Topic: Air screw to reduce decel popping?

[PeWe]

I tested iridium plugs, NGK for CB750. They looked as they ran slightly colder than
NGK D8EA and Denso X24ES-U that work fine.

- Have you verified the needles yet?

If cheap aftermarket, it will not run well. It does not matter what you do. Wrong taper and thickness for the carbs.

[Don R]

 Forgive our enthusiasm, we get invested in these tuning threads and want to not only share what we have learned already but also learn more from them.

[Bigmant]

Forgive our enthusiasm, we get invested in these tuning threads and want to not only share what we have learned already but also learn more from them.

Totally understand!

Well here is another one. The plot thickens…

Pictures of cylinders 3 and 2 respectively with 3 appearing to be super lean.

[scottly]

Have you tried running the engine with the new plugs and jets yet? Also, since #3 is leaner than the other 3 cylinders, you should verify the fuel levels in the float bowls using the "clear tube" method. The level should be about 3mm below the top of the bowl where it meets the carb body.

[Bigmant]

I tested iridium plugs, NGK for CB750. They looked as they ran slightly colder than
NGK D8EA and Denso X24ES-U that work fine.

- Have you verified the needles yet?

If cheap aftermarket, it will not run well. It does not matter what you do. Wrong taper and thickness for the carbs.

How would you know if the needles are stock or not? And if they weren’t where would I get a set of genuine ones?

[RAFster122s]

The stylized K on the side of the carbs is stamped into the needles near the number identifying the part number.  The genuine needles are getting very hard to find new.
JetsRUs offers new carb parts made to proper dimensions but they aren't always Keihin parts, sometimes they are...just depends upon availability of the Keihin parts.

[PeWe]

I tested iridium plugs, NGK for CB750. They looked as they ran slightly colder than
NGK D8EA and Denso X24ES-U that work fine.

- Have you verified the needles yet?

If cheap aftermarket, it will not run well. It does not matter what you do. Wrong taper and thickness for the carbs.

How would you know if the needles are stock or not? And if they weren’t where would I get a set of genuine ones?

If you know if the carbs have got a cheap upgrade kit with all gaskets and brass. I bought a kit, saw that needles were different at first sight.

I tried to help a biker friend with jetting. Nothing worked, too rich. Finally he told me that he had replaced stock needles with crap needles. Lenght, thickness and taper not close.

Depending on carb type
064A  #271307 ( seen in my carbs and forum)
These needles middle notch

086A  #27201. (Found on this forum. I did not note the numbers in my set
These 4th from top as I have in similar setup.

It is well worth the hassle to check the needles and stamped numbers they have. All 4 must be same too.  You never know what a PO has done.

[scottly]

You never know what a PO has done.

The PO was the OP's father. Besides, the bike ran well with the needles it has now at one time.