SOHC.co.uk Forums > CB750

Running rich

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adrian58:
Nice day and took my K2 out for a 60 mile round trip, the first 'outing' since I bought her. All seemed pretty good other than it seems to be running too rich. Smoking a bit,(viewed by my mate behind me) white not blue. I got home  switched off straight away and let it cool. I whipped out No1 and No4 plugs and sure enough they were a bit wet with petrol and electrodes sooty. I'm sure the chokes are ok and the air filter is new. I suppose the answer is to change all the jets just wondered if there was anything I could try first.(Not much change from £100 for the D/S overhaul kit). Was thinking about lowering the throttle needle a notch or would a hotter plug help ? Any thoughts ?

K2-K6:
"wet with petrol" sounds like more than a bit rich, worth checking needle position and float heights first to see what you have before commiting any cash.

Also see what number mains they have fitted as well.

adrian58:
Was wondering about the float heights. I know if I leave the petrol tap on, one of the carbs will drip a bit from the overflow tube after a while. Still not dead sure how to set them. Would this cause a rich mixture ? Any tips would be welcome.

Waggles:
I would address float height first and check your float needle valves as it could easily be the carbs flooding. Any good manual will show you setting up the float level ( a picture is worth a thousand words! ) If you leave the petrol on with bike on the sidestand you can get fuel drip when you straighten bike up but generally they shouldn't leak. Although my F1 can occasionally, could be when its hot etc.

As for jets, remember that the main jet doesn't really have any affect until 3/4 throttle! before that its mainly idle jet and slide cutaway up to about 1/4 throttle then the rest is needle jet, so think how you ride before shelling out on jets etc

adrian58:
Is the throttle needle adjustable and if so what notch is the standard setting. I remember the previous owner told me he thought it was running a bit rich and that he had set the float heights with a vernier caliper. He did give the impression at least that he  knew what he was doing. Took it out again today and it does seem to be a bit lumpy at about 1/4 throttle. Tickover fine and if you wind it up it's ok. Could be a plug a bit soot-ed up.Thinking of trying a slightly hotter plug any suggestions what number ?

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