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Discussion Starter #1
Hello
I bought a 90 ninja zx750f4 (or 750R) with keihin carbs about a month ago not running. I was told by former owner that the valve clearance was checked last summer and that bike sat over winter. I replaced spark plugs, had gas tank cleaned out, replaced fuel filter, replaced air filter, changed oil, changed clutch fluid, completely cleaned carbs ( jets and needles included), I am not sure if it needed all of that but I felt it was a good idea to replace anyways. I had taken the airbox off when removing carbs for cleaning and after cleaning the bike was running good except at 4 or 5k rpms it would start to run bad from sucking in too much air. Gas was also leaking out of #1 carb. I fixed float level in that carb and got it to stop leaking. After that I took the bike out for a ride around the block and it was running good but was a little sluggish on acceleration. Talked to a guy at the local bike shop and and he said the carbs were probably out of sync. I hooked up homemade syncing tool and he was right. As I was syncing the bike just died. I did a bench sync and now the bike will only run when choke is on and it revs way up to 6 or 7k and if i lower the choke the bike dies. I did manage to get it running for a couple minutes and it seemed good so I shut off the bike and reinstalled airbox to eliminate that from the problem. After reassembling airbox and putting gas tank on the problem of running only on choke has come back. Any help getting my bike to run again would be greatly appreciated.
 

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Quinton Phuckin Tarantino
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Was there crap in the gas tank ? A lot of times you can clean a set of carbs only to have to do it over when you run gas out of a dirty tank . If that is still ok the. It's time to make sure all of the passages are clean on the carbs. Use compressed air to blow the passages out and check flow . Next what are your idle mixture screws set at ?
 

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Discussion Starter #3 (Edited)
I had gas tank cleaned out and rust removed before putting the tank on. As I stated it was running fine other than the airbox being off and it getting to much air. It is just after trying to sync the carbs that the bike stopped running. Have idle screw barely turned up and I keep resetting it every time I turn the screw so I have a starting point. There is no air/fuel mixture screw so I can't adjust that. I took the spark plugs out about an hour ago and they were a little soot covered leading me to believe it is running a little rich right now but not bad enough to keep it from running.
 

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Quinton Phuckin Tarantino
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There are idle mix screws they put aluminum plugs in them so people don't mess with them from the factory . These will have to be drilled out . On a kei-hein carb they are right next to the float bowl aimed downward . Something is causing a lean mixture in at least one or two cylinders this is why your idle hangs high sometimes And why it won't idle other times. Look for vacuum leaks ie bad manifolds or missing vacuum lines etc .
 

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Discussion Starter #5
Problem fixed. I got the bike to start lowered the choke as much as I could without it dying and played with the screws for syncing. After I got it to warm up I synced the carbs best I could. Bike runs great and pulls really hard no more issues that I know of. Thank you for the help anyways.
 

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wtf is a bench sync? Where you take the carbs out and then eyeball it?

You can't sync carbs that way lol...

Where in wisconsin are you? If you are anywhere near racine I would be more than happy to help you out with this kind of stuff.

And a big concern in whether or not the bike will start is the idle control screw (basically controls how far open the butterflies are at idle)... If that is too far open or totally closed the bike may never start at all. That is the first thing I try when starting a bike that I just took the carbs off of.
 

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You can do a mechanical sync but it's never close. Usually enough to keep the bike running, but always at least 3" of vacuum off.
 
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