see two circles. One in yellow one in red.

question 1: see yellow circle. what is this port? I don't remember unhooking any hose, etc. from this when I removed the carb. Am I missing something here?

question 2: see red circle. this is the filter/cleanout area (if I understand correctly). The o-ring is worn and this is leaking fuel. I tried replacing the o-ring with one from local auto store. couldn't find the exact size so I tried one that was a little smaller and one that was a little larger. both failed. i also tried some gasket sealer. that didn't work. Any ideas of what i can do to stop the leak?

FYI, I've tried CMS (https://www.cmsnl.com/honda-motorcycles_model2/) to find part numbers and view diagrams. Nothing helped.

Thanks, Jeff
 

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wanrep

Active Member
That port is just a vent for the float bowl. It originally had a hose on it that didn't connect to anything.

What size is that o-ring that came out? Should be something like 24mm i.d. x 2.4mm.
 

jeff kjoller

New Member
Does anyone know how to solve the filter/cleanout leak?
"question 2: see red circle. this is the filter/cleanout area (if I understand correctly). The o-ring is worn and this is leaking fuel. I tried replacing the o-ring with one from local auto store. couldn't find the exact size so I tried one that was a little smaller and one that was a little larger. both failed. i also tried some gasket sealer. that didn't work. Any ideas of what i can do to stop the leak?"
 

kirrbby

Well-Known Member
There is a o-ring seal there, AND a small fiber kinda washer seal for the screw too. Did you address both??
 

jeff kjoller

New Member
yes. the fiber washer used on the screw is new. I can see it is not leaking there. Its coming out from the edge of the cap. As I said previously, I don't have a replacement o-ring. So I bought some various sizes from local auto store. The closest in size were a bit too small or a bit too large (I tried both and they leaked). When I look at a parts catalog, there is no part number for this o-ring.
 

jeff kjoller

New Member
An update for anyone interested: the carb rebuild kit you can buy online does not provide any o-ring for the filter/cleanout area. It does show a paper one but that is too small and doesn't work. Buying an 18.6 o-ring online to see if that will work
 

clk4robotics

New Member
Hi,
New to this forum, I made an account specifically to ask for help with this exact problem. I was hoping somebody could tell me the o-ring size for this exact carburetor. I’m having a hard time finding an o-ring to fit the carburetor screen port. I have a 60’s Honda cm91, with the m91a carb? Not sure of the year, maybe somebody here could tell me how to determine this? I appreciate any help and thank you for your time in advance. Sorry for bumping an older thread, I’m amateur at best with online forums.

-Chuck
 

kirrbby

Well-Known Member
I'm thinking it might be the 18.6x1.7mm size. Maybe try to get a idea of the size by measuring your carb...for comparison, before you buy.

Screenshot_20231216-201422.png
Screenshot_20231216-201447.png
 

clk4robotics

New Member
Thank you for the replies. I checked the parts diagram and verified the part number. I ordered an 18.6mm from dratv on eBay, will update when it comes, if this resolved the issue. I apologize for the delayed response, I’ve been extremely ill.

Thank you,
Chuck
 

clk4robotics

New Member
The 18.6x2mm o-ring fit and worked perfectly, but now I need to find a replacement for the small red one that goes between the screw head and the cap. When I tightened the screw/bolt down it squeezed and separated the fibrous red washer? Can anybody tell me how to determine the year of my bike? Thank you for the help, it brought resolution to many weeks of trial and error.

-Chuck
 

kirrbby

Well-Known Member
The only place that I've seen the little red washers is when they are part of a rebuild kit...Keyster kit maybe. I wonder if you could cut a piece of gasket material to work..?
 

clk4robotics

New Member
The only place that I've seen the little red washers is when they are part of a rebuild kit...Keyster kit maybe. I wonder if you could cut a piece of gasket material to work..?
Yea I’ve seen the kits, for about $30 online. At that price, it makes more sense to purchase a newer aftermarket carburetor, if i’m unable to affordably source the “o-ring”. Can someone please give me your opinion on the matter if/what you’ve swapped in, and how it worked out? Thank you

-Chuck
 
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