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I’m about 6 weeks into the resurrection of my 1981 CM400T. I’ve had the bike running and even logged a few miles. How that I know what I’ve got, I’ll start going through things. For the last couple of weeks I’ve been focusing on the tank and carbs. I reinstalled everything today with the plans of firing it up. Shortly after opening the petcock, i get fuel running out all the over flows; talk about a kick in the teeth. Dreading the thought of pulling the carbs back off, I spend the next 15 minutes stewing on it. Knowing that the bowls are full, I attempt to start the bike for the nuts of. After a few attempts, it fires up and runs great until it runs out of fuel. I spend the next few minutes opening and closing the petcock to keep it fueled. After running for awhile I notice I’m getting less and less out of the overflow. As I continue doing this I’m also tapping on the carbs. After a short period no more overflow. I’ve run the bike several times since with no leakage; running great. The carbs were sitting on my work bench for the last week. Is it possible that the floats were stuck in the open position and simply needed a chance to work free or should I be looking for an underlying issue? I cleaned the carbs with Pinesol, maybe that was too sticky.

C
 

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It may be dirt/rust working through,do you have your in tank screen/filter in place? and a dose of marvel mystery oil/sea foam hurts. any pictures?
 

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May not be your problem but on a set of cb350 carbs I rebuilt the floats were a fraction to wide and were hitting the side of the carbs. I pinched them together a little and they were fine. May not be your problem but wouldnt hurt to look.

Just a thought.

Bill
 

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Curious what running issues did you have and how did you finally realize the floats were too wide?

As for the OP, I would guess crud is the issue.
Remove the tank and petcock to see if it's plugged.
You can drop the float bowls with the carbs on the bike. Check for debris in the bowls and reclean the float valve and seat contact areas


May not be your problem but on a set of cb350 carbs I rebuilt the floats were a fraction to wide and were hitting the side of the carbs. I pinched them together a little and they were fine. May not be your problem but wouldnt hurt to look.

Just a thought.

Bill
 

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When I swapped the engine on my '82 cb450sc the carbs did this after I installed them. I took a big screwdriver and banged the carb bodies and the floats dropped.
 

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The float needles tend to stick in their seat bores at times when left dry, not sure of the reason other than old fuel deposits. That's why I sand/polish the 4 ribs on each needle before installing as well as polishing the bore.
 

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Hi doode. The carbs overflowed after being reinstalled. Removed and checked every thing could find nothing wrong. checking float level and noticed float sticking .Found float just touching side of carb. Motor was brought to me non running. Dont know what if anything the PO did to it.

Bill

After thought. As you know the floats will move a small amount on the rod they are mounted on. I think the floats were just wide enough to work part of the time and not work part of the time depending on how they shifted on the rod. Anyway moving them closer together fixed the problem.


Bill
 
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