Topic: Carburetor venturi size

[MisterKnife]

Currently, I am finetuning my set of VM34 2-4 carburetors for my CB550 motorcycle. After adding the ufo mod, they are performing exceptionally well. The air/fuel ratio (A/F) is stable at 13-13.5 during idle and remains consistent at 11-12.5 all the way to wide-open throttle (WOT) throughout the power band. This setup provides excellent power both in the upper and lower bands.

However, I have noticed an issue: when the bike is cold, the idle isn't as smooth, and it takes some time to warm (5 minute ride) up before returning to its optimal performance. I am wondering if switching to a set of VM32 carburetors would improve this problem.

I might in the future jump on a set of CR 26's again but I just want to understand the workings of it all.

[Deltarider]

We need to know a bit more. What air intake tract do you have, including the filtering and - less important - what exhaust system do you run?

However, I have noticed an issue: when the bike is cold, the idle isn't as smooth, and it takes some time to warm (5 minute ride) up before returning to its optimal performance.

Please note that every CB500/550 owner will recognise this as normal behaviour for these models. They are all coldblooded and need a raised idle - either by your hand at the throttle grip* or a temporarily turned idle adjust knob to a higher rpm  - for the first few minutes.
* This is even mentioned in the Owner's Manual.

[MisterKnife]

It's the intake tract from Murray: https://murrayscarbs.com/wp-content/uploads/2019/10/IMG_5005-510x680.jpg
Exhaust is delvinic header with cone eng short muffler but I added a db killer that is restrictive.

[MisterKnife]

We need to know a bit more. What air intake tract do you have, including the filtering and - less important - what exhaust system do you run?

However, I have noticed an issue: when the bike is cold, the idle isn't as smooth, and it takes some time to warm (5 minute ride) up before returning to its optimal performance.

Please note that every CB500/550 owner will recognise this as normal behaviour for these models. They are all coldblooded and need a raised idle - either by your hand at the throttle grip* or a temporarily turned idle adjust knob to a higher rpm  - for the first few minutes.
* This is even mentioned in the Owner's Manual.

Yeah, I get that there should be a warmup period I think on mine with the larger venturi causing bad fuel atomization. So my chain of thought was that if I reduce the venturi the atomization would be better. But thinking about this the pilot circuit bypasses the venturi for the most part... So it's more the cause of the intake manifolds being long I guess.
Diving into that, would a very short manifold with a straight path to the inlet have a reduced warmup time?

[TwoTired]

What spark plugs are you using?   I found that plugs for a CB750 are awful during warm up on a Cb550.  CB550 prefers a hotter spark plug.