SOHC.co.uk Forums > CB350/400
It’s all about the timing
Ken4004:
Thanks everyone for your input, I believe that I still have a slight issue with my carbs because the bike runs a little erratic below 1500 rpm which means when I am trying to set the timing the mark tends to bounce around a little so not as steady as it should be to set the timing.
I did think it might be my timing light because it’s not one of the clip on type it’s just a spring so you have to remove the HT plug and connect one end of the spring to the spark plug and the other end to the plug cap so it’s just resting between the two which is not ideal( I’ll attach a picture of the spring connector for reference)
I will therefore try and just set the points up statically and then re look at the carbs, I suspect that there is still a slight blockage in the idle circuit so carbs may will need to come off again and will try using guitar strings to ensure the galleries are totally clear.
This is only a slight issue and I believe I am very close to having the bike running spot on , once it idles at 1200 rpm without the occasional splutter I will assume I have cracked it
exvalvesetdabbler:
It's also worth verifying you are air tight in the induction side, inlets stubs onto the head, rubber bits both side of the carbs.
Sometimes a slight squirt of wd40 around a suspect joint will cause the engine note to change if there's a suction leak.
Also the screws for the vacuum ports, is there a soft washer under them?
Regards
Dave
Ken4004:
--- Quote from: exvalvesetdabbler on August 08, 2026, 08:59:10 PM ---It's also worth verifying you are air tight in the induction side, inlets stubs onto the head, rubber bits both side of the carbs.
Sometimes a slight squirt of wd40 around a suspect joint will cause the engine note to change if there's a suction leak.
Also the screws for the vacuum ports, is there a soft washer under them?
Regards
Dave
--- End quote ---
Thanks Dave that is a very good point, I am using the original joints on air box side and engine side.
They were originally very hard so I soaked them with a mixture of winter green and surgical spirts for a few days which softened them up enough to refit them and I thought they were OK but maybe I should have replaced them all, just trying to save a little cash as the project was getting a little expensive.
This in hindsight was probably a false economy but I was just trying to use a many original parts as possible.
I will there try the WD40 check to see if I indeed have an air leak .
exvalvesetdabbler:
It's the o rings between the inlet stubs and cylinder head that go rock hard.
Regards
Dave
Ken4004:
--- Quote from: exvalvesetdabbler on August 08, 2026, 08:59:10 PM ---It's also worth verifying you are air tight in the induction side, inlets stubs onto the head, rubber bits both side of the carbs.
Sometimes a slight squirt of wd40 around a suspect joint will cause the engine note to change if there's a suction leak.
Also the screws for the vacuum ports, is there a soft washer under them?
Regards
Dave
--- End quote ---
Actually Dave come to think of it I don’t remember seeing a soft washer under the screws so probably the first place to look, I didn’t think the system was as sensitive as that but it could be drawing in air in this area so a good call.
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