Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: neat street on August 31, 2024, 11:33:20 AM
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good morning all
I have read somewhere on this forum a way of setting up the carbs beffore putting them back on the engine?? I seem to recall that you can set the heights of the slides by sliding a small drill bit under each one to set them which i beieve was a 3mm bit? can onyone please confirm, or has a different solution please?
thank you
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No that’s the way to do it, works a treat, while youve got them off, might be handy to check if your float height skills and run some fuel through them to check for leaks, see picture.
Beats taking them on and off!(https://uploads.tapatalk-cdn.com/20240831/ce972b33c8550e5661c01b4e52a27c0e.jpg)
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good morning all
I have read somewhere on this forum a way of setting up the carbs beffore putting them back on the engine?? I seem to recall that you can set the heights of the slides by sliding a small drill bit under each one to set them which i beieve was a 3mm bit? can onyone please confirm, or has a different solution please?
thank you
IMHO 3 mm is way too much for a bench synch, on my 400 I used an odd sized drill shaft iirc it was 5/64 so a tad under 2 mm.
On my 500 I did it slightly differently as instead of a measurable gap I went for the point where the slider just started to lift/move off the bottom of the carb body. I found I ran out of thread on the main stop scew on the carb array bracket so had to build up the lug where the stop screw meets the bracket.
Certainly worth checking the carb bowls for flooding after you have checked/adjusted the float heights using a small header tank (as per Roo's photo) Much easier than having to take the carbs off again.
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The diameter of drill, or similar, should have no impact other than being in range of the "master" idle screw threads to allow tickover adjustment competently after install.
If for example you just open the throttle mechanism and place a spacer underneath that screw to stop it dropping the slides, then any resulting gap under the slides can be set to parity across all four, doesn't really matter if it's 3, 5 or 10 mm there, as long as you set them the same, then take out the spacer to drop the throttle mechanism back to correct position.
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The advantage I believe of a narrower gap when bench setting is you can easily obtain a lower idle speed.
If you set it at 3 mm it might idle too fast. I found this helpfull when dismantling carbs. He uses 1/8" drill shank I went for smaller.
https://www.vintagebikebuilder.com/cb350-400f-carb-rebuild-demonstration.html
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Thank you all for your help and comments, I will certainly check for leaks after the bench test.
appreciate all your comments :-)
Thanks
John
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The diameter of drill, or similar, should have no impact other than being in range of the "master" idle screw threads to allow tickover adjustment competently after install.
If for example you just open the throttle mechanism and place a spacer underneath that screw to stop it dropping the slides, then any resulting gap under the slides can be set to parity across all four, doesn't really matter if it's 3, 5 or 10 mm there, as long as you set them the same, then take out the spacer to drop the throttle mechanism back to correct position.
That's a neat idea Nigel - what size spacer would be ideal?
I'm thinking of trying out that idea on my spare set of 400 carbs that need bench such as I have finished overhauling them. Would 3mm be about right? Does this method impact on the throttle quadrant fully opening the carbs?
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jst as expected, fuel leaking and need to order a full set rebuild kit x 4 (complete with float needle and seat) any ideas, or does anyone on the forum sell any? (its the 1976 750F1)
thank you
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Dont buy kits the sizing is not correct just strip and clean the brass in an ultrasonic, you could ask Nurse Julie if she does the O rings for those
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I fitted keyster seats and float valves on my CB350 four and I’m now getting intermittent fuel leaks. Will be replacing them with the correct (but costly) parts
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When rebuilding my 550 carbs I found this video very useful:
https://m.youtube.com/watch?v=JFTOfYl5BSc&list=PLIVVFRFycxy0mOuDKDdsZuICXz_CXDm59&index=3&pp=gAQBiAQB
Also agree that Nurse Julie is where to go for any necessary carb parts!
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thank you all again for your help, appreciate you taking the time to reply.