Help ID'ing jets

Losmanja

Losmanja

New Member
To start, Im not looking to the correct jet sizes, etc. Im ok with the trial and error method of tuning. The problem is that I dont know which jet does what, and also my carb refers to a primary main jet and a secondary main jet and a slow jet? I have two main jets and one slow?

Here is the diagram of the carb.

1980 Honda CM400t
carb.jpg


Now here is what I pulled from the carb. The numbers in parenthesis refer to the carb diagram above. The others are the jet sizes that are currently in the carb.
jets.jpg


My issues are as follows:

1. If the main jet controls wide open throttle, then why do I have two main jets? Which do I change?
2. The (27) jet I assumed was my slow jet because it had a 72 size jet in it. Well then what is the (32) slow jet?
3. I can easily purchase small jets for the (33) and (27) styles, however I cant find anything that looks like (32).

Any clarification or help would be greatly appreciated.
 
I think youre correct. I could be wrong but i think 33 is your mainjet and 27 is the slowjet in common terms. Honda manuals sometimes are kinda weird when they talk about the carbs. 27 screws into the top of 26, right? I think 32 and 26 would more commonly be called the mainjet holder and needle(slow) jet holder. For whatever reason sometimes honda decides to make up their own names. Theres probably a good reason behind it, engineering wise, but it confuses the hell out of normal people.

I could be wrong though so maybe wait and see what other people have to say.
 
in your picture starting at the top left thats the main jet next to that is your secondary main jet.
now in the bottom left that is what your main jet screws in to and what the needle slides threw. on the bottom right of the pic is your slow jet. try to read what your looking for confused me. depending what your trying to fine tune depends on what jet you need to change.
 
Primary main (27) feeds pilot jet, which has a rubber plug. and shouldn't be connected directly to fuel in float bowl
secondary main (33) is the one you change
You are going to have problems because needle isn't adjustable and it will run too rich mid range when it's jetted properly for flat out.
Needle needs to drop to lean out mid range.
It really is one of the bikes that will run better with stock airbox

PJ
 
Thanks for the responses. I knew that it would run better with the box, but I thought I could take some time and tune it properly by adjusting the jets. Are you saying that its not worth the effort since its a fixed pin? Un-tunable? Would diff carbs do the trick?

I kept the airbox as a backup, however Id really prefer to tough out a solution and avoid using it.
 
I actually have it running pretty solid. I've tuned it to the best of my ability but now the only thing that I cant figure out is how to get rid of a bubbling sound. Left cylinder runs strong and steady. Right cylinder had a little irregularity and a bubbling sound out of the pipe. I cant seem to get this cylinder as steady as the left. Im not sure what that bubbling sound is an indicator of.
 
Bubbling...can you post an audio file or a video? Hmmm...

Could be anything from improper ignition (plugs/leads/coil) to a worn vlave seat IMO.

- boingk
 
Carbs massively out of sync.
You running open pipe (or bar through baffles?)

PJ
 
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