Honda Twins banner

1 - 7 of 7 Posts

·
Registered
Joined
·
20 Posts
Discussion Starter #1
OK, really need some advice with the carbs. CB400a starts up but roughly... running on all stock carb parts too. Pulled the plug wires one at a time and it's only running on the right cylinder. Tried to start on the left only and with the idle screw fully closed it'll sputter every couple seconds. No sputter if I give it throttle. Drips fuel from the right pipe too. I pulled the carbs and swapped all the parts I could, screwed the idle screws in all the way on both, swapped the plugs side to side and put it all back. No change! Still runs on the right cyl only. And still both idle screws are closed! What could cause them BOTH to run so incredibly rich? I did swap to the pods with a 3" extension but otherwise nothing.

Please any advice would be appreciated!! Anyone know a good old-school bike guy in western CT that could help me?!?

Thanks in advance.
Brad
 

·
Registered
Joined
·
2,756 Posts
Is the left hand spark plug wet or dry? Did you try new spark plugs? How does it run with the air cleaners removed?
 

·
Registered
Joined
·
20 Posts
Discussion Starter #3
The left plug was wet (dripping gas from the exhaust). Haven't tried new plugs but swapped them side-to-side and problem did not follow. Honestly the plugs have maybe 2 hrs total run time on them.
 

·
Registered
Joined
·
20 Posts
Discussion Starter #4 (Edited)
Think I might have found a possible culprit. I had replaced the slow jet on the carb in-question and when disassembling I noticed the the jet looked a bit deeper in the carb than the other. I measured and it is indeed about 1-2mm deeper. I pressed it in (with heat) until it gently stopped but maybe I should have made a tool to set the depth the same as the other carb. I'm going to purchase another jet, pull the one it it out it and press the new one to match the same depth. I wonder by being too deep it's blocking some of the air bleed into the jet and causing it to be too rich. Crossing fingers! Brad
 

·
Registered
Joined
·
7 Posts
Mine did the exact same thing. I found that the gas line from the petcock to the left carb was kinked so it was not getting gas (or enough to stay running). Fixed it and it has run perfect since. I was looking for more difficult problems like electrical and carb problems....then I saw the kink in the line. It could also be a clogged petcock. Just something else to look at.
 

·
Registered
Joined
·
20 Posts
Discussion Starter #6
Following up... I pulled the (too-deep) slow jet out from the left carb and pressed a brand new one in (#42) and used a tool to set the height to match the original one on the right carb. Reassembled, set both mixture screws to 1.75 turns and (drum roll) no change. Left side is still drowning in so much gas it won't fire and drips out the pipe. I took a chance and dropped the float on the left side by a good amount and tried again, with the right side plug wire off. It now tries to fire but won't run on that side. My next try was going to be to pull the secondary jet out and replace it with a plug and see if it's causing the issue. Also, I don't understand what the diaphragm of the side of the carb does and what part it plays in metering air to the idle circuit but could that be a problem? I've swapped all the parts side-to-side on the carbs and like I said, no change. Dying here. Brad
 

·
Registered
Joined
·
11 Posts
Are you sure this isn't an ignition problem? Do you have good spark on both sides? I don't see anything in your testing about this. There is a CDI box and the ignition stator, and the Hawks - especially the earlier ones - had problems with the ignition stator. They pretty well had it sorted out after 1979, but that doesn't mean it couldn't happen at random.
 
1 - 7 of 7 Posts
Top