Help please - Stock UK model FB jet sizes

[TheDodger]

Hi can someone help please.

I pulled the carbs on my 1982 CB 750 FB DOHC 4 UK model.

The jet sizes in each are 102 mains and 68 pilots.

Are these correct stock size jets?

I don't think they are and the bike seems to be running lean with my Motad 4 into 1 exhaust.

Can someone give me some help as I need to put in an order for parts tomorrow.

Would really appreciate it.

Cheers.

[LukeM]

According to my Haynes manual, the carb model is VB43A, and VB43B for the Canada models.
If these are yours, the primary main jet is a 68, and the secondary main jet is a 105.

On some forums, they recommend moving up one size on both of these to help the engine run just a bit richer.  The factory jets were chosen with emissions controls in mind.

I hope this helps.
Luke M

[TheDodger]

Thanks a lot Luke.

So I probably just need to adjust the mixture of the carbs?

Cheers.

[Re-run]

Do you know what rpm range your bike is running lean? Run for a bit at 3000 rpm and then kill the engine and pull the plugs. If they are white, then your idle mix screw should take care of it. I know speed limits in the UK are fairly low but try to get the bike above 8000 rpm and then kill it and check the plugs there too. This will give you an idea where you are running rich.