SOHC.co.uk Forums > CB350/400

Carbs overflow

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DaveN:
Hi All,

I've only put 450 miles on the 400 since the rebuild but it is regularly overflowing the carbs and depositing lots of petrol on the ground if it's been standing for longer than a few days.

First time the overflow stopped after a long run and all was well.
Second time it did not and I had to take off the carbs and give the float valves and bowls a good clean out (some reddish deposits in all of them).
Not ridden it for 10 days and again, most of the petrol is ending up on the floor even after a 60 mile run. I've tried knocking the float bowls with a screwdriver handle but the overflow persists.

Looks like I have to have the carbs off again and was just wondering if this is a known issue with the 400/4 or have I a rogue set of carbs? They all benefitted from a DS carb repair kit during the rebuild. The bike runs well with no noticeable flat spots so I presume they are set up OK and the inside of the tank looks fairly clean.

Any suggestions or advice welcome.

Johnwebley:
It sounds like light corrosion inside the tank coming off as it's being used.

Check the tap filter.

Maybe put some Redex carb/injection cleaner in and see how it goes

Sent from my SM-A750FN using Tapatalk

Laverda Dave:
I feel your pain as a lot of 400/4 owners do!
I think it is widely accepted the brasswear of the rebuild kits is not as good as the originals. If you can clean the old brass in an ultrasonic cleaner and they are spotless try to re-use them with new gaskets.
A lot of the overflowing issues are caused by the fuel inlet needle not seating correctly (especially with the new ones).
One tip is to remove the needle valve itself and to use a cotton bud in a drill and polish the brass seat of the valve with some Solvol or similar on the cotton bud. Strip the cotton off the other end as you need to hold it in the drill. Once polished give the seat a really good clean to remove any polishing residue.
Also, make sure the float heights are 100% spot on, make up a gauge to set the height, using a ruler is very hit and miss especially for the middle two carbs if they are mounted on the rail.
You'll find being a 400/4 owner you will soon become an expert at removing the carbs!
Good luck 🤞.

taysidedragon:
As above, plus always turn the fuel tap off when parked.
It's easy to forget if used to modern bikes with no tap.

Nurse Julie:
As above but turn fuel off ¼ mile from home so the float bowls are almost empty when you get home which avoids the floats pushing on the float valve springs when the bike isn't in use.

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