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Discussion Starter #1
Recently picked up a CB350 in pretty rough condition. Put new rubber in the carbs timed the ignition, adjusted the valve clearances and found that it has good compression. When the whole thing is back together I can only get one cylinder to burn, the left side pipe is dead cold. I switched the spark plugs and checked ignition and all of that looks good.

I had a spare carb (doesn't match so I don't want to really use it permanently) that I threw on the left cylinder, and boom, it light right up. So clearly the problem is my original carb. I check the jets and they all look clear, the diaphragm is fine and all the rubber is new. Throttle cable connection is fine too.

What can I do to check that I can get fuel through the original left side carburetor? On other bikes I would have synced them with a manometer, but there is no where to do this on this bike. Any thoughts would be appreciated. Thanks!
 

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The jets can be clear, but the passages in the carb blocked and the emulsifiers blocked. There are pressed in parts of the carb that should be removed and cleaned. Float level has a big effect too.
 

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Are you referring to the passages that flow around the venturi through the carburetor body? Is that as simple as just spraying some carb cleaner through them?
 

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This image is of a 450 DOHC carb, but the 350 carb has similar parts. Richard is talking about Item 10 for the main jet and SJ for the slow jet. These emulsify the air into the fuel to provide complete atomization of the fuel. They have tiny holes. I use steel guitar to clean them. That is about the smallest stiff wire I have found.

CB450 Carb.jpg
 

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Thanks for the replies! Just took the carburetor off and verified that I can see a light through the main jet and pilot jet. I also blew through the both jets and could feel air coming out of the other side of the passage (with a significant amount of resistance, but the passage is small). I've verified that the diaphragm actuates when I blow into the holes that are on the intake side of the carburetor (these are keihin 3D carbs).

I put the carb back on the bike and verified that there is fuel in the bowl by unscrewing the drain plug until I got a few drips. Started it up and the left cylinder is still very cold. I've already ruled out ignition and compression (original post). I was trying to run with choke on just now, so the problem at least effects the idle circuit.

How would float levels affect this? That's about the only part I have not touched yet. I've never had to troubleshoot carbs like this so any additional ideas would be appreciated! Thanks guys.
 

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spray starter fluid in the mouth of the carb on the side that isn't firing.

if it starts running on the starter fluid the carb is your issue.

if it still doesnt' run you have an electrical problem

90% of all "carb" problems are electrical.
 

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Thanks for the suggestions, thought I'd follow up:

The motor is running on both cylinders now, turns or the issue was that carbs were simply not cleaned well the first time (stupid I know). The carb that was giving me issues would meter fuel at an open throttle position, so I took it off and cleaned out the idle passage with a generous amount of carb cleaner. I guess this just reiterates basic carburetor maintenance on these older machines. I hope this keeps someone else from pulling their hair out over something like this.
 
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