SOHC.co.uk Forums > CB350/400
I think the slides are in the wrong bodies
Cappodimonte:
--- Quote from: Eldrick on September 21, 2022, 03:17:27 PM ---Ran the bike today and it all seems great, put the vacuum gauge on the carbs when I got home and I get this;
(Attachment Link)
#3 does show 10-15cmHg when I blip the throttle but otherwise, adjusting that slide just increases or decreases all the others by variable amounts.
Plugs are new, air flow upto the carbs is sealed so it could be a leak on the other side (the boots?). I did swap the vacuum tubes over to make sure that #3 tube and the carb tune wasn’t faulty. If it wasn’t for the vacuum gauge I just wouldn’t have known anything was wrong as the running response and idle seemed good. Well to my untrained mechanical brain anyway.
--- End quote ---
Is the bike running on all four cylinders or does it feel lumpy, as a 3 cylinder runner will sound ‘off’ and certainly will lack power. Do a quick check of the vacuum gauge by a light continual suck to see the mercury rises on each tube,
If all tubes rise and maintain their reading then you have discounted the gauge as a problem, if three falls as you maintain a suck then their is a fault in the gauge probably the rubber or it’s fixtures at either end.
Once you have ascertained if the gauge is faulty or not then proceed with the next step with engine running use a spray water bottle with soapy water and lightly spray the inlet tracts from carb to head, if there is an inlet leak the soapy water will stop it up for a short time and the gauge will rise, then fall which will prove or disprove this particular part as the problem, it has an ‘O’ ring seal which can flatten and leak, if the inlet rubber tract has a split then the soapy water will seal it but get dried out by the vacuum in a short time.
It’s all time consuming as is checking the inlet valve which in my opinion have closed up to almost zero mm to cause a vacuum drop.
Enjoy finding the fault
Sesman:
Try swapping the vacuum tunes to make sure it’s not the instrument.If the bike is running as well as you mentioned earlier in the thread I doubt the issue can be catastrophic…
Oddjob:
One persons running well isn't always an accurate description unless you know exactly how it should feel.
Ted ran his 400 on 2 cylinders and even though he said it seemed to lack power he didn't spot it was only running on 2. Sorry Ted for bringing that back up but it's a good example.
McCabe-Thiele (Ted):
Not only that but it did some trips to Ashbourne on 2 cylinders! 😁
Eldrick:
--- Quote from: Oddjob on September 21, 2022, 07:07:50 PM ---One persons running well isn't always an accurate description unless you know exactly how it should feel.
Ted ran his 400 on 2 cylinders and even though he said it seemed to lack power he didn't spot it was only running on 2. Sorry Ted for bringing that back up but it's a good example.
--- End quote ---
True, I thought it was running great and sounding great, the vacuum gauge told me otherwise. I would have happily run the bike forever in ignorance otherwise. Now, I'm on a mission to fix it and expand my knowledge. ;D
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