Topic: Fuel efficiency on a CB750K1

[bryanj]

Hi Raul, never found two bikes yet that did the same MPG, dont forget to take into account when comparing figures that a US gallon is smaller than a UK gallon as the yanks are more logical!! (UK 16 ounces = 1 pound and 20 ounces = 1 pint US 16 ounces for both) Cant really remember what they were doing when i was a lad  but at a guess 35-40 is about right. You really need to do a plug chop but remember this The colour of the porcelain centre tells you if the plug temp is right the mixture you take from the flat steel rim with the earth electrode on it which should be a light grey idealy. It is probable that the carb settings will need to be different from stock as the "bang" quality of the fuel we get now is not the same as the early 70's They havent just taken the lead out which is why it goes stale so damn quick now. Hope that helps Bryan

[Raul CB750K1]

Thanks Bryan. I made the conversion as 1 US gallon=3.78 liters. My measurement was done in liters (assuming the pump was accurate, as 10 years ago there was a big scandal where some pumps had a 10% tolerance!!).


I think I'm going to change plugs first, and probably will delay the carb settings until october (taking jet needle one notch up, that means that the needle will be deeper inside the jet, thus reducing the amount of fuel sprayed). Now it's riding season and I don't want to spend riding time tinkering: I have plenty of time to do it later. At the end, if it runs rich will only afect my wallet (that I agree is cheaper than therapy), and erring on the rich side is much safer for the bike than erring on the lean side.


Thanks again everybody!!!

Raul

[CB750F2]

My 78 F2 has about 1000K since rebuild and I appear to be getting about 5l/100k. My rides have been fairly short but I try to run around 4200 RPM when traffic and road conditions permit. The colour of plugs 2&3 are perfect while plugs 1&4 are slightly sooty. I have tried changing 1-4 coil and new plugs but no change. I am now trying to lean out the idle mixture air screws for 1-4 carbs. Compression and timing are OK. Float levels are OK but maybe I need to drop them slightly on 1-4 carbs. I am using NGK D7EA plugs which are slightly hotter than standard. Pat from Nth Qld

[StephenB]

Stock CB750K1 (18/48 sprockets), baffled HM341 pipes, stock air filter, using the whole rpm band resulting in plugs with a nice brown tan gets me approx 160miles to the tank before reserve ... roughly 45mpg (US)