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1978 CB400A stockish
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83 Posts
Discussion Starter #1 (Edited)
Here’s a video I made of what is going on with the bike. It will start and idle. It’s able to start using the choke when cold and will idle when no choke is used after. When you give it fuel it doesn’t rev freely and is erratic. It will die when coming off full throttle. Once it’s warm if you start it using the choke it is very erratic. Idle/air screws are out 1 3/4 turns. I haven’t set the idle at 1250 because I don’t have a tach or a multimeter that has that function.

I was getting a rich condition on the right side but after I bench synced the carbs they are even but now erratic. I’m thinking maybe something got into the carbs and is blocking a passageway or jet. I need to pull them off to verify the jet sizes again. The floats are at 15.5mm.

Steve Dot World CB400A rpm/throttle issues
 

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Registered
1978 CB400A stockish
Joined
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83 Posts
Discussion Starter #2
I just tore into my carbs again. So the right side air/fuel adjustment screw is damaged and the needle is broken off and lodged in the 4mm long orifice. Wish me luck in its extraction.
 

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Registered
1978 CB400A stockish
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83 Posts
Discussion Starter #3 (Edited)
I used some heat from a heat gun, liquid wrench, a sewing needle I snipped the end off held by pliers, and some choice words. It finally popped out. I realized that my main jet and secondary jet in the left carb were switched (110main/70sec).

I got the jets in the correct spots (70 main/110 sec), put the pilot jets back in (although one has the tip missing), everything back on and fired it back up.

Choke on had some sputtering. Then smoothed out. Choke pushed in, idled low. Tried to raise idle up and didn’t change until I got pretty far in and it died. Tried to give it throttle after backing the idle screw back out to just after contact and it dies when tipped in every time. Adjusting the idle screw in does nothing.

I’m going to order some new pilot screws to replace the one that was snapped off.

EDIT: I actually found one that I took off, replaced it after cleaning it up and now I’m super rich and I still can’t adjust the idle unless the choke is out. I think the idle circuit is clogged because the choke would bypass that when applied.
 

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Registered
1978 CB400A stockish
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83 Posts
Discussion Starter #4
I ended up taking the carbs off again and blowing everything out with carb cleaner and air. All the passageways are now cleaned out again. I got some fresh fuel and dropped a smidge of fuel system cleaner in for good measure.

The bike idles rough but once you get past tip in it revs nice. You can adjust the idle again now. I’m gonna call it mostly fixed and rideable.
 
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