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1981 Honda CM400C Custom
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Discussion Starter · #1 ·
Hello all,
About a year ago I bought a 1981 Honda CM400C Custom. It was advertised as turned over but did not run, and the seller said it would most likely need a carb cleaning it should be good. Having never ridden a motorcycle or done any kind of mechanic work, I decided to go for it, and it has apparently taken me a year to wonder if I am cut out for this.
I removed the carb after much trouble and cleaned/replaced all the essential parts. From there, I threw it back in, replaced the battery and the sparkplugs, added new fuel, and still nothing. I'm really stuck with what to do, I don't even think that there is fuel getting to the carbs, but all of my lines are clear. I can't unscrew (what I think) the carb drain screws, as they are so stripped they are totally unscrewable. I have begun to search for a new carb entirely, but many of them cost as much as I paid for the bike itself.

Does anyone have any suggestions for me, I am totally unsure what else I can do here and am afraid to say that I'm about ready to give up.
 

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Does gas run out of the hose, when it is pulled loose from the carburetor? Pull off the air cleaners and spray a small amount of gas into the carb throats, does it try to run then?
 

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1981 Honda CM400C Custom
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Discussion Starter · #4 ·
Does gas run out of the hose, when it is pulled loose from the carburetor? Pull off the air cleaners and spray a small amount of gas into the carb throats, does it try to run then?
Gas does run out of the hose when pulled loose, and when I spray gas/ether/carb cleaner through the air intake it does run until it is burned off.
 

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Hey Miles, welcome to the list. The good news is , it sounds like your bike has spark. The bad, it sounds like your carbs are not thoroughly clean. The info you need to correctly rebuild your carbs can be found in the SOHC Fuel and Carburation section of this forum . Read this write up back and forth, to see what your dealing with. It will take patience and a methodical approach to clean/rebuild the carbs. I'm guessing they got pretty gummed up and dirty during the previous owners ownership. Understand these Keihin carbs, many times will not "clean up" just by removing jets and spraying a can of carb clean thru them, many of the orfices are very small, and in this age of e10 gasoline, will require more effort/ different approach to successfully clean/clear them, which usually involves disassembling and separating them. Realize the left carb feeds gas to the right carb. This is not something you, or anyone else, is going to complete in a days time . An ultrasonic jewelry cleaner works well for the cleaning aspect. Again, read LDRs' carb write up . Hth, garjo
 

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I should add, don't be tempted to buy some cheap brand new carb(or carb repair kits) off of ebay as a quick fix, they will cause more problems than they fix, use fortitude in combination with oem parts only , garjo
 

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As above, and the CMSNL.com/partzilla exploded views.

The record for removing/refitting troublesome carbs of this type must be 15 times or so by now, but that was before the age of cheap ultra sonic cleaners.

My record was 5 times, pita pita pita !!!!!

I don't have an ultra sonic one so rely on initial carb outside cleaning, then stripping down carbs as much as possible but leaving butterflies in.

I arrange a container so carbs can be left totally submerged for some days in a strong redex/petrol solution. I add clean bits and bobs to take up volume and save on solution. Solution is like cherryaid at first but turns to coke. The container is covered and stored safely due to fire risk.

Airline and compressed air, carb cleaner, even a pumped oil can at times to blow out solution etc..

A final soak in fresh solution then final blow out.

Think about suitable Allan bolts for the float chambers, makes life so much easier later when carbs can be easily cleaned and blown thru in situe.

Remember clean carbs means starting at the tank fuel filler cap.

You know of the small vw type fuel filter ? Magnetic filters are available these days, as are fuel taps with sediment/crap traps which will also accommodate a small magnet.

Enjoy.....

Ps, I have seen threads about split float chamber overflow tubes, the brass tubes that stick up in the chamber. This seems to have happened after an ultrasonic session. I wonder it this is due to organ pipe effect and the frequency of the cleaner possibly ?
 

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I like NAPA carb cleaner but dont get in a hurry .Some of the passages are very small and I have left the carbs in the container for several days at a time. I buy carb kits from Sirius Consolidated . They have the correct parts made in Japan and are complete kits. They are not cheap .The last set I bought were for a 81 CM 400 A and cost about $ 75.00. Bad thing about Sirius is they sell hundreds of kits and they are not in any order. You may go through 10-15 pages before you find yours. As stated follow LDRs carb rebuild instructions.

Bill H
 

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1981 Honda CM400C Custom
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Discussion Starter · #10 ·
Hey Miles, welcome to the list. The good news is , it sounds like your bike has spark. The bad, it sounds like your carbs are not thoroughly clean. The info you need to correctly rebuild your carbs can be found in the SOHC Fuel and Carburation section of this forum . Read this write up back and forth, to see what your dealing with. It will take patience and a methodical approach to clean/rebuild the carbs. I'm guessing they got pretty gummed up and dirty during the previous owners ownership. Understand these Keihin carbs, many times will not "clean up" just by removing jets and spraying a can of carb clean thru them, many of the orfices are very small, and in this age of e10 gasoline, will require more effort/ different approach to successfully clean/clear them, which usually involves disassembling and separating them. Realize the left carb feeds gas to the right carb. This is not something you, or anyone else, is going to complete in a days time . An ultrasonic jewelry cleaner works well for the cleaning aspect. Again, read LDRs' carb write up . Hth, garjo
Thank you for the advice, man. I am looking for ultrasonic cleaners now, do you think that a 2-liter one will work, or should I get a 6-liter?
 

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Mine was supposed to be a rebuilt set but the floats were installed upside down wrong kit I suppose I got left working with an old needle I had and both sides running great now except the right side needle needs cleaned or replaced but I can test ride it by shutting off fuel till it gets low ,been pretty sick lately going to fix right needle when and if I recover but mine is 81 hondamatic 400A.good luck
 
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