SOHC.co.uk Forums > CB350/400
My 1975 CB400F restoration project
Cb750r:
--- Quote from: ozzybud on March 05, 2024, 03:10:43 PM ---
--- Quote from: Cb750r on March 05, 2024, 03:04:26 PM ---I chased my tail jetting my 750 for quite some time, what really frustrated me is a lot of carb tuning states to get the main jet sorted first and work your way down…
In my scenario to get it to run right wide open was too lean at idle and to get it to idle the main was super rich, I played with countless needle positions and float heights and in the end a bigger idle jet sorted things out.
I will second what others have said about non genuine brass, even in sport bikes I’ve jetted I try and avoid non genuine jets/needles.
Just another thought, where are you elevation wise? We have from sea level to fairly high base elevations in the pacific west coast to deal with, and small bikes have less hp to deal with jetting that’s off for your ‘base’ elevation. My snowmobile actually had a dial to lean out jetting as I climbed to keep it running optimally as I climbed. I’ve also had dirt bikes with ‘mild jetting’ changes from stock that are widely used elsewhere but would foul plugs at my elevation. Maybe your bike was ‘ok’ or slightly rich at sea level and you’re too high for it to run well now?
--- End quote ---
I am at or near sea level
Seattle Washington
My plan is to get everything back to rather stock settings and jet. #s then go from there. I have 4 OEM #75 jets on the way
--- End quote ---
Well then it’s not elevation related unless you went straight up snoqualmie pass on your test loop! It’s crazy how sensitive some bikes can be to changes. That dirt bike I got to run great, but with a spark arrestor would still foul plugs so I needed to be leaner than stock for the elevation and modifications I had to ride in the woods here.
eem46:
Hi, great looking bike! Which clutch basket rubbers did you use? Which dealer/brand? Kind regards, Emiel
ozzybud:
i ordered these from the UK
https://www.ebay.com/itm/156080700060?itmmeta=01HSHKFBZTS2FDQZR7835J6AZ1&hash=item2457227a9c:g:2MgAAOSwNetloepT&itmprp=enc%3AAQAJAAAA8JuGvduuE6KzzeGdWVTIKHG8yM1kafSVMCQtNMKEGWBgih9OeKWIuYacbVWT0D4wjNvC7ntLpzpXneD%2BIiiIpd69UTE4MlOKGuVr9D2Q%2F0pc2S7qr5nfJeGBAPc%2F7EOeR5Ykxsw0Yd%2Bt3s8R9BLeLo%2B7b6XiV0gM26rpeGRTcTiEYzdYLOIs%2BkpJ2S0I8n2APopOvN9oqOER57G66FHYX04uKEKlygdL5NJCuebGPZWTitWfMFy45NYRs2yiFuq2KqeXxSNtyKQYT8TH05PFDHeeW0WaS5gSilz4an9bvIO6vxptT1XIBn7gMz9zEccrRA%3D%3D%7Ctkp%3ABk9SR4jAvbPMYw
Mine were type "B". it is my understanding that Most 408 cc bikes use Type "B" and the 398cc motors use Type "A".
ozzybud:
I finally received the rest of the correct Keihin brass from CMS yesterday. I got the carbs assembled and setup on the bench as close as i could get them synchronized.
As I suspected the previous owner put in some larger Jets and messed with the Needle position. There were #90 main Jets #44 slow and the needle clip was at the bottom groove. pulling the needle up to full rich. I replaced with #75 main #38 slow and clip in the middle position .
Took it out yesterday between showers. Wow what an amazing little bike. ran like a Swiss watch.
Cb750r:
--- Quote from: ozzybud on March 22, 2024, 04:52:37 PM ---I finally received the rest of the correct Keihin brass from CMS yesterday. I got the carbs assembled and setup on the bench as close as i could get them synchronized.
As I suspected the previous owner put in some larger Jets and messed with the Needle position. There were #90 main Jets #44 slow and the needle clip was at the bottom groove. pulling the needle up to full rich. I replaced with #75 main #38 slow and clip in the middle position .
Took it out yesterday between showers. Wow what an amazing little bike. ran like a Swiss watch.
--- End quote ---
So glad to hear you sorted out the jetting! Congrats!
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