Carb flat spot

[AussieLoki]

Hello, hope you are all well. My 2001 cb250 has a slight flat spot coming off idle which I know is from the carb tuning. Any suggestions on how to fix this? Outside of that it runs well.

As well if left to idle it will foul up the plugs quick, but from my time working with old timers this is standard to me. If that shouldn't be happening please let me know.

[Bob H]

Was the stock air filter removed?
Running pods?
Engines are designed to run at a known air intake vacuum, especially important for our Constant Velocity carbs.
I would put the stock parts back in, or get them from Ebay if you didn't get them with the bike.

[mollusc]

I think the CB250 came with only a single carb, so fitting a pod filter is less of an issue than with a multi-carb setup.  With multiple carbs, the separate individual pods simply cannot deliver a balanced and tuned airstream across all carbs at once.
With a single carb, you're dealing more with the fact that you've lost almost all backpressure so your vacuum slide is fluttering too much.
The usual way to deal with it is to stick a larger primary jet in the carb.  Your fuel economy goes way down and it doesn't really fix the problem -- it just disguises it -- but you then get to stubbornly claim that it runs fine anyway.

[AussieLoki]

it just disguises it -- but you then get to stubbornly claim that it runs fine anyway.

Ahaha, yeah it is a single carb. Running a pod as Bob predicted, not the most keen on tracking down and chucking the stock air box back on. Back pressure would make sense as the baffles are pretty much completely blown out and if I can avoid just dumping more fuel to fix the issue I'll do that.

I'll tune the vacuum advance and if no go seems I'll be taking the pipes off soon to put some new baffling in it. It's only noticeable just going off idle which isn't the end of the world as I'm definitely not racing anyone off the lights in this machine 
Thank you all for your help!

[Bob H]

Running a pod... not the most keen on tracking down and chucking the stock air box back on.

This video mentions the vital "Pod-ectamy" at around 3:15 minutes in.

I'll tune the vacuum advance...

Huh? You are talking about ignition timing? That will just give you a new problem.
I don't know that your bike even HAS a vacuum advance. I know mine doesn't.

[AussieLoki]

I'll watch that video, also yes don't know why I said vacuum advance. Last time I checked bikes didn't come with distributors . I think a mix of a nasty flu and inhaling brake clean from working on a diff in my garage is making me go delirious...

[AussieLoki]

Just watched the video, must admit it did give me a chuckle. I'm afraid I got to my bike to late, but I know where you are coming from. I own a old jap car that is famous in tuner culture so many of them also turn in teenager wet dream hackjobs. I've been able to protect mine and keep it incredibly factory with only changing out the hideous stock 17 inch wheels for some simple but nice 18 inch 5 spokes.

For the issue of running lean, I know from a racing buddy that velocity stacks help, but I'm thinking of doing a restricting mesh or I'll do some research on what the intended pressure was for the 250. Open up my CAD software and model the carb intake, then design some sleeves to put inside which will restrict air flow, do some cfd analysis and see what sleeve diameter gets me closest and boom should be fixed.

Is it a over complicated process? Yes
Is it the right way to do it? Probably not
Should it work? In theory