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CB350 1971 Restoration Project
BenPowell:
I’m fairly confident the diaphragms are fine, but they will be coming apart so won’t hurt to have another thorough check of them to be sure.
I do think it is a blockage somewhere, as I mentioned they were in a right state when I got them so in all honesty I’m surprised they work at all ;D
Just need to keep chipping away to find the root cause, like I mentioned I’ve checked and adjusted points and valves, going to run the bike tomorrow night to see if that’s improved anything, while it’s running I’ll check for vacuum leaks.
If the problem still persists, the carbs will be coming off for another thorough clean. Really don’t think it’s anything too major though, the bike will idle nicely at 1200rpm rev freely (no engine load) just the odd pop from one the right cylinder.
AshimotoK0:
I was only thinking earlier this evening if anyone has ever fitted 450 style CV carbs to a 350K and lo and behold this pops up on eBay ... a real mish-mash of an example.
https://www.ebay.co.uk/itm/386144812818
Ben ... did you try checking for inlet leaks with easy start sprayed onto the inlet stubs ... should have let me soften them with my magic fluid ;D
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philward:
Had a day on the 350. Rechecked all the settings - points bob on but timing (using the strobe) altered slightly, fiddled with carb setting and much improved but still intermittently hanging before settling to tickover. When I was building the engine on the bench and when fitting the carb manifolds, I thought the design of using JIS cross head screws and a gasket didn't seem a good design. The last thing I checked today was for air leaks on the carb manifold to head (using the carb cleaner method) and there was a clear movement in the revs when carb cleaner squirted at the joint.
Just spent the night stripping and re-assembled using a slight skim of silicon sealant and hexagon bolts.
I'll report back tomorrow
As an aside, its taken me back 50 odd years taking the tank off (when I had a 250k) and that bloody awful petrol balance pipe that goes from one side of the tank to the other under the frame - you have to juggle taking the tank off while trying to stop petrol coming out of both sides - its a bludy pain! I have put 2 tiny inline taps on the pipe (and disconnect the pipe in the middle between the taps) but there is so little space, its more trouble than the standard pipe.
Coincidence that Ash posted the same thing at the same time!
BenPowell:
--- Quote from: AshimotoK0 on September 26, 2023, 09:38:42 PM ---I was only thinking earlier this evening if anyone has ever fitted 450 style CV carbs to a 350K and lo and behold this pops up on eBay ... a real mish-mash of an example.
https://www.ebay.co.uk/itm/386144812818
Ben ... did you try checking for inlet leaks with easy start sprayed onto the inlet stubs ... should have let me soften them with my magic fluid ;D
(Attachment Link)
--- End quote ---
Will check for leaks tomorrow night, I hope it’s a leak, at least it’ll be fairly simple to do something with ;D
BenPowell:
--- Quote from: philward on September 26, 2023, 10:04:20 PM ---Had a day on the 350. Rechecked all the settings - points bob on but timing (using the strobe) altered slightly, fiddled with carb setting and much improved but still intermittently hanging before settling to tickover. When I was building the engine on the bench and when fitting the carb manifolds, I thought the design of using JIS cross head screws and a gasket didn't seem a good design. The last thing I checked today was for air leaks on the carb manifold to head (using the carb cleaner method) and there was a clear movement in the revs when carb cleaner squirted at the joint.
Just spent the night stripping and re-assembled using a slight skim of silicon sealant and hexagon bolts.
I'll report back tomorrow
As an aside, its taken me back 50 odd years taking the tank off (when I had a 250k) and that bloody awful petrol balance pipe that goes from one side of the tank to the other under the frame - you have to juggle taking the tank off while trying to stop petrol coming out of both sides - its a bludy pain! I have put 2 tiny inline taps on the pipe (and disconnect the pipe in the middle between the taps) but there is so little space, its more trouble than the standard pipe.
Coincidence that Ash posted the same thing at the same time!
--- End quote ---
Sounds like you’re getting to the bottom of the issue, just out of curiosity when trying to set up did you find the mixture screws made no change to the running of the engine? While mine was idling I was messing with the screws on both carbs, but didn’t seem to do much. So I just left them about 1 turn out.
To me that sounds like something in the idle circuit is blocked, additionally the idle speed screws are quite far in to maintain a steady 1200rpm idle.
The tank balance tube is a pain, I left mine a little longer just so i can prop up the bottom of the tank for access without removing it fully, ideally 2 clamps and a straight connector in the middle of the balance tube would work nicely.
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