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Discussion Starter · #1 ·
I've been fixing up a 1978 CB400T. I got the bike from my grandpa and he always had starting issues with the bike. I have taken the carbs apart, cleaned them and replaced the jets. after cleaning the carb and replacing the jets I still have starting issues. I choke the bike and and it starts, but instantly dies. I have to do that a couple times in a row before it idles for a few seconds and dies. After a while of starting it and it dying it'll finally run. It will not start if I try to give it gas while trying to start it. Once I get the bike to stay on while idling, i will try to give it a little gas to rev it up but the engine will go from 1000 rpm to like 400rpm and almost die. After I try to give it gas and it Boggs down I will stopping giving it gas and the engine will rev up well above 2000 rpms after I let the throttle retreat to the idle position. I have to let the engine warm up before the engine will actually rev up when I give it gas. Once I run the bike for a while and it warms up the idling stays around 1200-1300 rpms and the engine runs well and responds much to the throttle.

Does anyone know what the issue could be? The engine is almost 40 years old but it also only has about 4800 miles on it, so maybe it's just an old engine problem. Any help is greatly appreciated.

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Discussion Starter · #3 ·
I will have to check the ignition system. I did replace the spark plugs with the NGK D8EA. I have not done a compression test.

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As above, If your spark and compression is good, then concentrate on the carbs and inlet boots. My carbs took a few cleans (by hand/ carb spray and ultrasonic) before they were right. It's quite likely that the rings have worn or a valve or two is gummed up and not sealing. If you can rebuild a carb, you can rebuild the top end. It's not as hard as an exploded view looks! :)
 
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