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Motor stalls with choke off

Chamutti

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Hi all, I just got a cafe style 77 CB750 with a 78 motor. It's got a shorty 4 into 1 pipe on it, overall the bike looks and sounds great but at the moment I've got a problem, well I'm sure there's more than just one. FYI: I'm relatively new to working on bikes and I've never worked on anything with more than 1 cylinder.

She stalls out completely when the choke is pushed in. Even if she has been warmed up a bit, as soon as I push the choke in she dies. I have no idea if it has been re-jetted or not. I have no idea what has been done to it as the previous owner bought it from the person that did the work. She starts right up with it out, I mean starts right up immediately. There is an issue with the choke as well, I've had to rig the choke to keep it out as it wants to suck back in if not being held out by something.

Any idea where to start? Thanks in advance for the help, let me know if you need any more info.



Black beast.jpg
 
it sounds like something is plugged in the fuel circuit. I would pull the carbs and give them a good cleaning and look at the jet size once you pull it apart for a start.Check your plugs and see what color they are burning.They should be a tan color.Im sure some of our experts will chime in soon with more advice.
 
It very well could have some plug idle jets or passges. Also, just something to think about would be to check the base idle screw. It could be possible that the idle is set too low, the choke has a fast idle setup that increases idle speed when the choke is closed and decreases it back to base idle when it is opened. It is possible the idle speed screw is set too low or backed out too far that it isn't even touching the idle stop. The choke on these carbs is designed to be spring loaded to the full open position. It sounds to me like the spring for the choke is installed wrong or maybe even gone. It should by default spring to the open position.
 
[I would also start by cleaning the carbs. A plugged pilot jet will cause it not to idle. Then have all the carb settings adjusted to spec. As far as the choke goes there must be something missing it should stay on by it self. Being new to carb work I would get a good manual and follow it. These carbs are not very complicated but it doesn't take long to get them monkeyed up especially the synchronization.
 
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