SOHC.co.uk Forums > CB750

Running rich

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K2-K6:
The plugs won't change the mixture even if you change the heat range.

Info for plugs if using NGK is usually 8 as standard....if you go for example to 9, then this switch is for the engine running hotter as the plug tranfers more heat away from the tip so that it won't start to overheat the electrode. This may be applicable if you were to use the bike for extended high speed work.
If you were to go for example to a 7, then this would be more applicable if you were running the bike in lower ambient temperatures so the electrode would stay hotter and give less risk of fouling ang giving poor ignition....it's unlikely for normal road use in this country to need anything other than 8 grade NGK.

I'd take a guess, as you say there is some leaking, that you first need to look at the fuel valves controlled by the floats.....this has a big influence over the observations you've made so it would be wise to verify that they are ok before going any further.

Waggles:
+1 on what K2 said. If a carb is flooding it will affect all settings so you need to address that first.

Yes, the needle position is adjustable by setting which groove the holding clip is in, higher groove = weaker mixture and vice versa

adrian58:
Just spent 2 hrs getting nowhere in the garage. Wanted to drop the throttle needle a notch but there was no way the two little screws inside the the throttle slide were going to budge to get to the needle. Any ideas how to shift them. There appears no signs of the carbs flooding which kind of steers me away from the float needles being the problem. I'm thinking that it may be a better option to buy the carb kit and fit it all rather than just the float needles and seats. Still will need to get at those throttle needles though.

Bitsa (Ralph Wright - RIP):
Hi Adrian,
When back in the old days I was a mechanic owners used to say can we watch you fix our bikes while they wait.As this was not allowed because when you see some gorilla banging the crap out of your desire it did not go down well.To get those 2 stupid little screws out first soak them with wd40 then protecting your slides from getting damaged hit the top of the screws with a blunt T bar if you like swiftly and they will come undone bit like a impact driver.I have done it all my life that way and have got out all the bast++d cross head screws I have encountered.Like I said protect your slide before you do this.I would really double check your float heights first and clear every orifice you can find.
Hope you have success.
Bitsa

adrian58:
Thanks Bitsa, going to try that thing with the clear plastic tube on the drain plugs to see if I can see if  the level is too high. I recon (if my research is right) level should be about 2mm to 4mm below float bowl joint. Don't mind spending the money on parts but being a mean bugger don't want to waste money either.

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