SOHC.co.uk Forums > CB350/400

Starting to wonder about this bike.....

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Scottish Badger:
After resolving my previous cold start issues, today I finally rode my 400/4 for the first time seeing as it was a glorious sunny day on the Moray coast. 
Now, I'm not a small chap (around 18st 6) so I never expected any spectacular performance, but it actually surprised me. Not with the speed or acceleration (never went over 60 and I was using a lot of throttle to maintain that speed into a light breeze), but how solid and planted it feels. It corners very nicely indeed, it's surefooted, stable and not upset by road surface changes etc. The highest praise I can give it, it's like a smaller, lighter version of my triumph Thunderbird Sport 900.
There's a minor adjustment required to the clutch, I think I may have taken just a little too much free play out at the adjustment under the engine cover as it wants to slip slightly when changing gear quickly and winding the power on.  BUT........

Slowed to 20mph in a village, started running rough. Into 30 limit, open the throttle a touch and it clears itself. F8&%£"g carb flooding!!  It's had new float needles and seats, float heights set (making sure the floats themselves are level), a filter in the line from the tank, clean fuel, and it's sat running on the bike lift for over two hours with no issues whatsoever. First time out, it floods one of the carbs! Stay over 30mph, it's fine. Slow down below 30 and it does it every time! Maybe it's trying to tell me something.......

McCabe-Thiele (Ted):
That is very frustrating - is it always the same carb that is flooding?
I'm guessing at over 30 mph a combination of vibration & fuel use is keeping the flooding at bay.
If it was fine for two hours could it just be some dirt has worked it's way down into the needle valve seat?
Does it still have the narrow plastic pipe between the carbs or has it been replaced with more normal fuel pipe?

Scottish Badger:
Hi Ted.  Yeah, fuel usage at 30mph and above is enough to prevent the flooding. 
Frustration prevented me from actually checking which carb it was, but I can assure you there was no dirt in there anywhere and the filter is still clean as well.
I'm thinking I'll find what carb it was, drain it down and blow it back with the airline after taking the filter off and see what (if anything) comes out the fuel pipe.
The interconnecting pipes were all like new, more of a plastic than a rubber but still quite maleable - and clean.

K2-K6:
Certainly a real pain to chase yourself round and round it trying to get it reliable.

Experimental, but you could try adding two stroke oil to fuel, 100:1 so 10ml per litre to see if that'll help things to move effectively in the brass components.

Oddjob:
That's one of the reasons I asked Piki on the forum to make me some stickers for the overflow pipes, like the ones used on the HT leads, that's so if any start to leak I can look at the label and tell at a glance what carb is leaking fuel. Don't know why no one else seems to have done this before, seems a logical thing to do.

You may have a bent float pivot rod, the small brass ones the float hangs off. You can buy replacement rod off Amazon and make your own. https://www.amazon.co.uk/gp/product/B00JR5CG88/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 I polish them as well before fitting, every little helps.

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