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cb750 carbs

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Waggles:
Point is, if, with screws fully in, plug colour and mixture is OK and she runs OK at least you know the problem is with the idle circuit.

Seem to recall from the book there are jet differences in emulsion tubes, can't remember why or what difference this makes, will try and remember to check the book this evening.

Can you take her for a brisk run then pull a plug in a lay by or something to see if the needle etc is OK? might eliminate some bits

Bitsa (Ralph Wright - RIP):
Yo Waggles,
Appreciate this as for a run wont get around to that until Thursday because of commitments will do what you say and pull outside plugs down the road.I have managed to find some 42 slow jets might try that after results on Thursday.
Cheers
Bitsa

Waggles:
OK this is interesting. I always believed there are 2 types of adjuster screw on carbs, one type controls the supply of fuel to the pilot jet, the other type controls the air supply. I know the 750 carbs use air supply screw. I would have therefore thought that screwing in the screw restricts the amount of air and richens the mixture, much the same as you if I read your posts correctly. Just read Hondaman's book, he states screwing it in WEAKENS the mixture. Apparently, increasing the amount of air ( by screwing the screw out ) pulls more fuel out of the jet and forcing it into the venturi so richening the mixture.

I have only ever 'twiddled' until it runs best! The advice, therefore, seems to be turn your screws OUT by another half a turn as the standard setting is around 1 turn out. Give it a try, thats where mine are set.

I was right in that there are differences with ikkle holes, not in the emulsion tube but in the actual air screw, some have solid tips, others have small holes in the tips, you could also try changing them. The book has nothing to say regarding which type is best or what the effect is.

Hope this helps. I really recommend the book, expensive but worth it!

Seamus:
That makes sense Waggles. If opening the screws tends to drop the idle, then the only option is to adjust on the throttle stop till it works.

I am also guessing that the carbs have been balanced and therefor not being led or hindered by one or two in the group.

Keep us posted

BigAl (Alan):
Hi Bitsa,

I have assumed you have re-built the carbs with 'Keyster kits' ? the needle & needle jet in these kits are for the  early CB's (size 120s)  for your model K4 they are 105.
I had a similar problem, but once I fitted the 105's from DS it sloved the problem.
Have you set the needle clip plates on the middle position?

Alan

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