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Hi all! First post for me, although I have used this forum for a ton of information. I purchased a 1972 CB350 K4 from Ohio. It was not running when I got it, but after some efforts, I got it running reasonably well. Here is what I have done:

Replaced:
Battery
Plugs (B7ES)
Coils & wires (Coils are Yamaha XS coils)
Points & Condensor
Pod air cleaners
Fuel Petcock
Carb rebuild including all jets, floats,
In-line fuel filters

The bike was running quite well with a new battery & plugs, and adjusting the timing, point gap, valve clearance, and cam tension. Occasionally the right side would die. After troubleshooting, I did not have spart on the right side, so I replaced the coils, condensor, points, and plug wires. After this the spark seems strong.

The bike would occasionally lose power, and it seemed to be fouling out the plug, so I checked the right side, and it was definatley wet with fuel, the left side looked very good. After taking apart the carbs, cleaning, and verifying the float height (26mm), I decided to change from B8ES to B7ES plugs to reduce the fouling issue.

However, the bike now misses at high RPM's (over 6k). It seems to do this consistently.

I checked the battery and it is 12.8v across the terminals while running. With the light on low it drops to 12.7, on high it drops to 12.6 at idle. When I rev the bike it quickly goes to 13.0 v, so I believe the charging system is working.

The bike was also stalling after running for a while, but I believe that is due to the gas cap not letting the tank vent properly. With the cap open, the problem goes away.

I do occasionally get a backfire at idle until it warms up.

Any ideas on why it would miss at high RPM's? :cry:
 

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72 CB350
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I'm assuming you figured this out by now but this seems relevant:
 

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Apparently this guy in the video is smarter than the OEM Honda Engineers. - I'm going to vote NO on that one.
This is a solution to a NON-EXISISTANT problem.

The fact is (2) points he has wrong.
1 - It is a CLOSED System his demonstration allows air to reverse flow to the Petcock.
When installed both hose are a closed system with NO ACCESS to an OUTSIDE AIR Source as they are connected to the Carbs via the Float Bowls.

2 - With Motion the floats move a little and the level in the float bowls moves a little.
Each time a Float drops it allows the Fuel to flow. This doesn't always happen at the same time for both Carbs.
First one will refill then shut off then the other will refill rinse and repeat.
This works just like him pinching off one tube then the other.

I can shut off my petcock and run easily for 1/2 Mile at highway speeds before any fuel starvation begins to occur.

NOW Back to the Original Posters Issue:
He already has answered his own questions/problem.
He knows he has an issue with the gas cap vent. - FIX THAT 1st.
Also he Rebuilt his Carb - INCLUDING ALL JETS. - The OEM Brass parts Jets etc. should be reused unless VISIBLY ABUSED.
It has been proven time and again the Aftermarket Jets are notorious for being incorrectly sized.
 
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