CB77 Carb Settings

[Merz64cb77]

I have what I think is a simple question about the carb settings on my CB77.

I have stock PW26 carbs with #135 main and #42 slow but am operating with 4th over oem art pistons.

Would this require a change in size to the jets or clip height on the needle to maintain the correct fuel/air ratio.

Thanks

[DJM]

Not in my experience.

The carb is a pretty crude device which mixes fuel and air at hopefully the correct ratio for the engine to burn,

If you increase the bore size, theoretically the engine will draw more air through the carb which should still mix in the fuel at the correct ratio.

Percentage wise you haven't increased the engine size much anyway, if it's still running OK I wouldn't worry about it.

[G-Man]

As DJM says, carbs are all about air / fuel ratio. The carb doesn't 'know' whether it is handling a 500cc cyclinder running at 5000 rpm or a 250cc cylinder running at 10,000 rpm.

My 1961 CB72 had a 350 kit and was still running stock 23mm carbs with stock jets. The colour of the combustion chambers showed the engine had been running nicely.

G

I have what I think is a simple question about the carb settings on my CB77.

I have stock P26 carbs with #135 main and #42 slow but am operating with 4th over oem art pistons.

Would this require a change in size to the jets or clip height on the needle to maintain the correct fuel/air ratio.

Thanks

[Merz64cb77]

Thanks for the information gents, I really appreciate it. I’ll keep the carbs the way they are.

[G-Man]

Although this guide is aimed at a differnt carburetor, they work on the same principle. If you need to alter the settings then it helps you work out which direction to go.

http://amalcarb.co.uk/downloadfiles/ama ... _guide.pdf

Bill Silver made a comment recently that he uses #140 main jets to compensate for the ethanol in US fuel. I'm not sure what you use in Canada but it may be useful to know.

G

Thanks for the information gents, I really appreciate it. I’ll keep the carbs the way they are.

[Merz64cb77]

Thanks for sharing G-man. I believe that most petro stations in Canada sell fuel that contains up to 10% ethanol at least for 87 and 89 octanes. I’ve also heard that some stations sell 91 and 94 octanes without ethanol. I only use 94 octane.